FIELD ARTILLERY
MATERIEL

Notes on the Development,
Use and Care of Modern Field Artillery
Equipment, Including the

3” Field Gun, American, French and
British 75s, the 4.7” Gun, 155-mm
Howitzer, GPF, Fire Control Instruments,
Signal Equipment and small
arms used by the Field Artillery—automatic
pistol, automatic rifle and
the Browning machine gun.

Compiled by

JAMES P. KELLY
1ST LIEUT. FIELD ARTILLERY
U. S. ARMY

COPYRIGHT
BY
THE UNIVERSITY CO-OPERATIVE STORE
UNIVERSITY OF MISSOURI
COLUMBIA, MO.

1920

DEDICATION

To those efficient officers and inspiring gentlemen who interested the “youngsters” of the Yale batteries in the service of their country, and, in a time of peace, prepared them for the duties which they later performed in a time of war, this book is gratefully and respectfully dedicated.

ARTILLERY OF THE FUTURE.

SELF-PROPELLING CATERPILLAR MARK VII 75-MM. GUN. MODEL 1916.

SELF-PROPELLING CATERPILLAR MARK II 155-MM. FILLOUX GUN.

INTRODUCTION.

The compiler of this volume believes that the Field Artillery student should possess a broad, general knowledge of the history and development of ordnance, with some idea of the elements of gun construction; that he should be acquainted with the organization, ideals and practicalities of modern field artillery armament; that he should know the ammunition and the guns in our Field Artillery service with their care and maintenance.

It is also believed that in the R. O. T. C. units of Field Artillery the student should make the complete 3” equipment the basis of his knowledge of materiel. He should become thoroughly and familiarly acquainted with this weapon, and, to a lesser extent, with the other light pieces which are in present use. The reason for this being that our experience in the World War has shown that a thorough knowledge of one class of materiel permits a ready adaptation to any other type. He should also know the manner of functioning of the 4.7” and 155-mm rifles, with a somewhat more intensive knowledge of the 155-mm howitzer—and with a sound knowledge of the capabilities and limitations of all.

To complete his instruction in materiel he should know the use and care of Fire Control equipment, Signal equipment, and the small arms used in the field artillery, pistol, automatic rifle and machine gun.

The lack of a single volume covering the above has been the cause of the compilation of this book. The compiler hopes the R. O. T. C. student will find in it a text which will be interesting, instructive and comprehensive. To the lieutenants in charge of Department “A” and to those who aspire to that responsibility it is hoped that this work will prove a valued addition to their professional libraries.

The subjects covered herein have been taken wholly or in part from the various official handbooks, from “Ordnance and Gunnery, U. S. M. A.,” “Naval Gunnery, U. S. N. A.,” “America’s Munitions,” “Gun Making in the U. S. A.,” “Ordnance and Gunnery for Field Artillery Officers,” “Artillery Firing,” “The Field Artillery Journal,” Ordnance Doc. 2033, from lecture notes taken at the School of Fire, Brigade Training Pamphlets, and various other sources.

The compiler is indebted to Lt. Col. Lloyd E. Jones, F. A. and Major H. C. Jackson, F. A. for the valuable advice and the helpful assistance they rendered in this compilation.

CONTENTS.

LIST OF ILLUSTRATIONS

CHAPTER I
DEFINITIONS.

In the study of any subject which is rather technical in nature, it is absolutely essential that the reader be familiar with the meaning of the words and phrases which must be used in the matter to be discussed. If the subject matter is to be understood there must be a common phraseology. The reader is therefore strongly urged to perfect his knowledge of the following short vocabulary before passing on to the matter which follows.

Ammunition. A general term applied to all forms of powders, shells, cartridges, primers, etc.

(a) Fixed Ammunition. When the powder charge is enclosed in a metallic container which is fixed to the projectile, it is called “Fixed Ammunition.”

(b) Semi-Fixed Ammunition. When the charge and metallic container are a fixed unit but are not fastened to the projectile, it is called “Semi-Fixed Ammunition.”

(c) Separate Ammunition. When the powder charge is contained in bags separate from the projectile and containing not a fixed but a varying charge, it is called “Separate Ammunition.”

Artillery. All firearms not carried by hand, excepting machine guns. It is divided into two general classifications: (1) artillery of position, and (2) mobile artillery.

(1) Artillery of Position is that which is permanently mounted in fortifications.

(2) Mobile Artillery consists of two classes: first, artillery designed to accompany an army in the field; second, railway artillery which requires tracks for its transportation.

Ballistics. The science of hurling projectiles or of the motion of projectiles in their flight.

Bore. The hole which extends from the muzzle to the breech. The passageway for the projectile. That part of the tube which is bored out.

Breech. The rear end of the gun, tube, or barrel.

Caisson. A two-wheeled vehicle which supports an ammunition chest. The wheeled equipment of a gun section consists of one gun with its limber and one caisson with its limber. For a caisson section it consists of two caissons with their limbers.

Caliber (Calibre). The diameter between the highest points in the bore.

Carriage, gun. Usually understood to mean all the piece except the tube with its appurtenances and the limber.

Cartridge case. A hollow cylinder shaped to fit the bore. A container for the propelling charge.

Charge.

(a) Propelling. A quantity of powder used in the bore to generate the gases which propel the projectile from the gun.

(b) Bursting. A quantity of powder used in shrapnel to strip off the head of the projectile and to force out the balls.

(c) Explosive. The matter used in a shell to detonate it at the end of its flight.

Cradle. In general, that part of the carriage which houses the recoil and counter-recoil mechanisms.

Elevating Mechanism. The device used to elevate the gun through a vertical arc in order to give the gun an elevation corresponding to the desired range at which the piece is to be fired.

Fire Control Equipment. Those instruments used to compute firing data, observe and correct the fire, such as B. C. Telescopes, Aiming Circles, Range Finders, etc.

Firing Mechanism. A device located in the breechblock for exploding the primer and thus causing the ignition of the powder charge.

Fuze. That part of the round which is fastened to the point or to the base of the projectile and causes the latter to be detonated or exploded near the time or the place desired.

Fuze Setter. A device used to set time fuzes in such a manner that shrapnel or shell will burst at or near the desired height in air.

Gun. A metallic tube from which projectiles are hurled by gases generated from the ignited powder. In general, all fire arms; but in Field Artillery terms, comparatively long-barreled weapons using relatively high muzzle velocity in contra-distinction to the howitzers and mortars.

Howitzer. A weapon which differs from a gun in that for the same caliber it uses a shorter tube, lower muzzle velocity and generally a more curved trajectory. From two to seven varying strengths of propelling charges may be used in the howitzer. This gives it selective angles of fall, and allows the howitzer to reach targets that are hidden from the flat trajectories of guns.

Initial Velocity. The speed with which the projectile first moves.

Limber. A two-wheeled carriage which is sometimes used to carry an ammunition chest and always used to support the weight of the trail of the piece or caisson. It adds the other two wheels to make a four-wheeled vehicle.

Materiel. A term used in the Field Artillery in contra-distinction to Personnel.

Mortar. A weapon using for the same caliber, a barrel much shorter than the corresponding howitzer. Used at short ranges with extreme steep angles of fall to reach highly defiladed targets.

Muzzle. The front end of the bore.

Muzzle Velocity. Speed or velocity of the projectile measured as it leaves the muzzle.

Ogive. The rounded shoulder of the projectile.

Ordnance. Arms, ammunition, and their accessories.

Piece. A fire arm, small or large.

Primer. Device used to insure ignition of the propelling charge.

Projectile. The effect-producing part of the round. The bullet-like form which is thrown toward the target.

Quadrant, gunners. A device for measuring angles of elevation.

Recoil Mechanism. That part of the piece which checks the recoil—or kick—that always occurs when a piece is fired. It generally includes the counter-recoil mechanism which restores the tube “into battery” after it has fired.

Rifle. A gun. A weapon with a comparatively long barrel and high muzzle velocity. Rifles under 6 inches seldom use over two different charges. Term used in contrast to Howitzer or Mortar.

Rifling. The lands and grooves in the bore of the piece which imparts to the projectile during its passage through the bore, the rotary motion that increases accuracy and range.

Round. Consists of the primer, cartridge case or powder bags, projectile and fuze. For light Field Artillery the round weighs about 18 lbs and the projectile about 15.

Shell. A projectile which secures its effect by the force of its detonation, the bursting of its walls, and the fragmentation and velocity of the fragments. Also used as a gas carrier.

Shrapnel. A projectile which secures its effect by the expulsion in the air of lead balls with shot-gun like effect.

Trail. That part of the piece which extends from the axle to the rear and transmits the force of recoil to the ground through the trail spade. Usually supports the elevating and traversing mechanisms.

Traversing Mechanism. A device used to give the piece direction by moving it through a horizontal arc.

CHAPTER II
HISTORY AND DEVELOPMENT OF MATERIEL.

In taking up the study of materiel, the Field Artillery student should know something of the history and development of ordnance and the reasons for the various changes which have taken place from time to time.

The sole use of a gun is to throw a projectile. The earliest projectile was a stone thrown by the hand and arm of man—either in an attack upon an enemy or upon a beast that was being hunted for food. Both of these uses of thrown projectiles persist to this day, and, during all time, from prehistoric days until the present, every man who has had a missile to throw has steadily sought for a longer range and a heavier projectile.

In ancient times the man who could throw the heaviest stone the longest distance was the most powerfully armed. During the Biblical battle between David and Goliath, the arm of David was strengthened and lengthened by a leather sling of a very simple construction. Much practice had given the youthful shepherd muscular strength and direction, and his stronger arm and straighter aim gave him power to overcome his more heavily armed adversary.

Projectile-throwing machines were developed after the fashion of a crossbow mounted upon a small wooden carriage which usually was a hollowed trough open on top and upon which a stone was laid. The thong of the crossbow was drawn by a powerful screw operated by man power, and the crossbow arrangement when released would throw a stone weighing many pounds quite a distance over the walls of a besieged city or from such wall into the camps or ranks of the besiegers. This again was an attempt by mechanical means to develop and strengthen and lengthen the stroke of the arm and the weight of the projectile. The Bible states that King Usia (809-757 B. C.) placed types of artillery on the walls of Jerusalem. The Romans used it in the Punic Wars. The Alexandrian technicians established scientific rules for the construction of early weapons. Athenaeus reports catapults having a range of 656 meters and that the gigantic siege tower at Rhodes successfully resisted stone projectiles weighing 176 pounds.

References to explosives are to be found in works as old as Moses. Archimedes is said by Plutarch to have “cast huge stones from his machines with a great noise;” Caligua is said by Dion Cassius to have had machines which “imitated thunder and lightning and emitted stones;” and Marcus Graecus in the eighth century gives a receipt of one pound of sulphur, two of willow charcoal and six of saltpetre, for the discharge of what we should call a rocket.

The use of Greek fire was understood as early as the sixth century, but powder was earliest used in China, perhaps a thousand years before Christ, and was introduced to European notice by the Saracens.

From the discovery of gunpowder by the English monk Bacon in 1248, sixty-five years elapsed before a Franciscan monk produced the first gun in Germany, about 1313. The first guns were of a small breech-loading type, supported in front by crossed sticks and anchored by a spike at the breech. Later these guns were fastened to cradles, the latter being mounted on sleighs, and finally, in 1376, the Venetians produced the first wheel mounts, which had become common by 1453, when the Turks took Constantinople.

The ancient carriages were remarkable because of the fact that in general design they embodied the same principals which are included in the field carriages of to-day. One example from the fifteenth century shows a breech-loading gun mounted in a cradle supported by trunnions on the forward extension of the trail over the axle. The cradle was elevated by a pin-and-arc arrangement, supported on the trail. The axle supported by wheels passes through the trail to the rear of and below the cradle trunnion support and in front of the point of attachment of the elevating arc.

Field guns fell into disuse about 1525 with the introduction of musketry, and remained so until 1631, when Gustavus Adolphus gave artillery its true position on the battlefield.

Swedish artillery reigned supreme in the early part of the seventeenth century. Gustavus introduced marked changes by making the guns and the carriages lighter and handier, and by adapting their movements to those of the other arms and to the requirements of the battlefield. In this, as in all his military efforts, his motto was mobility and rapidity of fire.

In 1624 Gustavus had all his old types of guns recast into newer models and the following year he himself contrived a gun which three men and one horse could maneuvre to good effect. It was an iron three and four pounder with a cartridge weighing less than a pound and consisting of a charge held in a thin wooden case wired to a ball. This was the first artillery cartridge, the original fixed ammunition. The gun was afterwards used in other European armies and known as the “piece Suedoise.” Not only had it the advantage of lesser weight but its cartridge was always ready to fire and it could be fired eight times to the six times of the infantry musket of that day.

In the wars against the Poles, Gustavus employed with profit the so-called leather cannon, a fact which shows how lacking the times were in artillery power. These guns were invented in the early 1620s by a Colonel Wurmbrandt, and consisted of a thin copper tube reinforced by iron bands and rings, then bound with rope set in cement, the whole covered with sole leather. The tube was made to screw in and out because it grew heated by from eight to twelve charges and had to be cooled. The gun carriage was made of two planks of oak. The gun without the carriage weighed about ninety pounds and was fired with a light charge. They were used during 1628-29 and then gave way for four pounder cast-iron guns which remained in common usage in Europe until artillery was reorganized by Frederick.

Gustavus’ batteries excited universal admiration. Grape and canister were generally employed in the field guns and round shot only in the siege guns. Artillery was used massed or in groups and also with regiments of foot soldiers. Gustavus was probably the first to demonstrate the real capabilities of artillery.

Mortars throwing bombs were first used at the siege of Lamotte in 1634. Hand grenades, shells, fire-balls, etc., came into more general use as the German chemists made their new discoveries. Artillery practice grew to be something of a science; experts took it up and the troops were better instructed. Regimental artillery, that is, artillery with the infantry, was attended by grenadiers detailed for the work. There were special companies for serving the reserve guns.

The period following the Thirty Years’ War—the middle of the seventeenth century—gave no great improvement to the art of war but there were many marked advances in the matter of details of construction. During the era of Gustavus it was Sweden that led in making war more modern; during the era of Louis XIV it was France.

Artillery ceased to be a guild of cannoneers as it long had been and became an inherent part of the army. More intelligence was devoted to it and more money spent on this arm of the service; it grew in strength and importance, and was markedly improved. But while the artillery service ceased to be a mere trade, it did not put on the dignity of a separate arm, nor was the artillery of any great utility in the field until well along in the eighteenth century. Guns, however, in imitation of the Swedes, were lightened, particularly so in France; powder was gradually compounded on better recipes; gun-metal was improved; paper and linen cartridges were introduced; gun carriages were provided with an aiming wedge; and many new styles of guns and mortars, and ammunition for them were invented.

Science lent its aid to practical men, and not only exhausted chemical ingenuity in preparing powder and metal, but mathematical formulas were made for the artilleryman, and value of ricochet firing was discovered. Louis XIV founded several artillery schools, and initiated the construction of many arsenals. Fontainebleau, the French artillery school which trained many Americans during the World War had its beginning in this period. Finally, the artillery was organized on a battery and a regimental basis, and careful rules were made for the tactics of the guns. These were served by dismounted men and generally hauled by contract horses.

Although sensibly improved, the artillery was far from being skillfully managed and was slow firing; it usually stood in small bodies all along the line of battle. It was heavy and hard to handle and haul, principally because the same guns were used for both siege and field work, and was far from being, even relatively to the other arms, the weapon which it is to-day.

In 1765 General Gribeauval of France introduced artillery improvements, especially in the carriages, and formed a distinct artillery service for the field which was lighter than the old service and was drawn by teams which were harnessed double as they are to-day.

Howitzers were introduced in France in 1749. The weapons were given an early sort of perfection by the Dutch. The term “howitzer” comes from the German “haubitz.” In 1808 the first shrapnel appeared at Vimera. It was invented by an English colonel by the name of Shrapnel. At the time it was known as case shot. The type employed by Napoleon, had a fuze that could be used at two different ranges. The French still have this type in their armament.

Field artillery now began to appear in the form which it was to retain with but a few changes, until the era of the modern field carriage. The cradle disappeared, muzzle-loading guns cast with trunnions taking its place, and a stepped wedge resting on the trail superseded the pin and arc. With the exception of the gun, most parts of these carriages were of wood and were to remain so until 1870, when metal carriages came into general use. Muzzle loading guns had supplanted breech-loaders because of the poor obturation and the many accidents resulting from use of the latter type. Although numerous experiments were made, breech-loading guns did not come into vogue again until 1850, when the experiments of Major Cavalli (1845), the Walnendorff gun (1846) and the Armstrong gun (1854), produced satisfactory types.

Up to 1860 practically all guns were smooth bore. Even during the Civil War the smooth bore was generally used, although the rifled gun began to make an appearance and was used in small numbers by both sides at the battle of Gettysburg. Some breech loaders began to appear at the same time. Improvement in the ballistic properties of the gun necessitated a corresponding improvement in the sighting facilities. In 1880 rifled breech loading and built-up steel cannon came into general use. Rifled guns shoot accurately and as a result, improved methods in direct laying were devised.

The period between from 1880 to the present, has brought about changes in gun construction which, possibly, have been equaled in importance to artillery only by the present change which is taking place in the means of artillery transportation and self-propelling mounts. In this period in rapid succession came the modern breechblock and with it the rapid firing gun. This brought about the change to the present system of breaking the force of recoil of the gun and restoring it to its firing position without disturbing the position of the carriage. This added to the possibilities of rapid and more accurate fire. Then came the invention and use in the field artillery of smokeless powder. Previous to this time the great amount of smoke produced by the black powder when the piece was fired retarded the rapidity of fire because it enveloped the materiel in a thick cloud of smoke which obscured the target and made it impossible to fire again until the smoke had blown away. It made concealed positions for the artillery almost impossible. The advent of smokeless powder made firing more rapid and made possible the selection of concealed positions. This in turn made indirect fire feasible and necessitated the development of better sights. Indirect fire increased the rapidity of fire and gave to the commanders of firing units a greater control over their fire. With the use of recoil mechanisms and shields for the guns, the cannoneers were permitted to serve the piece continuously—a condition which was impossible with the recoiling carriage. The shields made it almost impossible to put the gun out of action unless some vital part of the mechanism was destroyed.

The first of the modern carriages which were produced in the early nineties should be classified as semi-rapid carriages, as the recoil brakes were so abrupt that the carriage was not stable and jumped considerably, gaining for the type the sobriquet of “grass-hopper guns.”

In 1897 the immortal French “75” was born, the pioneer of all modern quick-firing field guns, which still maintains its superiority in many respects over later designs.

In 1902 our own 3-inch field gun was produced and still finds favor among many of our field artillery officers, even over the French “75.”

The Deport carriage brought to this country from Italy, in 1912, introduced to us the split trail, high angle of fire, wide traversing type of field gun carriage. This carriage was extensively tested by the Ordnance Department; by the Field Artillery Board at Fort Riley, Kansas; and by the School of Fire for Field Artillery, at Fort Sill, Oklahoma. The Field Artillery Board unqualifiedly approved of the Deport carriage and recommended that it be adopted. The School of Fire for Field Artillery also approved of this type.

In 1916 the United States produced a 75-mm field gun which featured a split trail with an elevation of 57 degrees which permits its use as an anti-aircraft weapon and a variable length of recoil which prevents the breech from hitting the ground at the extreme elevations. It has a traverse of 800 mils in comparison to the 106 of the French 75 and the 142 and 140 of the British 75 and American three-inch field gun.

The outbreak of the late war saw all modern armies largely equipped with guns resembling the French “75” in a long-run recoil mechanism, weight of projectile and weight of carriage, etc. The fact that the largest number of horses which could best be handled to maneuver the light guns—about 6—could not pull over a long period a gun or caisson with its limber if the weight was more than about 4500 pounds, resulted in the practical standardization of light guns in all armies. So in 1914 we see that time and development had given light gun perfection and mastery of artillery technique to the French while the Germans, probably, possessed the most efficient artillery program. The German types of weapons were more varied and perhaps better suited to the varying artillery needs in rendering that assistance to the infantry for which the artillery exists.

In our service during the World War, French 75s and the 155-mm Howitzer were used as divisional artillery. Two regiments of the light guns and one regiment of 155-Howitzers were assigned to each infantry division. As the war progressed guns and howitzers ranging from the 4.7” rifle, up to, and including 14 and even 16-inch naval guns on railroad mounts, were used as Corps and Army artillery.

Thus artillery development has gone steadily forward. Every military power has striven with the aid of its best engineers, designers and manufacturers to get a stronger gun, either with or without a heavier projectile, but in every case striving for greater power. As a special development and a not too important one, due to its lack of effectiveness in comparison to its cost, we find the now famous long range gun of the Germans, successfully delivered a projectile approximately 9 inches in diameter into Paris punctually every twenty minutes from a point about 75 miles distant. The Germans used three of these guns in shelling Paris. Their life was probably limited to about 75 rounds due to the excessive demands made upon the materiel.

The American Field Artillery Service now has before it four types of field gun carriages, namely our 3” model of 1902; the French 75 M-1897; the British 18 pounder, M-1905 converted to a 75-mm (known as the model of 1917); and our 75-mm model, 1916. There is being produced (1919-20) an improved model of 1916 75-mm carriage on which the St. Chamond pneumatic recuperator, adopted jointly by the American and French governments, will be substituted for the spring recuperators; and the French 75-mm gun will be substituted for our shorter calibered type. From these types one must be selected. An intelligent selection involves a consideration of what may be expected in the future in order that it may best fit in with the new types yet to be evolved.

For horsed artillery—and horse artillery will be with us for some years to come—the limiting features of draft and man power will still pertain.

For tractor-drawn mobile artillery, the limiting feature is the tractive power of the tractor with relation to the weight of the gun and carriage, the unit being physically limited in weight by the supporting-power of the pontoon bridge which is about 10,000 pounds per vehicle.

For Caterpillar Artillery.—By that is meant guns mounted on caterpillar tractors—the limiting features are power and weight, coupled with the weight limitations of the pontoon bridge. To circumvent the question of weight, the load may be divided by mounting the motor by an electric generator on one caterpillar and the gun with an electric motor, on the other, a transmission cable connecting the two vehicles.

In conclusion it might be said that one of the greatest changes which has ever taken place in the development of field artillery is now underway in the form of motorization. Prior to 1917 horse traction had been the sole means of transporting mobile field artillery. The limit of the capabilities of horse traction placed a weight limit upon gun construction and to some extent upon artillery tactics. The increase in the ratio of field artillery to infantry, the corresponding demand for artillery types of horses and the decrease in the availability of the latter as the war continued, combined with the great improvements which were constantly being wrought in mechanical transportation as the war lengthened, opened the way for artillery motorization.

The French began by placing their 75s on trucks for rapid changes of position. All the armies saw the possible advantages to be gained from the use of trucks with artillery but none planned—nor have any since put into practice—the extensive use of trucks, caterpillar tractors and motor transportation for personnel, which the United States planned on her entrance into the war. It was planned to equip about one-third of the A. E. F. artillery regiments with complete motor equipment. This plan did not entirely materialize but after the armistice the 3rd Field Artillery Brigade of the 3rd Division was completely motorized and its practice marches in Germany were most successful and full of promise for the future. To date the motorization of all our mobile Field Artillery, with the exception of about fifty per cent of the light field guns, has been authorized.

Motor traction gives a better performance than animal. While the latter, especially with the light field guns, possesses great mobility, it is not a sustained nor a persistent mobility; it is more easily exhausted and requires longer to recuperate. These are points of vital importance from a military viewpoint.

In 1920 a self-propelling caterpillar mounted with a 75-mm gun, model 1916, was tested with a view to ascertaining the ability of the motor to function in water, i. e. fording streams, etc. The caterpillar successfully moved through ice water which completely submerged the carburetor.

Passenger cars for the transportation of personnel, four wheel drive trucks with caterpillar tractors for the transportation of the materiel, and the development of self-propelling mounts for the 75 and 155 rifles are the latest and the most important developments in field artillery materiel.

CHAPTER III
ELEMENTS OF GUN CONSTRUCTION AND DESIGN

“A gun is a machine by which the force of expanding gas is utilized for the purpose of propelling a projectile in a definite direction.” It is essentially a metal tube closed at one end, of sufficient strength to resist the pressure of the gases caused by the combustion of the powder charge in the confined space at the closed end of the tube behind the projectile. The rapid combustion of the powder, which produces a high temperature, gives rise to a pressure uniformly exerted in all directions within the confined space. The energy exerted is used in forcing the projectile from the tube.

TUBES

Due to the effort of the large amount of superheated gas generated, which tends to expand in all directions, tremendous rending stresses are set up in the tube. Formerly these stresses were met by a sheer mass of metal, but, as the size of the projectiles increased and the necessary pressure to give them muzzle velocity increased, the size of the guns increased beyond the practical limits of mobility. This was at first offset by forgings of refined alloyed steels, but even these failed to keep pace with the increasing pressure desired. The new condition was met by the introduction of the “built-up” and the “wire-wrapped” guns. The modern built-up gun is made by assembling one or more superimposed cylinders around a central tube. The superimposed cylinders, whose inside dimensions are slightly smaller than the outside dimensions of those on which they are to be assembled, are expanded by heat sufficiently to allow them to be assembled over the tube. The subsequent contraction on cooling causes each of them to exert a uniform pressure on the cylinder immediately underneath. This method of assembling is called “shrinkage.” This gives a compression to the inner tube and a slight tension to the outer one. The compression is so much additional strength to the tube because it must first be overcome before the powder gases can exert a tension on the inner tube fibers. The exact amount of the compression and tension for all parts of a gun at rest or resisting an explosion is a matter of mathematical calculation. The built-up construction has been used in practically all our present day types of field artillery.

THE WIRE-WRAPPED GUN.

Wire-wrapped guns consist of:

(a) An inner steel tube which forms a support on which the wire is wrapped and in which the rifling grooves are cut.

(b) Layers of wire wrapped upon the tube to increase its resistance by the application of an exterior pressure as well as to add to the strength of the structure by their own resistance to extension under fire.

(c) One or more layers consisting of a steel jacket and hoops placed over the wire with or without shrinkage. The jacket generally furnishes longitudinal strength to the guns, and the breech block is screwed into the jacket, or into a breech bushing, which is screwed into the jacket.

The principal advantages of this type of gun over the built-up is economy of manufacture and greater facilities for inspection of materiel in the layers over the tube. The wire wrapping has itself a large reserve of strength due to the high elastic limits that may be given it. Two methods are used to wrap the wire: (a) at constant tension (b) at varying tension so that when the gun is fired with the prescribed pressure, all layers of wire shall be subjected to the same tangential stress. The latter method is theoretically better, but because of the ease of manufacture, together with the large factor of safety possible, the wire is usually wrapped at a constant pressure.

THE BUILT-UP GUN.

All army guns except small howitzers or mortars are of the built-up or wire-wrapped type. Built up guns of less than 5” caliber, or howitzers up to 8” caliber consist of an inner tube and a jacket shrunk onto this tube. The jacket covers the breech end of the gun and extends forward to the center of gravity. Built-up guns of larger caliber have one more layer of hoops in addition to the jacket, one layer of hoops usually extending to the muzzle.

The bore of the tube forms the powder chamber, the seat for the projectile and the rifled bore. Rifling consists of a number of helical grooves cut in the surface of the bore. The soft metal of the rotating band of the projectile is forced into these grooves causing the projectile to take up a rotary motion as it passes through the bore. This is necessary in order to keep the projectile stable in its flight.

TWIST.

By twist of rifling is meant the inclination of one of the grooves to the element of the bore at any point. Rifling is of two kinds: (a) Uniform twist, or that in which the twist is constant throughout the bore, (b) Increasing twist or that in which the twist increases from the breech towards the muzzle.

The twist of rifling is usually expressed in the number of calibers length of bore in which it makes one complete turn. The twist actually required at the muzzle to maintain the stability of the projectile varies with the kind of projectile and the muzzle velocity. If a uniform twist be used, the driving force on the rotating band will be at a maximum when the pressure in the guns is at a maximum—or near the origin of rifling (seat of the projectile). The increasing twist serves to reduce the maximum driving force on the band thus lessening the danger of stripping the band. This is its principal advantage over the uniform twist, though it also reduces slightly the maximum pressure in the gun. The principal disadvantage of the increasing twist is the continued change in form of the grooves pressed in the rotating band, as the projectile passes through the bore. This results in increased friction and a higher value for the passive resistance than with a uniform twist. (Note: greater ranges obtained by cutting grooves in projectile, principal used on the long range gun by the Germans.) If the twist increases from zero at the breech uniformly to the muzzle, the rate of change in the tangent to the groove is constant. A twist in this form offers less resistance than the uniform twist to the initial rotation of the projectile. To still further diminish this resistance a twist that is at first less rapid than the uniformly increasing twist and later more rapid has been generally adopted for rifled guns.

Formerly in our service the twist was uniform; one turn in 25 calibres for guns and one turn in 20 calibres for howitzers. All the latest model army guns, however, have an increasing twist of one turn in 50 calibres at the breech to one turn in 25 calibres at a point from 2 to 4 calibres from the muzzle. In howitzers and mortars the twist is sometimes one turn in 40 calibres at the breech to one turn in 20 calibres at a point several calibres from the muzzle. Some mortars are rifled with a uniform twist and some guns have a rifling which begins with a zero twist. (The 1905 3” gun, 0 to 1 in 25.)

OUTER CYLINDERS.

Outside of the tube is the jacket. It extends to the rear of the tube a sufficient distance to allow of seating the breech block. In this manner the longitudinal stress due to the pressure of the powder gases on the face of the breech block is transmitted to the jacket thus relieving the metal of the tube from this stress. In all built-up guns there is some method devised for locking the tube to the jacket so as to prevent relative movement of these parts.

Considering the gun alone the greatest range is obtained at an angle of about 43 degrees from that gun which fires the heaviest projectile with the greatest velocity. The caliber being limited to from 2.95 inch to 3.3 inch, the projectile is limited in weight to from 12 to 18 pounds. The weight of the gun is limited to between 700 and 1000 pounds and in length to between 27 and 36 calibers. The longer the gun, the greater the weight and velocity from the same charge of powder. A pressure of 33,000 pounds per square inch with a corresponding velocity of 1700 f. s. has been found to be as high a pressure and velocity as are desirable for a reasonable length of life for a field gun, the average life of which is 10,000 accurate rounds.

Under the French school of artillery, which dominates our service at present, our bore is 75-mm, the weight of our shell 12 pounds, our shrapnel 16 pounds, the velocity for the one about 1,750 f. s. and for the other about 1,680 f. s.

BREECHBLOCKS.

The breechblock appears in four distinct types. Our own service has for years used the swinging interrupted screw breechblock which in the 1905 model is the equal of any of that type in existence. The swinging block has serious disadvantages for high angle fire in that it requires an excessive amount of room to operate and is difficult to load at high elevations.

The Italians have introduced a new breechblock in one of their recent guns, consisting of a half cylinder with superimposed spherical face on its cylindrical surface rotating vertically about a horizontal axis perpendicular to the axis of the bore. The gun is loaded through a groove in the breechblock when the latter is in its horizontal position. The block, which is semi-automatic, is very satisfactory. It is adapted to high angle fire.

The French in their “75” have used the rotating eccentric screw type, which is rapid in movement and lends itself fairly well to high angle fire. It is completely enclosed and of rugged construction.

The Germans have used the sliding wedge type of block, moving in a horizontal direction, which does not lend itself to high angle fire.

The United States in its recent field carriage adopted the sliding wedge type in a vertical plane on account of its manifest superiority in fire at high angles. This block is rather difficult to manufacture and the type has a tendency to stick. The automatic closing necessitates a strong closing spring which fatigues the block operator, No. 1 in the gun squad. It is interesting to note that in a prospective new design for the 1916 gun carriage the American Ordnance Department adopted the French breechblock; and the St. Chamond Company, designing for the American Expeditionary Forces, adopted the American drop block.

Requirements for a breech mechanism:

The following may be said to be the principal requirements for a successful breech mechanism.

1. Safety. To be safe: (a) the gas must be restrained from escaping to the rear; this sealing or obturation must be automatic, greater pressure insuring better obturation. (b) The breech of the gun must not be weakened by the fitting of the breech mechanism. (c) The parts must have ample strength to prevent any portion from being blown to the rear. (d) The danger of premature discharge must be minimized. (e) The breechblock must be securely locked to prevent opening on firing.

2. Ease and Rapidity of Working. Otherwise, rapid and continuous fire cannot be maintained. Hence this would include facility in loading and certainty of extraction for rapid fire guns.

3. Not Easily Put Out of Order. In other words it must be able to meet service conditions and hard usage. Parts should have a reserve strength.

4. Ease of Repair. Parts most exposed to wear should be so designed as to permit being replaced. This will also include accessibility to parts, so that breakage of a part will not disable the mechanism for a long time.

5. Interchangeability. Not only should individual parts be made interchangeable by accurate workmanship, but the whole mechanism should be capable of being mounted on similar guns. This is to meet service conditions.

GUN CARRIAGES.

A modern gun carriage is expected to stand steady on firing, so that in the first place it requires no running up, and in the second place it maintains the direction of the gun so that only a slight correction in elevation and direction is required after each round. The carriage is maintained in position by the spade, which sinks into the ground, and by the friction of the wheels upon the ground. If the force of the recoiling gun were communicated directly to the anchored carriage the effect would be to make it jump violently, which would not only disturb the lay, but would prevent the cannoneers from maintaining their position. The hydraulic recoil brake is therefore interposed between gun and carriage. If the guns were rigidly attached to the carriage the latter would be forced back a short distance at each round, and the whole of the recoil energy would have to be absorbed in that short motion. Instead of this the gun alone is allowed to recoil several feet and although the recoil energy is in this case greater than it would be if gun and carriage recoiled together yet it is so gradually communicated to the carriage that instead of a violent jerk we have a steady, uniform pull, the only effect of which is to slightly compress the earth behind the spade. In a well designed carriage the amount of this pull is always less than that required to lift the wheels off the ground by rotating the carriage about the spade.

The only motion of the carriage which takes place is that due to the elastic bending and rebound of its parts under the cross strains set up on discharge. These strains are inevitable since the direction of recoil cannot be always exactly in the line of the resistance of the earth behind the spade. This movement of the axis is known as jump and must be determined by experiment for the individual piece in its particular mounting.

The principal parts of the typical gun carriage are the cradle, a device for mounting the cradle—called in the different models rocker, pintle yoke, and top carriage, the trail, the wheels and axle. The gun slides in recoil on the upper surface of the cradle and the cradle contains the recoil controlling parts.

In the design of the carriage the constructional difficulty lies not so much in preventing the carriage from recoiling but in preventing the wheels from rising off the ground on the shock of discharge. The force of the recoil of the gun, acting in the line of motion of the center of gravity of the recoiling parts, tends to turn the carriage over backwards about the point of the trail or center of the spade. This force is resisted by the weight of the gun and carriage, which tends to keep the wheels on the ground. The leverage with which the overturning force acts is due to the distance of its line of action above the center of the spade; the leverage with which the overturning force acts is that due to the horizontal distance of the center of gravity of the gun and carriage from the center of the spade.

It follows that the steadiness of the carriage for a given muzzle energy may be promoted by four factors.

(a) Increasing the weight of the gun and recoiling parts. This reduces the recoil energy.

(b) Increasing the length of recoil allowed. This reduces the overturning pull.

(c) Keeping this gun as low as possible either by reducing the height of the wheels, or by cranking the axle downwards. This reduces the leverage of the overturning force.

(d) Increasing the length of the trail. This increases the leverage of the steadying force.

The well designed gun carriage is one that combines these factors in a practical way so as to give the greatest possible steadiness to the carriage at the same time keeping within the limits of weight imposed by the necessity of mobility.

Gun carriages are constructed so as to permit movement of the tube in the vertical and generally in the horizontal plane. These two motions may be made simultaneous if so desired by proper combination of the two motions and the axis of a gun aligned in any desired direction within the limits of motion of its mount. The two motions referred to are designated as follows: (a) Rotation of the piece about a vertical axis, its inclination with the horizontal remaining unchanged is called “traverse.” (b) Movement of the piece in a vertical plane, the direction of the horizontal projection of the axis of the bore remaining unchanged is called “elevation.”

In order to permit of the two motions mentioned, gun carriages are provided with mechanisms for giving the piece accurately controlled motion in both elevation and traverse. The elevating gear of most American guns is an application of the Chinese or Telescopic screw. This gives a short assembled length with the necessary extended length required for modern ranges. It also gives the necessary rapidity for action. An entirely different mechanism is used in our howitzers and American 75s. In this case motion is communicated to the rockers, which carry the gun and cradle, through the engagement of worms with teeth cut on the lower circular edge of the rockers, the latter being pivoted on the cradle trunnions.

TRAVERSING MECHANISMS.

Movement of the gun in traverse is accomplished in two general ways.

(a) Pivot on the gun carriage axle.

1. The gun and cradle move around a vertical pintle or pivot placed in a saddle or rocker which itself pivots on horizontal trunnions or bearings usually attached to the axle. The rear end of the rocker forms a seat or bearing on which the cradle and gun move in traverse. The upper end of the elevating screw is also attached to the rear end of the rocker. This allows the rocker and cradle to be moved together in elevation and the cradle to move on the rocker in traverse.

2. The gun and cradle are mounted by means of horizontal cradle trunnions on a top carriage. The top carriage moves in traverse around a vertical pintle or bearing attached over the axle and between the front end of the trail flasks. The rear end of the top carriage moves on bearings attached to the top of each side of the trail flasks. This allows the gun, cradle and rocker to move in elevation with respect to the top carriage and the top carriage bearing the gun, cradle rocker and elevating mechanism to move in traverse with respect to the bottom carriage.

(b) The gun, cradle and trail move in traverse by sliding along the axle of the carriage on bearings provided for that purpose. In this case the trail spade is the point of pivot.

The first system is the one generally used on all American gun carriages except the 155-mm Howitzer. It gives ease and speed in the manipulation of the piece in traverse, but has the disadvantage of rendering the carriage less stable in firing due to the fact that the direction of recoil of the gun is in the direction of the line joining the trail spade and the central pivot, only when the gun is absolutely in the center of its traverse. In all other positions, which will be the usual case, there is a component at right angles to the line of trail spade-central pivot which tends to throw the gun off from its proper direction making it necessary to relay each time the gun is fired. The second method is that in use on the French 75-mm gun and the French and American 155 howitzer. While not so easy of manipulation and giving less freedom of movement in traverse (about 106 mils) it still has the advantage in that it gives greater stability in firing due to the fact that the gun always recoils along the line through the trail spade, perpendicular to the axle.

ELEVATING MECHANISMS.

There are two general classifications of gun carriages according to the manner in which the laying for elevation is effected. The 3” gun is an example of one type in which the total quadrant angle of departure is laid off as one angle necessitating at each resetting of a range a new resetting of the range bubble. It is evident that this militates against both speed and accuracy in laying for elevation. The other type is illustrated by the American 75 and by the French and British 75-mm gun carriages which have what is called the “independent line of site.” It differs from the other type in that there is placed between the top carriage and the cradle an intermediate carriage or rocker arm pivoting on the gun trunnions at one end, and carrying at the other the support for the elevating device which gives to the cradle and the gun the proper elevation for the range. This intermediate carriage or rocker arm has a toothed edge geared with a pinion fastened to the trail flask, by means of which, gun cradle and elevating device may be moved in elevation without disturbing the relation between itself and the gun, this being done by gears independent of the elevating mechanism. An angle of site may be set off for the intermediate carriage and after the bubble is centered this actuating pinion may be blocked and no further concern be paid to the angle of site. A cannoneer therefore has only to set his range accurately on the index to give the changes in range ordered.

Elevation is accomplished by telescoping screws, by circular racks and pinions, and by worms and arcs. Telescoping screws are good for from 15 to 20 degrees in elevation only, as for greater angles they become rather too large and cumbersome. The elevating arc is attached on the top, on the bottom or on the side of the cradle and, if possible, at its center. When the latter is not possible, two arcs are generally used to prevent torsional strains developing. Top racks are exposed to fire, side circular racks or arcs interfere with the traverse, with the placing of the sights, and with the general handling of the carriage. The bottom of the cradle is perhaps the best location for the rack. As in the traversing mechanism, a train of bevelled gears transmits the power from the hand wheel to the elevating mechanism.

In both the traversing and elevating mechanism, strength, simplicity, power, accessibility, non-interference and absence of lost motion are the features sought. To secure these is one of the most difficult things in gun-carriage design; for, since the traversing and elevating are the last two elements considered, they must, therefore, be the ground for modification and the means of adapting the great main elements—namely, wheels, axle, trail, recoil mechanism and gun—into a unit.

RECOIL MECHANISM.

The recoil system of the gun carriage consists of a recoil brake, a counter recoil mechanism and a counter recoil brake. The function of each part is apparent from its name. Various systems of checking recoil on field guns have been used, among them may be mentioned; friction devices including brakes on the wheel, inclined planes, pneumatic and hydraulic brakes. All have either been superseded by the last named or are used in connection with hydraulic brakes. The power of the brake lies in the pressure produced in the cylinder through the resistance to motion offered by the liquid flowing through apertures. By varying the size of these apertures the braking effect may be controlled so as to fulfill the conditions demanded by the service. In designing the brake, the effect of the counter recoil system, angle of fire, length of recoil, friction and pressure within the cylinder must all be considered. In howitzers which are designed to be fired at high angles of elevation, the recoil must be shortened to prevent the breech striking the ground, a condition successfully met. Since the pressure due to recoil is ultimately led into the ground through the trail and spade, consideration must be given to the problem of the moment of inertia about the trailspade. The tendency to turn over backward about the spade as the center is offset by the amount of the weight of the carriage with respect to the same point. This raises the question as to how much pressure may be allowed to act to the rear; all of which must be considered in designing the carriage. The counter recoil systems in general use are two: spring or pneumatic. The former is illustrated in our 3” and 75-mm field guns, the latter by the French 75-mm gun and 155-mm howitzer. Their purpose, of course, is to return the gun “into battery” after it has recoiled on the carriage.

The recoil mechanism is a study in itself, of which there are two schools—the advocates of the spring and of the air recuperators. Great Britain, Germany and the United States have been the advocates of spring recuperation and France of air recuperation. Great Britain and the United States were of the spring school, undoubtedly, because of the lack of a satisfactory air recuperating system; which is rather strikingly proven by the fact that both countries have adopted air recuperation since they have procured or developed satisfactory types.

Both schools have grounds for their position, however. The spring school has in its favor simplicity of design and manufacture and ease of replacement, which can be done in the field. On the other hand, spring recoils have many breakages and greater weight combined with a high replacement of weakened springs, the life varying from 3000 to 8000 rounds.

The air school has in its favor a high order of efficiency—smoother action, general all around efficiency and less weight. But the air recuperator is difficult to manufacture, costly, and when damaged must go to the rear to be repaired; which, however, it seldom needs.

In mounting the spring recuperator, the most recent practice has separated the recoil mechanism from the springs in order to distribute the piston rod pull, thus preventing whip and allowing easy access to the various parts for replacement, refilling and repairs. In order to lower the center of gravity, the gun is slung under the recoil cylinder with the two spring recuperators below and on either side.

Air recuperators are invariably located below the gun for protection and because of their large size and shape, which adapt them for attaching the elevating mechanism.

BATTERY OR FIRING POSITION

IN-BATTERY OR FIRING POSITION

HYDRO-SPRING RECOIL SYSTEM

HYDRO-PNEUMATIC RECOIL SYSTEM WITH FLUID IN DIRECT CONTACT WITH THE AIR

In either system, the recoil is taken up by means of oil or glycerine and water passing through an orifice created by a slotted piston passing over ribs of varying height, or through a valve on the pressure side of the piston, or by a solid or perforated piston passing through a perforated intermediate cylinder.

The latter type is particularly adapted to variable recoil guns as the intermediate cylinder can be rotated, thus throwing varying orifices into position for the flow of oil.

Counter recoil is accomplished by the springs or by the air pressure in the hydro-pneumatic system, in which the air pressure is sufficient to hold the gun in battery at all elevations and is built up at recoil.

In all counter recoil systems, it is necessary to insert a buffer to take up the remaining energy of the springs or air pressure so as to bring the gun into battery without appreciable jar. Numerous types have been developed and perfected.

The counter recoil brake or buffer in our 3”-gun is a slightly tapered bronze rod, tightly fitting in the cylindrical bore of the piston rod. The retardation caused by forcing the oil in the piston rod out through the small clearance between the buffer and bore of the piston rod eases the return to battery without jar to the gun, which has been forced back by the counter recoil springs.

The physical law that action and reaction are equal has a peculiar emphasis when applied to the firing of a piece of high powered artillery. The force exerted to throw a heavy projectile 7 miles or more from the muzzle of the gun is toward the breech of the weapon in its recoil. How some of these forces are handled safely and easily by mechanical means are almost beyond the mind’s grasp. Not long ago a touring car, weighing two tons, traveled at the rate of 210 miles an hour along a Florida beach. Conceive of such a car going 337 miles an hour—which is much faster than any man ever traveled; then conceive of a mechanism which would stop this car, going nearly six miles a minute, stop it in 45 inches of space and one-half a second of time without the slightest damage to the car. This is precisely the equivalent of the feat performed by the recuperator of a heavy howitzer after a shot.

SHIELDS.

Although cover for the cannoneers had been used off and on since the invention of guns, it had fallen into disuse until it was firmly established as an essential feature by the French on their 75-mm in 1897. All modern field guns have such protection both for the cannoneers and for the delicate parts of the material which would be damaged by shrapnel balls or shell fragments. The shield is made of hardened steel capable of withstanding the impact of a bullet of a service rifle at a 100 yds. range at a standard velocity. For convenience the shield is divided into three parts known as the top shield, main shield and apron, with suitable ports equipped with shutters for the line of vision from sights. The main is fastened to the axle and is rigid. The apron is hinged to the main shield or the axle-swinging forward for the traveling position. The top shield is fastened to the main shield by hinges and swings forward and downward for traveling position.

SIGHTS.

The sights serve three important functions. They improve the vision of the gunner and lay the gun in elevation and direction. The simplest sight is the one over the line of metal which lays for direction only, the second is the tangent sight mounted on a range arc centered on the axis of rotation in elevation usually having a deflection scale to correct for drift and to lead the moving target. This unit lays for range and direction. The last sight is the telescopic or panoramic sight which is mounted on a range arc and lays for direction only, it is the unit for indirect fire, laying for direction, and markedly improving the vision of the gunner. The latest model of the American panoramic sight is superior to any in existence.

For precision in indirect fire, practically all carriages are equipped with some form of range quadrant, containing a means of setting off the angle of site and the range angle. All instruments are equipped to compensate for difference in wheel level. The British carriage automatically corrects for deviation, simplifying the firing date by that element.

WHEELS.

The height of the wheels affects the draft, weight, clearance, and stability of the carriage both as to road stability—i. e., low center of gravity; and firing stability—i. e., the overturning movement about the end of the trail. It is now believed that entirely too much stress has been laid on road clearance. Reducing the height of wheel reduces the weight and road clearance, lowers the center of gravity and increases the firing stability; but it also reduces the angle of gun elevation unless the trail is shortened. Firing stability in general is increased by adding to the weight of the gun, lengthening the recoil, slinging the gun as low as possible and lengthening the trail. The less the height of the wheel exceeds four feet the better, despite the poor draft feature, which is compensated for to some extent by a reduction in weight and turning radius.

AXLES.

Axles are straight or of the offset type. The straight axle is stronger for its weight. The drop axle allows the center of gravity to be lowered.

TRAILS.

Most modern trails are of the sectional built-up type. Some, however, are of tubular and telescopic. The most variable portion of the trail is the spade. It consists of two parts, the spade proper and the float. The former prevents recoil, the latter the burying of the trail. The spades proper are of three types: the fixed, as in the French 75-mm; semi-fixed, as in the 155-mm howitzer; and driven, as in the Deport and American 1916 75-mm. Each has advantages and disadvantages. The driven spade is considered essential for the split trail carriage, as the latter has no means of seating itself; and should one spade take, and not the other the carriage might be damaged when the gun is fired at an extreme traverse.

Split trails introduced a novelty in field gun carriages, in that a compensating device became necessary to adjust for the difference in ground level of the two spades.

CONCLUSION.

Guns are designed to function in a certain way. They are not temperamental. They follow absolutely and certainly fixed mechanical laws. If they fail there is a reason and it can be remedied. Certain parts are given certain shapes and forms, are machined to nice adjustments, and in taking down and assembling them, brains and dexterity are the tools to use rather than force and sledge-hammers. Learn from your text when and how to apply force and above all when not to use it. Treat these guns as you would a friend on whom you know you can depend. They will not fail you.

CHAPTER IV
MODERN ARMAMENT.

THE ARTILLERY OF A FIELD ARMY; ITS FUNCTIONS.

The artillery assigned to a field army should be of such mobility, power, variety and number as to insure the success of its purpose and to enable this success to be gained with the minimum of casualties. The latter point must receive careful consideration in studies of organization, for without adequate artillery preparation and support the successes of the most gallant infantry can in a series of actions become little more than pyrrhic victories. Many actions of our divisions in France resulted in casualties whose numbers decreased in proportion to the number of guns with which divisions were supported. The proportion of guns to the thousand gross strength of infantry, cavalry, and machine guns adopted by the armies of the first class powers before the opening of the present European War in 1914 was:

British, 6.8; French, 4.6; German, 6.4; American 3.2 (Greble Board).

During the war this proportion was constantly increased until at the close under conditions of position or entrenched warfare it was between 8 and 12 per thousand; this varied of course with the activity in different sectors. In quiet sectors and under conditions of maneuver, or open warfare, which necessitated leaving much artillery behind, it was about 6 per thousand.

A program of types of artillery weapons should be founded on the object and the means—that is, the destruction of the target and the projectile to accomplish this. In the study of an artillery program there are two methods of approaching the subject. First, by starting with a minimum weight of projectile and working up to a reasonable maximum, according to some law and taking the corresponding calibers, a theoretical series of guns and howitzers can be expressed. For instance, if the law be doubling the weight of the projectile the series of types could be:

The second and more logical method, and one followed in our service, is to consider the artillery missions and determine the types best suited irrespective of any theoretical series of weights and calibers. However, in the discussion of artillery missions and the proper types for their fulfillment there is a remarkable degree of unanimity of thought on these subjects; and the above table actually contains, with slight variations, the types that are most strongly recommended. While granting the great variety of artillery missions that often shade into each other, it is believed that they can best be considered in three great classes that follow the tactical composition of a field army: those of division, corps and army artillery.

DIVISION ARTILLERY.

Missions. The division artillery, first of all, must have the mobility that will permit it to accompany the infantry of a division and the maximum power consistent with that mobility; its object must be primarily the infantry of the opposing division. It is therefore bound to its own infantry with the closest bonds and its tactical use cannot be separated from that of the infantry. The division artillery must fire, accurately, a man killing projectile and be prepared for quick changes of targets; it must have a great range because of depth, both of its own and the enemy division; it must continually harass the enemy, prevent his movement and force him into cover or protected trenches. On the defensive it must break up the opposing infantry formations by preparing a counter-offensive fire and by annihilating fire on points from which the enemy attacks emerge; and, failing in these, be prepared to use the barrage and shrapnel fire at close range. In the offensive the division artillery must play its part in the complex schemes of artillery preparation by cutting wire, destroying machine gun nests, gassing areas, concentrating on infantry positions and taking the principal part in the deep barrage that should precede the infantry attack. Its fire, accompanying the infantry movement, requires its own movement and by its mobility it often becomes for some time the sole artillery protection in the preparation and holding of a position which has been taken.

Light Gun and Howitzer. The consensus of opinion of artillery officers is that the division artillery missions are best fulfilled by a light field gun and a light field howitzer having a range of at least 11,000 yards. While differing in mechanical features, the field guns of the different European countries are practically of the same type and, though constant effort is being made to improve details, they can be stated as generally satisfactory to their own governments and not liable to any radical changes. The general type of field gun, while capable of fulfilling most of the division artillery missions, must be supplemented by a proper howitzer. There are many instances where the terrain or the lay of the land offers such protection to the infantry that the field gun cannot bring an effective fire. The howitzer has the great advantage that with the proper set of propelling charges and, therefore, choice of trajectories for the same range, protected positions can be chosen for howitzers that guns could not use, and angles of fall obtained on objectives that the normal ammunition of guns would not give. The low muzzle velocity of howitzers admits of their almost continuous use in harassing fire and allows the use of a projectile double the weight of that of a field gun. Such a howitzer renders excellent service in wire cutting and is a useful projector of gas shells. To insure the mobility required of all divisional artillery the weight of the howitzer and carriage should not exceed that of the field gun, or about 4,500 pounds.

Light Gun Discussion. The consensus of opinion of all artillery officers—French, English and American—is that the 75-mm gun, or approximately this caliber, firing a 15-pound projectile or a projectile of approximately this weight, and having a range of not less than 11,000 yards, is a satisfactory weapon at the present time for use with the division artillery. The projectile in question, whether a shrapnel or a high explosive shell, satisfies adequately the criterion of man-killing. At the close of the war the nations were not entirely in accord with respect to their conception of an up-to-date carriage for a light field gun. All the nations whose tendencies have been considered in this report have experienced to a varying degree with field gun carriages, particularly in a desire to design a carriage permitting a greater angle of elevation and greater movement of the gun in the traverse. The Italians have expressed themselves in the modified Deport Carriage; this vehicle is of the split trail type and permits an elevation in excess of 75 degrees, and a traverse on each side of the center of the carriage of about 20 degrees—about 356 mils. Up to the time that the board left France it was not possible to learn the French decision in the matter of a split trail carriage for their light field gun. It is known, however, that several types of this carriage have been designed and tested; it is known, also, that considerable favor has been found with the American 1916, which type has been tested under the auspices of the French Government. In England, however, the board was not able to develop any enthusiasm for the split trail type, although the matter had been seriously considered. In that country the up-to-date field gun carriage appears to be adequately expressed in their new 18-pounder. The vehicle upon which this gun is mounted permits an elevation of 37 degrees and an axle traverse of 4½ degrees on each side. The trail is a box trail and the carriage is simple and steady in its construction and lends itself to rapid production.

Motorization. At some time in the future it is probable that all the division artillery will be motorized. The result of such a change in the prime mover would be to remove the present restriction as to weight of gun and carriage. The board senses a demand in the near future for a light field gun having a maximum range of approximately 15,000 yards; such a range may be achieved by increasing the muzzle velocity and, perhaps, the weight of the projectile, although change in the form of projectiles will give some improvement over the present ranges. It is probable that the limiting features in the design of field guns of the future will be the requirement that it should pass safely over temporary pontoon bridges and that the weight and form and size of ammunition must be such that the present rate of fire will not be slowed down. The board is of the opinion that, except as to perfection of details, the limit of carriage design, as expressed by the most modern type of box-trail and split-trail carriages, has been reached; and feels that with the advent of motor transportation the tendency will be toward a gun mounted on a self propelling carriage and expressing the desires of the field artillery with respect to maximum horizontal and vertical arcs of fire.

Light Gun. Ideal. A gun of about 3” caliber on a carriage permitting a vertical arc of fire of from 5 degrees depression to 80 degrees elevation and a horizontal arc of fire of 360 degrees; a projectile weighing not over 20 pounds, shrapnel and high explosive shell of satisfactory man-killing characteristics with maximum range of 15,000 yards; fixed ammunition, smokeless, flashless propelling charge; time fuse for shrapnel. With shell having safe fuses with different lengths of delayed action after they land. The high explosive shell should be of one type only. Two propelling charges should be furnished, a normal charge for about 11,000 yards range and a super charge for maximum range. The proportion should be 90% of the former and 10% of the latter. A maximum rate of fire of 20 rounds per minute is deemed sufficient.

Light Gun. Practical. For the present, arm brigades with 75-mm materiel. Models 1916, 50%, and 1897 (French), 50%.

Transport. Ideal. Mechanical transport is the prime mover of the future. The introduction of mechanical transport will undoubtedly cause far-reaching changes in the types of gun carriages. It is not possible now to state just how far this will go or whether a gun mounted on a self propelled vehicle or one mounted on some type of trailing vehicle will be the final result. Both types may be necessary. It is urgent that study and development be carried along these lines, as we are on the verge of changes fully as radical as the introduction of the long recoil field gun and carriage, and the country first utilizing the new capabilities opened up by mechanical traction and the caterpillar will have a great advantage in the next war. A limit of 4,500 pounds behind the team has heretofore been imposed on the artillery of this class. The corresponding limit in the future will probably be that imposed by pontoon bridges.

Transport. Practical. Therefore it is thought that four regiments of 75-mm guns (two regiments of French Model 1897, and two regiments of U. S. Model 1916) should be immediately equipped with motors, the remainder to be horsed; mechanical transport to gradually replace horse only after the tractor demonstrates its superiority in service.

Light Howitzer Discussion. The consensus of opinion of American army officers consulted is that a howitzer about 4” in caliber, firing a projectile weighing from 25 to 30 pounds at a maximum range greater than 10,000 yards, is required. This opinion is concurred in by the French, Italians and English, and it appears to be definitely established that the mobility of the light field howitzer should be practically the same as that of the light field gun. The British army was equipped with a 4½” howitzer, firing a projectile weighing 35 pounds and with a maximum range of 7,700 yards; the weight of the howitzer limbered is 4676 pounds—150 pounds more than the weight of the 18-pounder field gun. No evidence was found that the British Government intended making any alterations in the design of this howitzer; naturally they will attempt to increase the range, power and accuracy of the projectile by change in its weight, its capacity and its form. The French artillery was not equipped with the light field howitzer of approximately the same weight as the 75-mm field gun. During the war it was found impracticable to construct a lighter howitzer without interfering with the production of other calibers which were considered more important. In the earlier stages of the war the Italian artillery was not equipped with a light field howitzer; however, before the end of 1917 orders were placed for several hundred howitzers of the 105-mm type. It should be noted that several hundred howitzers of this caliber were being constructed before the armistice and that many have been captured from the Austrians by the Italians; this, so far as the Italians were concerned, makes it certain that a light field howitzer will be furnished by the Italian army. The German and Austrian armies were equipped with a howitzer of the light field type; this weapon had a caliber of 105-mm type.

It fired a projectile weighing 34.54 pounds at a maximum range of 10,500 yards. (Streamline shell.) The weight of the howitzer limbered was 4,500 pounds. In the opinion of the board, the Germans have proceeded on sound principles in their development of the light field howitzer. Their ’98 model was a companion piece to their ’96 field gun and in the years that passed from 1898 to 1916, which included their early war experience, they kept to the idea of the relation of the two pieces even to the extent of including in a field artillery regiment one battalion of light howitzers. Their 1916 models of both light gun and howitzers show the endeavor to keep the pieces in the same class; that is, the weight of the gun and howitzer in action nearly the same, 2,750 pounds and 2,700 pounds; the weight of the gun limbered and the howitzer limbered are the same, 4,500 pounds; the elevation of both the same—minus 10 to plus 40 degrees; the carriages are of the same type; and the extreme ranges of gun and howitzer are respectively 11,700 and 10,500 yards. From the foregoing it is seen that all the important belligerents except the French and the Americans were equipped with a light field howitzer firing a projectile about twice the weight of the light field gun projectile and having otherwise the same general characteristics. There is no evidence to show that the fire of the French and the American artillery was not fully effective as that of any other artillery; however the testimony of the French and American artillery officers is to the effect:

(a) That the lightest howitzer in use, i. e., the 155-mm, was not sufficiently mobile to be a suitable companion piece for the 75-mm gun.

(b) That many times the fire of the 75-mm gun proved ineffective due to its flat trajectory; a howitzer would have been more effective in the attack of certain targets.

(c) That a large volume of fire is necessary.

(d) That while the 155-mm howitzer is more powerful than the light field howitzer its consumption of ammunition for many purposes is wasteful and extravagant and its volume of fire is insufficient.

(e) That the light howitzer is particularly suited for the destruction of wire entanglements; its better accuracy and more powerful projectile make it more suitable than the field gun for that purpose.

(f) That the 75-mm field gun projectile is not so satisfactory a gas shell as the howitzer projectile which has greater weight.

Light Howitzer. Idea. A weapon of about 105-mm caliber on a carriage permitting a vertical arc of fire from minus 5 degrees to plus 65 degrees, and a horizontal arc of fire of 360 degrees. Efforts should be made to develop a carriage which can be used interchangeably for the division light gun referred to above and this howitzer. The projectile should weigh about 30 to 35 pounds and should include both shell and shrapnel. A maximum range of 12,000 yards will be satisfactory. Semi-fixed ammunition with varying charges should be used, otherwise the ammunition should be similar to that provided for the 75-mm guns.

Light Howitzer. Practical. For the present, the division should be armed with the 155 howitzer, Schnieder, but active development and test should be made on a type as stated under “Ideal” above, and with the ammunition and other accessories to it. Upon the development of the carriage as nearly approximating the ideal as may be practically possible, efforts should be made to secure quantity production in order that it may be incorporated in the division as recommended. In addition, a split trail carriage for this howitzer should be developed.

Transport. The light howitzer should have the same means of transport as the light field gun and the same remarks heretofore made as to the probable future development of the field gun also apply to the howitzer carriage.

CORPS ARTILLERY.

Missions. It will be noted above that the division artillery missions did not include their own protection against the enemy artillery. This counter-battery work is the principal mission of the corps artillery. The corps artillery has also the mission of extensive harassing and interdicting fire along the corps front and to a greater depth than the capabilities of the division artillery; also of destructive fire on strong points as well as on railroad facilities and points of supply. For the accomplishment of these corps artillery missions there are two types of artillery necessary, a gun and a howitzer, each having 16,000 yards range and each weighing with the carriage about 11,000 pounds. There is another class of artillery called anti-aircraft artillery to be considered. This is used first in providing anti-aircraft defense for army zones, for certain areas in rear of armies or along a certain line of anti-aircraft defense.

Medium Gun Discussion. The consensus of opinion of artillery officers—Italian, English and American—is that a medium gun of about 6” caliber is necessary. The medium type gun furnished to the American army was the 4.7 (Model 1906). This gun has a maximum elevation of 15 degrees with a corresponding maximum range of 8,750 yards. The British army was equipped with the 5” gun—the carriage permits a maximum elevation of 21 degrees and 30 minutes, giving a maximum range of 12,500 yards. The French army was equipped with, to a certain extent, the 105-mm and the 140-mm gun. The 105-mm gun a maximum elevation of 37 degrees, with a maximum range of 13,900 yards. The 140-mm gun has a maximum elevation of 30 degrees and, with a high velocity, has a maximum range of 19,500 yards. The French 105-mm gun is a modern weapon (1913). The German artillery was equipped with a 105-mm gun (M-1917) with a maximum elevation of 45 degrees, and a maximum range of 16,000 yards. The German army was also equipped with the 130-mm gun, having a maximum range of 16,500 yards. The Austrian army was similarity equipped. The Italians were equipped with a 105-mm gun essentially of the same characteristics as the French 105-mm M-1913.

Medium Gun. Ideal. A caliber of between 4.7 and 5” on a carriage permitting a vertical arc of fire of from minus 5 degrees to plus 80 degrees; a horizontal arc of fire of 360 degrees. Shrapnel and shell weighing not over 60 pounds, maximum range 18,000 yards; with semi-fixed or separate loading ammunition permissible.

Medium Gun Practical. Corps artillery should be armed with the present type 4.7” gun, Model 1906, except that at least one regiment should be armed with the British type 5”-guns purchased abroad.

Transport. All corps guns should be developed for long, rapid hauls. Similar ammunition vehicles should be developed. The wheels for the gun carriage should be rubber-tired.

Medium Howitzer. In the opinion of the French, Italians, British and the Americans, the 155-mm howitzer (Schnieder) was conspicuously successful in the present war. It should, therefore, be retained as a type. The howitzer and carriage as it stands at present, is a highly satisfactory and efficient piece of armament. For the future it is believed that effort should be made to increase the range by improvements in the form of projectile, and it is believed that the form of howitzer and carriage should be studied with a view of obtaining, through modifications, a maximum range of approximately 16,000 yards.

Many batteries of 155-mm howitzers (Schnieder) were motorized in the American Army in France, and the consensus of opinion is definitely toward the retention of this form of prime mover. It is interesting to note that all the important belligerents have settled upon a howitzer of approximately 6” in caliber, and otherwise essentially of the same ballistic characteristics as the type in question. The projectile of this caliber is the smallest projectile which can be called upon to give adequate mining effect against material targets of semi-permanent nature. The place of this howitzer is, therefore, determined by considerations of its destructive ability. It is a splendid destruction and neutralizing weapon.

Medium Howitzer. Ideal. A caliber of about 155-mm on a carriage permitting a vertical arc of fire of from minus 5 degrees to plus 65 degrees; and a horizontal arc of fire of 360 degrees. The projectile should not weigh over 100 pounds and should be interchangeable with projectiles for other guns of this caliber referred to later on. High explosive shell, only, should be supplied.

Medium Howitzer. Practical. The corps should be armed with the 155-mm (Schnieder) howitzer referred to above. The type of fuses for shell should be super quick and long delay.

ARMY ARTILLERY.

Missions. In addition to the division and corps artillery fulfilling the missions outlined above there must be additional artillery available. There are missions of interdiction, neutralization and destruction which fall beyond the activities or capabilities of the normal corps or medium field types; there must exist a surplus of division or corps types, properly transported, for strategic reinforcements of divisions and corps during such times as the normal allotment to such units is insufficient; there must be artillery of special purpose—mountain artillery, trench and super guns and howitzers. Of the above additional artillery, a type of heavy field gun and a type of heavy field howitzer are considered normally necessary in the armament of a field army; the gun should have a range of approximately 25,000 yards, and the howitzer a range of about 18,000 yards. These weapons are more powerful than the medium field types, add range to the interdiction and harassing and to the neutralization and destruction possible with the corps type. Considering the paragraphs pertaining to divisional artillery and the introduction to corps artillery it will be seen that the normal artillery of a field army can be accomplished by the assignments of two caliber, i. e., two light weapons, two medium weapons and two heavy weapons—a gun and a howitzer in each class—and a satisfactory anti-aircraft gun.

Heavy Field Gun. The consensus of opinion of all artillery officers—British, Italian and American—is that the heavy field gun should be of approximately 6” caliber and that guns of greater caliber than this are necessary in limited number for field operations. The French were constructing 194-mm guns during the latter stages of the war. It is believed that in developing this type of gun the French were actuated almost entirely by the necessity for increased range, since the German 150-mm gun, Model 1916, outranged the G. P. F. by approximately 5,500 yards. The French have recently made considerable progress in securing the necessary increase in range with the G. P. F. All of the principal nations engaged in the war used a heavy field gun of approximately 6” caliber. This type has given such general satisfaction that its continuance is assured. The principal mission of the heavy field gun is harassing and interdiction fire, and for these uses the 6” projectile is sufficiently heavy. The maximum practicable traverse and elevation should be provided by the carriage of the heavy field gun. The G. P. F. carriage has given general satisfaction, but its wide tread and the excessive time required to occupy a position are very objectionable features. It is the consensus of all artillery officers—French, British and American—that the heavy field gun should be of approximately 6” caliber and with a range in excess of 25,000 yards, with not less than 60 degree traverse, weighing not more than 12 tons, limbered, capable of occupying and leaving a position quickly, and with a width of tread which does not prevent two-way traffic on ordinary roads. The Italians differ from this opinion only in that they are satisfied with a maximum range of 18,000 yards.

Heavy Field Gun. Ideal. A caliber of about 155-mm on a carriage permitting a vertical arc of fire from 0 degrees to plus 65 degrees; with a horizontal arc of fire of 360 degrees. The maximum range should be about 25,000 yards.

Heavy Field Gun. Practical. Arm with the present type 155-mm G. P. F. and carry on experiments for type of carriage as outlined for division field gun. The fuses should be super-quick and short delay.

Transport. All artillery of this type should be motorized and tested and experiments for ammunition vehicles to correspond with the types of carriages developed, and should be carried on simultaneously.

Heavy Field Howitzer. No type of heavy field howitzer developed during the war has given general satisfaction. The consensus of all army artillery officers—French, English and American—is that two calibers of howitzers are necessary—one a companion piece for the 6” gun and one of the maximum possible power consistent with the necessary mobility. The lighter of these two howitzers should have the same mobility as the 6” gun, with a caliber of about 8” and a maximum range of not less than 16,000 yards. The heavy field howitzer should be of about 9.5” caliber with a range in excess of 16,000 yards; the carriage should provide for wide traverse and must have sufficient mobility to accompany the army in the field. It will probably be necessary to transport this howitzer in more than one load, and the maximum weight of any load should not exceed 12 tons. The average time necessary for occupying a position should not exceed six hours under actual field conditions.

Heavy Field Howitzer. Ideal. A caliber of about 8” on a carriage permitting a vertical arc of fire of from 0 to plus 65 degrees; and a horizontal arc of fire of 360 degrees. The maximum range should be 18,000 yards.

Heavy Field Howitzer. Practical. Use at present 8” material of British design which is on hand.

Railway Artillery. The war has demonstrated the necessity for long range and powerful guns for distant interdiction and harassing work and for super-heavy howitzers for the destruction of semi-permanent fortifications. Artillery of these types can best be mounted on railway carriages and this type of mount offers no serious disadvantages since these guns will not be used except with large forces which require extensive railroad systems for their supply. This does not apply to guns of the type used to bombard Paris; such guns have no military value and their construction is not justifiable.

ANTI-AIRCRAFT GUNS.

Light Gun. Ideal. Caliber about 3” with initial velocity of at least 2,600 f. s.; semi-automatic breechblock, mounted on carriage, permitting 80 degrees elevation and 360 degrees traverse; projectiles weighing not less than 15 pounds, of one type high explosive shell with maximum ballistic qualities and as large explosive charge as possible; fixed ammunition; smokeless, flashless powder, mechanical fuse. In this type every effort must be made to increase the rate of fire and decrease time of flight; this latter is limited only by considerations of a reasonable accuracy life for the gun.

Light Gun. Practical. Arm units with present 3” anti-aircraft equipment. Continue experiments leading to the development of the ideal.

Transport. Ideal. Caterpillar mount or caterpillar trailer mount drawn by caterpillar tractor, each unit to permit a sustained speed of 12 miles per hour.

CHAPTER V
THE 3-INCH FIELD GUN.

THE GUN.

The Gun is known officially as the 3-inch Field Gun, Model 1905. It is a built-up construction of nickel-steel and consists of a tube with a rifled bore, 3 inches in diameter, upon which are shrunk the jacket, locking hoop and front clip hoop. The jacket reinforces the rear half of the tube. The locking hoop serves to secure the jacket from any longitudinal movement to the rear. On the under side of the gun, extending the entire length of the jacket, locking hoop, and front clip, are formed two recoil guides or clips which fit over and secure the gun to the guide rails of the cradle. When the gun is fired, it slides along the guide rails. The dust guard covers the part of the guide rails between the locking hoop and the front clip. The rifling of the bore is right-hand twist and starts with 0 turns at the breech increasing to 1 turn in 25 calibers at 10 inches from the muzzle, then uniform to the muzzle.

Weights and Dimensions.

3 Inch Field Gun, Models of 1904 & 1905.

Breech Mechanism Assembled.

Nomenclature of parts of Gun:—

• Jacket.
• Locking hoop.
• Tube.
• Bore.
• Rifling.
• Lands.
• Grooves
• Breech recess.
• Front clip.
• Muzzle.
• Dust guard.
• Recoil guides or clips.
• Chamber.
• Recoil lug.
• Line sight (front and rear).
• Handy oilers.

THE BREECH MECHANISM.

The breechblock is of the interrupted-screw type, and is provided with four threaded and four slotted sectors. The front end of the axial recess in the block is closed by a bushing. Four ventholes lead from a cavity in the bushing and permit the escape of gas to the rear in case of a ruptured primer. On the rear face of the breechblock are cut gear teeth, in which the gear teeth of the operating lever bevelgear mesh. The breechblock is concentrically mounted on a hub on the block carrier, in which the firing-lock case is fitted. Its position in the breech of the gun with reference to the axis of the bore is eccentric.

The breechblock is closed or locked by a continuous movement of the operating lever. When the block is swung to the closed position the front face of the block latch comes in contact with the rear face of the breech of the gun, thus forcing the latch out of the notch in the breechblock and back into a recess in the carrier. By continuing the motion of closing the mechanism, the breechblock is then rotated on the hub of the carrier and its threads engage with corresponding ones in the gun. When the breechblock is in the closed position, a lug on the firing-lock case serves to lock the carrier to the breechblock and prevents displacement due to a blowback.

The firing mechanism belongs to that type known as a continuous-pull mechanism; that is, no cocking of the firing-pin is required.

The firing-lock case is eccentrically fitted in the hub of the block carrier, in such a position that the axis of the firing-pin is always in line with the bore of the gun. The vent bushing in the front end of the breech block through which the firing pin passes when in the fired position, is fitted eccentrically with reference to the breechblock. This eccentric arrangement of the breechblock, masks the point of the firing-pin and prevents any possible contact between the pin and the primer in the cartridge case when the block is unlocked. The block will be practically fully locked before any contact between the firing-pin and primer can take place.

Nomenclature of important parts of Breech & Firing Mechanism.

Mod. 1905:—

3 Inch Gun Carriage, Model of 1902.
Plan

THE GUN CARRIAGE.

The gun carriage for the 3-inch gun Model 1905 is of the type known as the long-recoil, in which the gun is permitted a sufficient length of recoil (about 45 inches) upon the carriage to render the latter stationary under firing stresses. The gun is mounted upon a cradle which forms a housing for the recoil controlling parts. The cradle rests upon the rocker and has a small traversing motion of 70 mils on each side of the axis of the carriage. The rocker is journaled upon the axle and its rear end is supported by the elevating mechanism, which is seated in the trail.

The principal parts of the carriage are the wheels, axle, trail and elevating mechanism forming the lower carriage, the cradle and recoil-controlling parts constituting the upper carriage, and the rocker and traversing mechanism intermediate between the two. In addition there are provided shields, ammunition carriers, the road brake, and the axle seats.

The Wheels and the Axle. The wheels are a modified form of the Archibald pattern, 56 inches in diameter, with 3-inch tires. The axle is hollow and forged from a single piece of steel. The wheels are held on by the wheel fastenings.

Trail.—The trail consists of two steel flasks of channel section with the flanges turned inward, tied together by transoms and plates to form the sight and the tool boxes. Attached to the trail are the trail spade, float trail handspike, trail handles and the lunette.

Elevating Gear.—The elevating gear is of double-screw type and consists of an inner and outer elevating screw, an elevating-gear bracket, an elevating bevel gear, two elevating bevel pinions, and two elevating crank shafts. The inner elevating screw is a steel screw, threaded with a right-hand thread. It is attached at its upper end by the elevating pin to the rear end of the rocker. The outer elevating screw is of bronze and is threaded on the exterior with a right-hand thread to take the inner elevating screw. On the exterior are also cut two longitudinal keyways, in which the keys of the bevel gear work.

Traversing Mechanism.—The traversing mechanism consists of a shaft, called the traversing shaft, mounted in bearings in the traversing-gear case, and a traversing nut moving longitudinally on the shaft, but restrained from turning with it by its bearings in the gear case. A cylindrical lug on top of the nut fits in a hole in a bronze traversing link, the right end of which is pivoted by the traversing-link pivot to the traversing lug on the underside of the cradle. This pivot is secured to the cradle-traversing lug by a nut and split pin. The left bearing of the traversing shaft is split for the purpose of assembling and rests between two collars on the shaft. The bearing, with the shaft in place, is slipped into its seat in the gear case, where it is held in position by two pins.

TRAVERSING GEAR, VERTICAL SECTION

Elevating Gear Half Elevation and Half Section

The Cradle Complete.—The cradle supports the gun, guides it in recoil, and forms a housing for the recoil-controlling parts; it consists of a flange steel body with the upper edges flanged outward. The flanges are bronze lined, engage the clips on the gun, forming the guide rails for the gun on recoil. Riveted to the bottom of the cradle are four steel forgings, the pintle, traversing lug, rear clip, and elevating and traversing lock lug. The pintle fits the pintle socket in the rocker and forms a bearing upon which the cradle is traversed. The traversing lug has been heretofore mentioned as affording a point of attachment for the traversing-link pivot. The cradle rear clip, in addition to embracing the rear end of the rocker, has a broad bearing on the latter directly over the point of attachment of the elevating screw.

To relieve the pointing mechanism from all strains in travelling, an elevating and traversing lock is provided, by which the cradle may be securely locked to the trail.

The recoil-controlling parts contained inside the cradle are the cylinder, the piston rod, the counter-recoil buffer, the counter-recoil springs and the spring support.

To the rear end of the cradle is riveted a steel cradle head, rear, through which the cylinder moves in recoil and projects for attachment to the recoil lug on the gun by means of the cylinder end stud and nut. The front end of the cradle is closed by the cradle head, front, and the retaining ring.

Recoil Controlling Mechanism

The cylinder lies inside the cradle and is surrounded by the counter-recoil springs. Its rear end is closed and has a projection on the inside to which is screwed the counter-recoil buffer, a tapered bronze rod which fits with small clearance into a bore at the rear end of the piston-rod. The front end of the cylinder is closed by a bronze oiltight gland, through which the piston-rod slides. The cylinder is filled with a neutral oil called hydroline. The interior of the cylinder is cylindrical. Three longitudinal ribs or throttling bars of uniform width but varying height extend along the interior from the rear end to within 19 inches from the front end. Three notches are cut in the piston head, forming ports for the passage of the liquid from one side of the piston to the other. The height of the throttling bars is calculated so that the resistance which the liquid offers, plus the resistance of the springs, is constant and such that the recoil will be checked at the desired point. During recoil the front end of the cylinder is supported by the spring support.

The piston rod is of steel, and is provided with a bronze piston head, screwed against a shoulder at the rear end. The head has three notches cut in its perimeter, which fit over the throttling-bar projections on the cylinder wall. The rear end of the piston is bored out to take the counter-recoil buffer. In counter recoil the oil in this bore can escape only by a small clearance. In this way the return of the gun into battery is so eased and regulated that very little shock and consequent derangement of the aim of the piece occur. The front end of the piston-rod is attached to the cradle head, front, by means of the piston-rod nut.

The counter-recoil springs (three in number each 36 inches long) are helical, being made from a rectangular steel bar coiled on edge. They are assembled in the cradle, end to end around the cylinder and bear in front against the spring support and in the rear against the cradle head, rear. They are assembled under an initial compression of approximately 750 lbs. which is sufficient to return the gun into battery at the maximum elevation. In place of the single counter-recoil springs a set of three inner and three outer counter-recoil springs is also being issued.

The spring support forms a support for the front end of the cylinder and a bearing for the front end of the spring column. It has guide lugs which fit into and glide along guide rails inside the cradle during recoil. The spring support is held in place by the retaining ring.

Action of the Mechanism.

The action of the recoil mechanism when the gun is fired is as follows:—The gun moves to the rear 45 inches on the cradle, carrying with it the cylinder and compressing the recoil springs. The piston rod being attached to a fixed part of the carriage in front, (the cradle-head) does not move. Therefore, since the cylinder moves to the rear, the oil in it must pass from one side of the piston head to the other. The energy of recoil of the gun is therefore absorbed by the resistance which the oil offers when being forced through small openings between the notches in the piston head and the throttling bars along the inside of the cylinder and also by the resistance of the counter-recoil springs to additional compression. The energy stored up by the springs during this compression, returns the gun and cylinder to the firing or original position. This return movement is eased and regulated by the counter-recoil buffer. The piston rod pull and the spring resistance are transmitted to the carriage, but owing to the latter’s weight and the resistance opposed to the trail spade by its engagement in the ground the carriage remains stationary.

Weights and Dimensions.

Nomenclature of important parts of the Gun Carriage:—

• Axle
• Trail, consisting of—
• Flasks (right and left)
• Tool box
• Elevating gear transom
• Rear sight box
• Spade
• Spade Edge
• Float
• Handspike fulcrum
• Cradle, head, rear
• Gun slides or Guide Rails
• Cradle Pintle
• Traversing lug
• Rear clip
• Lug for elevating and traversing lock
• Bracket seat, firing handle
• Quadrant fastening
• Rear-sight bracket support
• Front-sight bracket support
• Spring-support guides
• Retaining ring, with hasp and fastening
• Cradle head, front
• Shoulder guard
• Cradle brush
• Recoil-indicator throw
• Recoil indicator
• Cylinder head
• Cylinder with cylinder end screwed in
• Cylinder end stud and nut
• Counter-recoil buffer
• Rings, packing
• Gland
• Piston rod, with plug, screwed in
• Piston
• Piston-rod nut
• Filling plug with gasket
• Drain plug
• Spring support
• Counter-recoil springs
• Rocker
• Cradle Pintle socket
• Elevating and traversing lock
• Traversing mechanism, consisting of—
• Traversing-gear case
• Traversing plate
• Handwheel with handle and spindle
• Traversing shaft
• Traversing-shaft bearing in two parts
• Traversing link with bushing
• Traversing-link pivot with nut
• Azimuth pointer and scale
• Elevating mechanism, consisting of—
• Elevating pin
• Inner elevating screw
• Outer elevating screw
• Wheels guards
• Trail handles
• Trail seats
• Trail-seat supports
• Sponge-staff socket
• Name plate
• Handspike
• Lunette
• Cradle, consisting of—
• Cradle body
• Elevating bevel gear
• Elevating bevel pinions
• Elevating crank shafts, with handles
• Elevating screw cover
• Axle seats, include—
• Seat arms
• Seat-arm guards
• Foot rests
• Tie rods
• Shield braces
• Apron shield
• Apron latches
• Main shield, consisting of—
• Main shield
• Hood
• Shutter, open-sight port
• Shutter, panoramic-sight port
• Top shield, consisting of—
• Top shield
• Top shield fastenings
• Road brake, includes—
• Brake beams
• Brake shoes
• Springs with covers
• Brake rods
• Brake lever
• Brake shaft
• Brake segment with two segment racks
• Ammunition carriers
• Range quadrant case
• Panoramic sight case
• Front sight
• Rear sight, consisting of—
• Rear-sight bracket with shank socket
• Rear-sight shank
• Panoramic sight
• Range quadrant
• Wheels, consisting of—
• Felloe, segments
• Spokes
• Tires
• Hub boxes
• Hub liners
• Hub-latch plungers
• Oil Valve
• Carriage bolts and nuts
• Hub bands
• Hub caps
• Wheel fastenings
• Plugs

THE 3-INCH GUN (CAISSON) LIMBER.

The limber is of metal throughout excepting the spokes and felloes of the wheels. The principal parts are the wheels, axle, pintle, frame, ammunition chest, pole, doubletree, singletrees, and neck yoke.

The wheels and wheel fastenings are the same as, and interchangeable with those used on the carriage. Seats for three cannoneers are provided by a perforated metal bucket-holder on top of the chest. The paulin issued to each limber serves as a seat cushion and is held in place by paulin straps. Grip straps are also provided for use by the cannoneers when the carriage is moving at rapid gaits. On the sides and front of, and under the ammunition chest, suitable straps, brackets and connections are provided for securing all tools and accessories. With each limber are issued three tubular oil cans, each in the form of a cartridge and with a capacity of two-thirds of a gallon. These are intended to hold hydroline, lubricating and coal oil and are carried in the central row of cartridge holes in the ammunition chest.

3 INCH GUN CAISSON LIMBER, MODEL OF 1916
SIDE AND REAR VIEWS.

Weights and Dimensions.

Nomenclature of important parts of limber:—

• Pole, complete, consisting of—
• Pole body
• Neck-yoke counter stop
• Neck-yoke stop
• Neck-yoke chafing plate
• Butt reinforce
• Doubletree
• Doubletree rods
• Name plate
• Limber prop
• Foot rest
• Tie-rods
• Pintle with bearing, consisting of—
• Pintle
• Pintle latch
• Pintle latch spring
• Wheels and wheel fastenings
• Axle
• Middle rail
• Side rails
• Ammunition chest, consisting of—
• Hand rail
• Door chains
• Shot bolts
• Bucket holder
• Chest rails
• Chest-rail connections
• Body
• Door
• Cartridge holes
• Diaphragms
• Lantern brackets
• Grip-straps
• Paulin straps
• Various tool brackets
• Various tools
• Paulins
• Picket ropes
• Lanterns
• Canvas buckets

THE CAISSON

The Caisson is made of metal throughout with the exception of the spokes and felloes of the wheels. The principal parts are the wheels, axle, pintle, lunette, apron shield, fuze setter bracket, frame, road brake, and ammunition chest.

Caisson, Plan

The wheels and wheel fastenings are interchangeable with those of the gun carriage and the limber. The caisson road brake is modeled after that of the gun carriage, all parts as far as possible being interchangeable. The frame upon which the ammunition chest rests, is diamond shaped, and consists principally of two steel side rails riveted to lugs on the axle, meeting in front to form the lunette for attachment to the limber, and in rear to form a pintle for attachment of another caisson in case it is desired to tow several caissons by one team and limber, as for instance in the ammunition train. In other respects the construction is similar to that of the limber excepting that the ammunition chest is much larger and has a capacity of 70 rounds. The front of the chest and the chest door are made of armor plate. A bracket for the fuse setter is also provided. An apron shield, similar to the one on the gun carriage is hinged under the axle, giving the cannoneers at the caisson full protection. A spare-pole body can be carried under the caisson frame, large end of pole to the front. On the sides and front of, and under the ammunition chest, suitable straps, brackets and connections are provided for securing all tools and accessories. To lock the caissons and limbers, a padlock is provided. These locks are interchangeable and can be unlocked by the same key. This key is marked “Ammunition.”

Weights and Dimensions.

Nomenclature of important parts of Caisson:—

• Wheels
• Wheel fastenings, complete
• Axle
• Middle-rails
• Side rails
• Pintle with bearing, consisting of—
• Pintle
• Pintle latch
• Pintle-latch spring
• Name plate
• Channel supports
• Frame handles
• Lunette, with nut
• Caisson prop, with chains
• Road brake, consisting of—
• Brake-beams
• Brake shoes
• Brake rods
• Brake-rod springs and covers
• Brake shaft, with two keys
• Brake segment
• Segment rack
• Brake lever
• Spare-pole fastening
• Ammunition chest, consisting of—
• Diaphragms
• Grip-straps
• Paulin-straps
• Chest rails
• Foot rest
• Handrails
• Door props
• Door handles
• Hand rails
• Supports and Brackets for attaching various tools and accessories
• Apron
• Apron latches
• Fuze-setter bracket
• Fuze-setter latch
• Fuze setter
• Paulin
• Picket ropes
• Various tools and accessories
• Spare pole

To Dismount and to Assemble Parts of the Gun and Carriage.

To dismantle and to assemble the breech mechanism.—Grasp the operating lever and open the breech; when the block is open, force the block latch out of its seat in the block by gently pressing it into its seat in the carrier. Take hold of the block and revolve it to the left until it stops; then pull it to the rear, taking care not to drop it. The block latch can now be readily removed. After the firing-lock case has been removed the operating lever can be removed by forcing its pivot up from beneath by a gentle pressure from the palm of the hand. The lever latch can be removed by pressing in on the latch at a point near its lower end opposite its pivot; a hole in the latch is cut eccentric with reference to the pivot and a shoulder on the pivot prevents their displacement until the latch is forced in and the hole is concentric with the pivot. When this occurs, the pivot can be readily pulled out and the latch removed. To remove the block carrier force the hinge pin up by hand until it can be caught by the head, and by swinging the carrier back and forth, if the pin sticks, it can readily be removed, taking care not to drop the extractor lever. The extractor can now be removed from the gun.

To dismantle and to assemble the firing-lock case and mechanism.—Take hold of the milled headed locking bolt situated at the lower end of the firing-lock case, pull it to the rear; at the same time revolve the firing-lock case upward about 45° and pull it gently to the rear. This will remove the case with the firing mechanism complete from the gun. Press the trigger-shaft detent until it disengages from the notch in the firing-lock case. This will allow the trigger shaft with its detent, to be withdrawn. Then gently press on the front end of the firing pin, forcing it back into the casing. This will allow the trigger fork to fall out. Then, with one finger placed on the front end of the sear, force it outward; at the same time grasp the front end of the firing pin, which is roughened for the purpose. Give it a sharp pull. This will remove the firing-pin spring and sleeve from the casing. Then place the front end of the firing pin against a block of wood, bear down on the firing-spring sleeve until the spring is compressed sufficiently to disengage the slot in the rear end of the sleeve from the small lug on the rear end of the firing pin; slightly turn the sleeve, and then the sleeve can be separated from the spring and pin. By an unscrewing motion the spring can be removed from the pin. The sear can be removed by gently pressing it in toward the center of the casing.

To assemble, reverse these operations, taking care before driving too hard on the end of the trigger shaft that the square hole in the trigger fork is in position to receive the tapered end of the trigger shaft. No tools are required for assembling or dismantling this mechanism.

To remove the recoil indicator.—The ends of the clips of the recoil-indicator guide are bent down to form stops to hold the indicator in place. To remove the indicator, these parts are opened up sufficiently to permit sliding the indicator out of the guide. When the indicator is assembled, these clips should always be closed down to prevent its loss.

To dismount the gun.—Elevate the muzzle slightly. Remove the recoil indicator throw, unscrew the cylinder-end stud nut, and shove the gun to the rear until the clips are free from the guides. As the gun slides off the cradle, it must be properly supported. For this purpose, from 6 to 8 men working in pairs with lifting bars are required.

To mount the gun.—Depress the muzzle slightly. Shove the piece from the rear over the cradle guides with the clips engaging the guides. Assemble the cylinder-end stud nut, taking care that the locking stud on the recoil lug enters one of the recesses provided for it in the end of the cylinder. Assemble the recoil indicator throw. The dust guard should be assembled with the gun.

In moving the gun on or off of the cradle particular care must be taken to support the breech end so that the gun clips remain in line with the gun slides. The firing shaft is also quite liable to injury during this operation, and care should be taken to prevent its being struck by the nozzle of the gun or by implements in the hands of the cannoneers. The cradle should be placed at the desired elevation and azimuth before beginning either of these operations and not changed during its progress, since the working of either the elevating or traversing mechanisms when the gun is only part way in battery brings an excessive and unnecessary strain and wear upon those parts.

To dismount the cylinder.—Bring the gun to approximately zero degrees elevation; unscrew the cylinder-end stud nut and the piston-rod nut; remove the cradle head, front. The cylinder is now free and may be pulled out to the front.

To assemble the cylinder in the cradle.—The counter-recoil springs and the retaining ring being in assembled position, shove the cylinder (turned so that the drain plug in cylinder head comes on top) into its seat from the front, with the projecting stud on the recoil lug of the gun entering one of the recesses provided for it in the cylinder end; assemble the cradle head; screw in place the piston-rod nut and cylinder-end stud nut.

Be sure that the projecting stud on the gun enters one of the holes for it in the cylinder end before screwing the cylinder-end stud nut up all the way.

To assemble the parts of cylinder after cleaning.—The parts should be reassembled immediately after cleaning and inspection, and the cylinder filled with hydroline oil issued for that purpose. The piston should be moved back and forth in the cylinder by hand to make sure that all parts are correctly assembled and are without interference. The cylinder should then be assembled in the cradle and the gun pulled from battery by hand and permitted to counter recoil rapidly to insure that all parts are in proper position for firing. This should never be done, however, unless the cylinder is known to be filled with oil. In reassembling the parts the condition of the vulcanized-fibre washers between cylinder head and cylinder, and between cylinder-end stud and cylinder end should be noted; they should be replaced whenever necessary to prevent leakage. In removing and inserting the piston rod care should be taken to keep it central in the cylinder, so as not to bind, burr, or spring any parts. The dismounting and reassembling of the parts of the cylinder should in every case be supervised by a commissioned officer. Before firing an inspection should be made to ascertain that the different parts, especially the piston rod and the cylinder-end stud nuts, are correctly assembled.

To pack the stuffing box.—The stuffing box is packed with five rings of Garlock’s hydraulic waterproof packing, 0.25 inch square. The packing is issued cut into rings of such size that the ends meet around the piston rod. The latter being assembled, each ring, placed so as to break joints with the preceding one, is forced in succession into its seat by a packing tool of copper or hard wood, one end of which is shaped like a carpenter’s gouge and the other end forms a handle strong enough to stand light taps from a hammer. Such a tool may be readily improvised by one of the battery mechanics. After the five rings are firmly seated in the box, screw the gland down on the packing.

In assembling the glands be sure that at least four of its threads are engaged with the threads of the cylinder head; otherwise the threads of the gland may be stripped in firing. With new packing it may be found difficult to insert more than four rings and secure sufficient engagement of the gland. In such a case the box should be packed with four rings and the piece fired a few rounds, after which the fifth ring should be inserted.

Adjustment of the gland.—The adjustment of the gland will require the exercise of some judgment. If screwed up too tight, the frictional resistance of the packing on the piston rod will be increased so much that the counter-recoil springs may fail to return the gun to battery, especially at high angles of elevation. It should be screwed up just tight enough to prevent the leakage of oil through the stuffing box. Ordinarily this can be done by hand, but in cases where hand power is not sufficient the wrench provided for the purpose should be used. When its proper adjustment is determined, the gland should be lashed with copper wire to prevent it from screwing up or unscrewing.

To remove the piston rod.—Unscrew the gland sufficiently to release the pressure of the packing upon the rod; unscrew and remove the cylinder head. The rod may then be withdrawn from the cylinder. In dismounting and assembling the cylinder head (and also the cylinder-end stud), the cylinder should be held from turning by a spanner applied to the head retainer or flange on the front end of the cylinder. It should never he clamped in a vise, as its walls are thin and not intended to withstand such usage.

To remove the counter-recoil buffer.—Remove the cylinder-end stud screw; unscrew and remove the cylinder-end stud; the counter-recoil buffer is attached to the latter.

To dismount the springs.—Bring the gun to approximately zero degrees elevation; unscrew the cylinder-end stud nut and the piston-rod nut; shove the gun about 1 inch from the battery; attach the sleeve end of the spring compressor to the cylinder-end stud and put sufficient strain on the compressor to relieve the retaining ring from spring pressure; then remove retaining ring (and cradle head) by loosening and swinging aside the retaining-ring bolts; ease off slowly on the spring compressor until the springs are free.

To assemble the double counter-recoil springs.—With the cradle at maximum elevation and the trail horizontal, place one outer and one inner spring in the cradle until the front ends are about 2 inches in; set up a separator against the forward end of these sections and enter the second outer and inner springs, keeping the separator upheld between the sections; similarly when the outer end of the second section is 2 inches inside the cradle set up the second separator; place the third outer and inner sections on the recoil cylinder. Screw the spring centering tool onto the cylinder-end stud, the small end pointing rearward; pass the sleeve end of the spring compressor through the gun lug and the inner springs and attach it to the cylinder-end stud. Enter the rear end of the cylinder in the spring at the front end of the cradle and push the cylinder back until the springs are at free height, keeping the spring compressor taut. Attach the block and fall carried in the battery wagon to the spade of the carriage or to some improvised support and connect it to the spring compressor; put sufficient strain on the spring compressor to bring the spring column to its assembled height.

As the spring column approaches its assembled height the spring support must be turned so that its guide lugs properly enter in the spring-support guide grooves in the cradle; assemble the retaining ring, disconnect the spring compressor and the spring centering tool from the cylinder-end stud; push the gun back into battery and assemble the cylinder-end stud nut. When the retaining ring is assembled the nuts for the retaining ring bolts should be screwed up until they just come into contact with the retaining ring. If these nuts are screwed up too tight they will deform the retaining ring, with the result that it becomes difficult to assemble and dismount the cradle head. A wrench is provided for turning the spring support to its proper position.

To assemble the single counter recoil spring.—The same method is followed except that no separators are used. The spring compressor is provided with a second eye at its large end which may be used in case the sleeve end should become broken; in case this end is used, however, it will be necessary to pass the compressor through the cradle from front to rear, through the gun lug. For disconnecting the compressor the method used is identical to that previously described.

The cylinder-end stud nut should never be removed when the gun is at an elevation, and the gun should not be elevated when the cylinder-end stud nut is not in place. To prevent the cylinder-end stud from rotating a screw for the cylinder end is provided. This screw for the cylinder end must be removed before attempting to unscrew the cylinder-end stud.

Since the springs are assembled under an initial load of over 750 pounds, a pull of more than 750 pounds must be exerted upon the spring compressor in assembling them. This can be done by passing a handspike through the loop at the rear end of the compressor and making use of the service of the entire gun squad, or the block and tackle may be used as described above. To avoid the possibility of injury to the gun squad in compressing or releasing the springs, all should be required to keep arms and bodies away from the front of the spring column during these operations.

CHAPTER VI
FRENCH 75

GUN.

Weights and Dimensions.

CARRIAGE.

Weights and Dimensions.

The gun is of the built-up type and consists of a forged steel tube which extends from muzzle to breech. A breech hoop is shrunk over the rear of the tube and extends beyond it to provide a breech recess. This recess is threaded with seven threads to take the breechblock. A bronze jacket encircles the central portion of the tube. Inner and outer locking hoops screw to and firmly fasten the tube, hoop and jacket together and prevent them from separating under the stresses of recoil. A muzzle hoop is screwed on the tube at the end of the muzzle.

75 M.M. FIELD GUN
MODEL OF 1897 (FRENCH)

75 M.M. FIELD GUN
MODEL OF 1897
(FRENCH)

A recoil lug on the under side of the breech hoop forms a point of attachment between gun and recoil mechanism through the media of a piston rod and coupling key.

The rear sight is attached to the rear portion of the breech hoop. On top of the hoop at its rear end are two quadrant seat plugs. The front sight is fixed on top of the rear end of the jacket. A sweeper plate which sweeps and lubricates the roller is secured to the front end of the jacket.

The breechblock is the Nordenfeld rotating type, cylindrical with seven threads which serve to screw it into the rear of the breech. The breech is opened and closed by rotating the block 120 degrees around its axis. The block advances during the rotation due to the pitch of its threads and forces the cartridge case into the bore. The gun cannot be fired until the block has been completely closed, a condition which must exist before the striker of the firing mechanism is in line with the primer cartridge of the projectile.

The extractor consists of three parts:

1. Two arms connected by a hollow shaft.

2. A spindle which passes through the shaft and fastens it to the breech.

3. An extractor tang.

The action of the extractor is as follows: When the breech is closed the arms of the extractor are pressed against the face of the tube by the rim of the cartridge case which bears against them. The extractor tang projects into a groove in the inner face of the breechblock known as the loading groove. This groove is circular and its depth is equal to the projection of the extractor tang. It terminates in a helical guide surface called the “ejecting ramp.”

75 M.M. FIELD GUN
MODEL OF 1897
(FRENCH)

The first part of the movement of opening the breech serves to move the grooves in front of the extractor tang. This pressure forces the extractor tang back into its slot in the breech hoop and as the extractor tang is firmly seated in the extractor, the arms of the latter are rotated around the extractor spindle. The arms being brought to the rear, press against the rim of the cartridge case, which is thereby started and ejected.

Inversely (the breech being open) when a cartridge case is smartly inserted in the chamber the rim carries the arms of the extractor forward. The extractor tang is thereby forced against the beveled surface of the ejecting ramp and automatically starts the closing movement of the breechblock.

A safety catch is provided to keep the breech locked between the time that the breech is closed and the shot is fired.

The firing mechanism consists of a striker or firing pin seated in the breechblock, a firing hammer, firing rack, spring and lanyard. By pulling the lanyard the hammer is drawn back and the rack moves forward against the compression of the spring due to its being geared to the hammer. When the lanyard is released, the spring forces the rack back which in turn causes the hammer to fly forward and strike the primer. A safety device is provided for locking the hammer while the piece is in the traveling position.

THE CARRIAGE.

The gun is mounted upon a cradle which encloses the recoil and counter-recoil mechanisms. The device for elevating the gun through the angle between the horizontal and the line gun-target (angle of site) is interposed between the trail and the rocker while the device for giving the gun elevation for range is placed between the rocker and the cradle. This arrangement is known as the independent angle of site or independent line of sight. It has the advantage over the three-inch type in that it allows the range elevation to be altered without disturbing the elevation for site.

75 MM. GUN CARRIAGE, MODEL OF 1897 MI(FRENCH).
LONGITUDINAL SECTION

75 MM. GUN CARRIAGE
MODEL OF 1897 MI FRENCH
REAR VIEW

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
LEFT SIDE

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
RIGHT SIDE

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
PLAN VIEW

The principal parts of the carriage are: trail, axle, wheels, brakes, shields, angle of site elevating mechanism, range elevating mechanism, traversing mechanism, rocker, cradle and sights.

When traveling or resting, the tube rests on the cradle which supports it by means of the jacket. When firing, it recoils on the cradle by means of the rollers. The jacket has two pairs of rollers, and the muzzle hoop is provided with a single pair of rollers. On the upper part of the cradle are the lower slides, on which the jacket rollers, supporting the tube, roll during the recoil. When the jacket rollers are about to leave the lower slides, the muzzle rollers come under the upper slides; the tube is then supported until the end of the recoil by the muzzle rollers and the more forward of the two pairs of jacket rollers. This device gives the gun a long recoil upon short slides. Inclined planes are used in such a manner that when the gun returns into battery the rollers rise from the lower slides thereby relieving the slides from the weight of the tube when the tube is in the traveling position.

The carriage supports the cradle which in turn supports the tube. The cradle and the tube together are displaced, during the laying for elevation with respect to the carriage which remains stationary. The carriage is held steady on the ground by means of the trail spade which with abatage prevents the carriage from recoiling on the ground.

Abatage consists of elevating the wheels on the brake shoes which are provided with small spades which prevent lateral movement. The brake shoes are fastened to brake beams attached to a sliding rack beneath the trail in such a manner that the abatage frame may be placed under the carriage during travel. In preparing to fire, the frame may be adjusted to allow the brake shoes to slip from a position in rear of the carriage wheels to a point directly beneath the wheels.

75-MM. GUN CARRIAGE, MODEL OF 1897, MI(FRENCH) WHEEL BRAKE MECHANISM

Abatage is accomplished as follows: (1) The brake shoes are dropped to the ground in rear of the point of contact of the wheels with the ground; (2) The trail is lifted, turning around the axle, until the spade is about five feet in the air. Tie rods and a slide working on a rack beneath the trail move forward in this action; (3) The trail is then brought down. The rack prevents the slide from moving to the rear and the carriage turns on the abatage frame until the wheels rest upon the brake shoes. This gives the gun a three point support, two small spades under the wheels and a larger one at the end of the trail.

Laying in direction is accomplished by traversing the piece on the axle. The trail spade is fixed and the axle is straight and rigid so that in the movement of the gun to the right and left on the axle both wheels must turn—one to the front and one to the rear. The device for laying for direction is composed of a threaded axle, which is prevented from rotating by a spur and a sliding nut which is contained in a box fixed on the left flask of the gun. This nut bears one of the bevel gears, which is put in motion by the hand wheel. The traverse is three degrees either side of the center or a total of 6 degrees or about 105 mils.

Laying for elevation. To obtain greater accuracy and speed in firing the 75 has an independent angle of site. A rocker with two trunnions is interposed between the cradle and the carriage. The rocker trunnions are seated in the cradle trunnions and support them. This gives the same rotating axis to both rocker and cradle. This is necessary for the mechanical addition of the angle of site elevation and for the range elevation. When the angle of site handwheel is revolved it turns a pinion, which meshes in the rocker rack and thus causes the rocker to move in relation to the carriage. This gives the cradle through the rocker the elevation equal to the difference in elevation between the target and the gun. It is independent of the angle given to the gun for the elevation due to range to the target.

75 MM. GUN CARRIAGE, MODEL OF 1897 MI(FRENCH).
RANGE ELEVATING MECHANISM

The angle given the gun for range is effected through a telescopic screw. This screw is fastened at one of its extremities in the rocker and at the other in the cradle. The nut which receives the elevating screw is seated in an oscillating support which allows it to always remain perpendicular to the axis of the bore at any elevation.

The angular displacements of the cradle with respect to the rocker (angle of elevation) are recorded by the elevating system composed of a graduated arc and a range drum. The lower part of the arc is connected with the right arm of the rocker. The arc is graduated in meters. When the range handle is turned the arc does not move, but a brass slide block connected with the gun and the cradle and bearing an index slides along the arc. It is thus possible to set the range in meters.

However, the arc graduations are not very legible and it has been supplanted by a graduated range drum having more legible readings.

The black part of the arc bears a rack which meshes with a pinion, which in turn rotates around an axle fixed on the cradle. When the cradle moves, the pinion rotates and carries with it the range drum.

The elevation on level ground varies from a minus 11 degrees to a plus 20 degrees. Greater elevation may be obtained by sinking the spade.

The Recoil and Counter-recoil mechanisms are of the Hydro-pneumatic type. Their accurate description is a secret. The following brief description will give only a general idea of the working of the mechanism. The whole apparatus is inside of the cradle through which are bored two cylinders: an upper cylinder 40 mm diameter, and a lower cylinder 66 mm diameter. These cylinders may communicate through a large hole. A piston moves in the upper cylinder, the piston rod, 24 mm diameter, being fast to the gun.

In the lower cylinder are: (1) The valve carrier pipe screwed in the rear part of the cylinder supporting spring valves; in the inner walls of the pipe are cut two grooves; the valve carrier pipe is ended by a circular ring. (2) The diaphragm with its hollow rod. (3) The loose piston with its small rod, which may come in contact with the upper rack of the gauge. The two cylinders are full of liquid, usually Russian oil. The front part of the upper cylinder in front of the piston may communicate freely with the air through the Front Plug. The front part of the lower cylinder is closed by a plug and contains compressed air at a pressure of 150 kg. per sq. cm.

Operation. In recoil the piston of the upper cylinder compresses the liquid, which has to pass through the spring valves and between the circular ring and the hollow rod of the diaphragm. The passage of the liquid through these different openings constitutes the braking effect. In so moving the liquid opens the valves, which are widely opened at the beginning of the recoil and gradually close in proportion to the decrease of the speed of the recoil. At the same time, the air of the recuperator is compressed by the action of the liquid on the diaphragm.

When the recoil is finished, the compressed air pushes back the diaphragm. The liquid thus compressed acts on the small cylinder piston and obliges it to come back into its initial position, bringing with it the tube.

The liquid in flowing back completely closes the valves and must pass between the diaphragm rod and the inner wall of the pipe. At beginning of the return into battery, the space between the rod and the bottom of the groove is large. This space decreases in proportion to the progress of the return. The passing of the liquid through this constantly decreasing space causes the braking which at the end reduces the speed of the return to nil.

CARE AND PRESERVATION OF FRENCH 75.

Dismountings.

Care of Recoil Mechanism.

(Chief Mechanic Only)

Caution.—Never remove piston rod nut, as piston is under pressure and would pull piston rod into cylinder.

The recoil apparatus proper cannot be dismounted.

If properly taken care of the recoil mechanism will not go wrong for years; but if neglected, its destruction is only a matter of very little firing.

The position of the gauge finger is the index as to whether or not the recoil is being properly absorbed.

The joints are not absolutely tight, the slight leakage which takes place during fire or even when gun is at rest is not important.

In normal firing conditions the recoil apparatus contains a slightly greater quantity of oil than absolutely necessary; this quantity is called the “reserve.” When the reserve is exhausted any loss is liable to reduce the quantity strictly necessary. The loss may prevent the gun from fully returning to battery when firing.

The amount of reserve is indicated by the position of the gauge.

No reserve: The gauge finger is down deep in its recess.

Full reserve: The end of the gauge finger is level with the gauge index.

Excess reserve: The gauge finger projects beyond the index.

No firing should be done with an excess reserve.

The gauge finger should be between the index and ⅛ inch below the index.

It is the duty of the Chief Mechanic to see that the gauge finger is in the proper position before firing.

It is the duty of the Executive and the Chief of Section to see that the gauge finger is in the proper position during fire; if it moves from this position the Chief Mechanic will be called to make the proper adjustments.

When the gauge finger has been brought to the proper position there are only two conditions which call for tampering with recoil apparatus.

1. The gun goes into battery too slowly, or has to be pushed in.

In this case the gauge finger will usually be found too deep in its seat, and the pump will have to be used. If the gauge is in the proper position look at the slides. Either they will be found dirty or bits of the wiper may be nicked off. In the latter case the gun can be fired without the wiper.

2. The gun jumps badly. In this case the gauge finger will generally be found beyond the index. When this is the case the oil extractor must be used until the gauge finger is in the proper position.

If after cleaning slides, putting gun in abatage and adjusting gauge finger, the gun still jumps badly—complete draining of the reserve and refilling will frequently remedy the trouble.

CHAPTER VII.
75-MM. FIELD GUN MODEL 1916.

THE GUN.

Twist, right hand, zero turns from origin to a point 2.89 inches from origin. Increasing from one turn in 119 calibers at a point 2.89 inches from origin to one turn in 25.4 calibers at a point 9.72 inches from muzzle. Uniform from a point 9.72 inches from muzzle to the muzzle.

Description of the 75-MM Field Gun.

The gun is built up of alloy-steel forgings, consisting of a tube, jacket, breech hoop, and clip. All of the parts are assembled with a shrinkage.

The tube extends from the muzzle to the rear end of the powder chamber and two recesses are cut in its rear face to form seats for the lips on the extractors.

The jacket is assembled over the muzzle end of the tube. The jacket carries two flanges on its lower side, which form guides for the gun in the cradle of the carriage, and a lug on top near the forward end which contains a T slot, which holds the recoil cylinder in place. The rear end of the jacket is threaded on the outside to receive the breech hoop.

The breech hoop is threaded at its forward end and screws on to the rear of the jacket. The breech ring carries a recoil lug at the top for the attachment of the hydraulic recoil cylinder, and another lug at the bottom for attachment of the two spring piston rods. The rear part of the breech hoop is cut away to form the breech recess.

The clip is a short hoop shrunk on the tube near the muzzle. It carries two lugs on its under side which form guides for the gun in the carriage.

The rear ends of the guides on the jacket are extended to the face of the recoil lugs by short extensions riveted in place to prevent entrance of dust between surfaces of the guides and their bearing surfaces on the cradle. For the same purpose the forward ends of the guides on the jacket are connected by steel-plate dust guards with the rear ends of the guides on the clip.

Description of the Breech Mechanism.

The mechanism is known as the drop-block type, and is semi-automatic in design in that the block closes automatically when a round of ammunition is inserted. A rectangular hole extending through the rectangular section of the breech hoop forms seat for the sliding block. The upper part of the breech hoop in rear of this slot is cut away, leaving a U-shaped opening which permits the passage of the cartridge case.

75-M.M. FIELD GUN BARREL

75-M.M. FIELD GUN MODEL OF 1916 MIII BREECH MECHANISM.

75-MM. FIELD GUN MODEL OF 1916 M III BREECH MECHANISM

Recesses cut in both the side faces of the breech recess form seats for trunnions for the two extractors. Holes bored into these recesses from the rear face form seats for the extractor plungers, springs and plugs. The block slides up and down in the breech recess under the action of the operating arm which is pivoted on the operating shaft and acts as an oscillating crank in raising and lowering the block. The operating shaft which rotates the operating arm is actuated by the operating handle. The operating handle is provided with a latch to keep it in the closed position and is connected by a chain, piston, and piston rod to the closing spring, which is carried in the closing-spring case. The closing spring is under compression and tends to keep the block closed or to close the block when it is opened.

When the block is opened as far as it will go, it is locked in that position by the inside trunnions on the extractors. These trunnions are forced over horizontal shoulders on the block by means of the extractor plungers and holds the block in the open position. When a cartridge is pushed smartly into the gun, its rim striking against the lips on the extractor frees the trunnions from the shoulders on the block and allows the block to close under the action of the closing spring.

A continuous-pull firing mechanism is carried in the recess bored out in the center of the block and is operated by the trigger shaft which projects from the bottom of the block. This mechanism is cocked and fired by one continuous motion of the trigger shaft so that in case of a misfire the primer may be struck a second blow by releasing the shaft and rotating it again. A lanyard may be attached to the projecting end of the trigger shaft.

CARRIAGE.

Description.

The carriage is of the split trail, variable long-recoil type. The length of recoil is regulated automatically, so that the breech of the gun will not strike the ground on recoil at an angle of elevation of less than 47 degrees. At elevations greater than 47° a hole must be dug for the breech in recoil.

The gun is mounted in slides on a cradle formed by the spring cylinder. The spring cylinder is suspended by trunnions mounted in bearings in the top carriage, which is supported by the pintle bearing to which are attached axle arms bearing in the wheels.

The carriage has an independent angle of site elevating mechanism, by means of which a maximum depression of seven degrees and an angle of elevation of 11 degrees may be obtained. The remaining elevation is obtained through the elevating handwheel.

• The principal parts of the carriage are:
• Trail
• Cradle
• Recoil mechanism
• Top carriage
• Pintle bearing
• Equalizing gear
• Shields
• Angle of site mechanism
• Elevating mechanism
• Traversing mechanism
• Axle seat
• Brake mechanism
• Shoulder guards
• Firing mechanism
• Sight, model of 1916
• Wheels.

75 MM. GUN CARRIAGE MODEL OF 1916.
LEFT ELEVATION.

75 MM GUN CARRIAGE. MODEL OF 1916.
RIGHT ELEVATION.

The trail is made in two halves of box section built of bent and riveted steel plate. Each half is bolted to a lug on the equalizing gear, so that it may be rotated horizontally from the junction point of the trail to the point where the trail hits the wheel.

The trails are locked together in traveling position by means of a cone-shaped vertical lug on the lunette bracket which fits in a socket in the trail coupling, and is locked in place by the trail-coupling latch. Trail-coupling latch has a handle and catch with a vertical spindle seated in a socket in the lunette bracket. A handle-return spring is assembled around the spindle and the latch engages a catch on the trail coupling when trails are fixed in the traveling position. Latch is opened by moving handle forward.

Lunette consists of a ring for attaching the carriage to the limber and is bolted through the lunette bracket.

Floats are attached to the bottoms of both trails at their rear ends, consisting of flanged steel plates for the purpose of increasing bearing area of the trails on soft ground.

Spade bearings are riveted to rear of the trails and form bearings for spades in firing position. Spades are driven through the bearings, and their upward movement relative to the trails is prevented by spade latch.

Spade-latch bracket consists of a bronze plate with a cylindrical chamber for a spring and plunger and two bearings for latch-handle pin. Bracket is riveted to the inside top of trail in front of the spade. Spade-latch plunger, with a spring assembled around it, is seated in the chamber and the spade-latch handle is pinned in the bearing. Top of handle extends through the trail and is roughened for use as a foot pedal. Lower part of handle engages with the plunger. When the spade is driven the plunger is forced into a notch in the spade by means of the spring, and the slope on face of plunger allows a downward movement of the spade and prevents upward movement. To release spade the foot pedal on latch handle is pressed down, disengaging plunger from spade, and the spade is removed.

Trail handles are riveted to outside of both trails for lifting trails. Name plate is riveted to outside lower left trail. It is important that the number of carriage on this plate be recorded by the officer in charge of the unit to which it is assigned and that this number be used as a reference in all correspondence. Wheel guards, rear, are plates riveted to the outside lower left of both trails for the protection of trail bodies against contact with limber wheels on short turns. Trail guards are bent plates riveted to the top of trail in front of trail-coupling latch to prevent battering of trails by sledges used for driving the spades.

Sponge-staff fastenings are riveted to tops of both trails. Sponge staffs are inserted in upper rings of staff fastenings and the lower ends are clamped in place. The smallest section of sponge staffs fits in sponge fastenings.

Sledge fastenings are similar to sponge staff fastenings and are riveted to the outside of each trail. Wheel guards (front) are plates riveted to the outside of trails near the front to prevent contact of trails with wheels when the trails are separated.

Spare parts case is a steel box with a hinged steel cover provided with a bolt snap and padlock riveted to the outside of front left trail. This case contains spare parts for emergency use.

Trail seats are made of formed bent plates riveted to the tops of trails near breech of gun. Oiler support with springs is under the right-hand trail seat. Oiler rests on this support and is held in place by springs.

75-MM. GUN CARRIAGE, MODEL OF 1916.
REAR VIEW.

75 MM. GUN CARRIAGE, MODEL OF 1916.
PLAN VIEW.

Traveling lock bar consists of a forged steel bar pinned to lock bar bearing on left trail and made to swing across trails in traveling position and along left trail in firing position. In traveling position the socket in the middle of the lock bar engages with the traveling lock stud in the bottom of cradle, and right end of lock bar is held in lock bar clip on right trail by the latch. To disengage the latch for firing, the latch handle is lifted and the lock bar swung to fastening in left trail, where it latches.

To lock the cradle, the gun is brought to 0 azimuth and the traveling lock pointer on right trunnion cap brought to line marked “March.” In this position the traveling lock socket fits over stud, and the lock is latched. The latch consists of a lever pinned at one end to the lock bar with a plunger pinned in center extending through the bar with a spring around the plunger body to hold the latch in place.

Trail connections are riveted to front end of trail and bolted to equalizing pinions.

The cradle comprises the spring cylinder with attached parts.

The spring cylinder is below and shorter than the gun. It is in the form of two cylinders joined at the center, with axes in the same horizontal plane. Above the cylinders are the gun ways, parallel to the cylinders, bronze lined, and opening toward the center line of cylinders. Traveling lock stud is bolted through a lug at the rear and below the cylinders. Firing-shaft bracket is riveted to the left side and range-scale bracket to the right side of the cylinder at its rear end. Shoulder guards are pinned in sockets in both firing-shaft and range scale brackets to prevent contact of the gun during recoil, with the cannoneers. Trunnions are riveted and keyed to the cylinder near center. Elevating arc is bolted to lugs on the bottom of cylinder at trunnions. Piston-rod bracket is riveted to projections on the cylinder above the gun slides near the front end. Cylinder cover is pinned to cylinder clips, which are riveted to the front of spring cylinder. (Note: On some carriages the clips are made integral with the cylinder.)

75 MM GUN CARRIAGE, MODEL OF 1916.
LONGITUDINAL AND TRANSVERSE SECTIONS

The recoil mechanism is designed for variable recoil, the length of which is regulated automatically by the elevation of the gun. The following table gives lengths at various elevations: (These lengths are based on theoretical calculations. Actual lengths of recoil between 8’ and 45’ elevation are generally greater.)

The breech of the gun on short recoil will strike the ground at the level with the bottom of the wheels at an elevation of 47 degrees or over.

The recoil mechanism is of the hydraulic spring type, with the recoil cylinder mounted above the gun and the counter-recoil springs in the cradle below the gun. The recoil cylinder is held in place by a slot machined in the gun jacket at the front and rests in the cylindrical opening in the gun lug above the rear of the gun. It is held in place by the cylinder retainer, which screws into the rear cylinder parallel to the center line.

The recoil valve is a cylinder with a collar at the front end and three lands inside and parallel to the bore. Three rows of holes are bored at the lands. The recoil valve fits inside the cylinder, resting on the lands, and is held in place by a collar bearing against the edge of the counterbore in the cylinder at the front, while the rear end of the valve bears against the inside rear end of the cylinder.

The piston is screwed and pinned to the piston rod and is of bronze, slotted to fit lands and grooves in the recoil valve. The piston rod is hollow for almost the entire length. The front end passes through the gland in the cylinder head and piston-rod sleeve. The front of the recoil cylinder is closed by the front cylinder head, which is screwed in place with a gasket. A bronze gland with four rings of ⁵/₁₆ inch Garlock packing prevents leakage around the piston rod.

The counter-recoil buffer consists of a buffer rod screwed into the buffer nut at the rear end of the recoil cylinder, and extending through the buffer bushing into the interior of the piston rod. The buffer head is screwed and pinned into the front end of the buffer rod. The buffer head is of two diameters and connected by a short cone. The rear end is the smaller diameter and is threaded inside to screw over the buffer rod. The coned surface contains slots leading to a hollow chamber in front. The front end of head is faced and provided with a central bearing for valve stem. The bearing is supported by webs to main body of guide. Valve stem has a stop on rear and a valve screwed to front. Valve is faced to seat on front of the bearing, webs and circular face of main body of guide.

The counter-recoil springs are assembled around spring rods in spring cylinder. Spring rods fit in gun lug and are fixed in place by taper keys driven diagonally through lug and rod. The rod is hollow for entire length, except at the rear, where the outside diameter is decreased to permit entrance in gun lug. Collars are screwed and pinned to front ends of rods. Three coils of inner counter-recoil springs are assembled over the spring rod, surrounded by three coils of outer springs. Inner and outer springs are coiled in opposite direction to prevent nesting, and sets of coils are separated by a bronze separator. Rear ends of cylinder are bushed for spring rods.

The operation of recoil mechanism is as follows:

When the gun is fired it moves back in slides on cradle, carrying with it spring rods, buffer rod, recoil cylinder, and recoil valve. The piston, piston rod, and spring cylinder remain stationary, being fixed to carriage.

75 MM GUN CARRIAGE, MODEL OF 1916.
LONGITUDINAL SECTION, RECOIL AND COUNTER RECOIL MECHANISM

The recoil cylinder being full of oil, this oil is forced by the piston through holes in recoil valve in front of piston up into annular space between valve and cylinder and into space behind and vacated by the piston. The hydraulic resistance caused by forcing the oil through the holes in valve absorbs most of the recoil energy of the gun, and the remaining energy is taken up by compression of the counter-recoil springs and friction.

When the gun reaches the end of recoil all of the recoil energy has been absorbed and the counter-recoil springs acting against spring-rod piston force the gun back to battery position. The purpose of the counter-recoil buffer is to overcome the tendency for gun to return to battery too rapidly, at the same time allowing sufficient speed of counter recoil to permit maximum rapidity of fire. Buffer action is necessary, as the strength of springs required to return the gun to battery at high elevations is greater than is required at lower elevations.

The action of counter-recoil buffer is as follows:

As the buffer rod moves backward in piston rod the valve in buffer-rod head is opened by the pressure of oil in back of valve and the vacuum in front, which forces oil into buffer chamber in front of the buffer-rod head. At full recoil the buffer chamber is full of oil and buffer-rod head is inside the rear end of piston rod. When springs force gun back in counter recoil, buffer rod moves forward, compressing oil in chamber and forcing valve closed. This prevents escape of oil through valve and forces oil to throttle between outside surface of buffer-rod head and inside surface of piston rod, offering resistance to spring action and thus easing the gun into battery. The inside bore of piston rod is tapered at front end to increase resistance and obtain desired decrease in counter-recoil velocity.

If guns fails to return to battery after a few rounds of rapid firing, it is probably due to expansion of oil. This may be determined and corrected by loosening filling plug. If oil spurts out, allow it to run until gun is back in battery. It may be necessary to relieve oil two or three times immediately after filling. Gun should never be allowed to remain out of battery more than 1 inch on counter recoil without determining and correcting the cause.

If gun remains out of battery and the relief of oil does not cause it to return, it is due to:

(a) Weak or broken springs; (b) piston-rod gland too tight; (c) dirt or lack of lubrication in gun slides; (d) distortion of gun on gun ways; (e) distortion of piston rod due to improper counter recoil action.

The majority of cases are due to (a), (b) and (c).

(a) Can be determined only by removing springs, and should be undertaken only after all other methods have been tried.

(b) Can be determined by loosening piston-rod gland. If gland is too tight, gun will return to battery when it is loosened. If gland cannot be loosened, piston-rod is probably distorted.

(c) Flood slides with oil, and if possible retract gun and examine gun ways and slide for dirt.

(d) If possible allow gun to cool for 15 or 20 minutes. In case of (a), (c) or (d) gun can generally be pushed back into battery by hand.

(e) If piston rod or interior mechanism is distorted, mechanism must be disassembled and defective parts replaced. If distortion has occurred, it can generally be identified by very rapid counter recoil for round on which gun does not return to battery. This may be caused by foreign matter in oil causing buffer valve to stick, or by lack of sufficient oil. If distortion has occurred, it will be near gland and can generally be felt by running hand along rod from bracket to gland.

75 MM. GUN CARRIAGE MODEL OF 1916
VALVE TURNING GEAR AND RECOIL CYLINDER ASSEMBLED.

In case of any improper functioning of recoil mechanism during recoil or counter recoil, cease firing until cause has been determined and corrected. A piece is out of action when recoil mechanism is not operating properly and will almost certainly be damaged seriously if further firing is attempted.

After dismounting any part of recoil mechanism or filling recoil cylinder, gun is to be retracted and released to allow counter recoil if possible. In performing this test, valve-turning mechanism must be disconnected and valve turned to correspond to an elevation of carriage of 53° before gun is retracted. Gun must not be held out of battery more than 10 seconds before being released.

Variable recoil is obtained by varying the area of effective throttling holes in the recoil valve. An arm on the trunnion cap is connected by means of connecting rod, valve-turning arm, valve-turning gear, and a piston-rod gear, to the piston rod itself. As the gun is elevated the relation of the cylinder to the trunnion changes, causing the piston rod to turn by means of the valve-turning mechanism. Slots in the piston engage lands in the valve, causing the valve to turn with the piston. As the cylinder remains stationary the location of the lands inside of the cylinder change with relation to the three rows of holes in the valve, and these rows of holes are covered to produce variations in the length of recoil. At long recoil all the rows are uncovered; at intermediate recoil one row is uncovered; and at short recoil two rows are uncovered. The setting of the valve in degrees elevation is shown by the scale on the piston-rod sleeve and index mark on the edge of the piston-rod bracket bushing at the top of the piston rod.

The top carriage carries trunnions of the spring cylinders and rests on pintle bearing. The top carriage bears on the circular bronze slides in upper part of pintle bearing and is centered on the bronze pintle collar of the pintle bearing.

The pintle bearing carries the top carriage, the equalizing pinions and the equalizing gear, and is supported by the axle arms, which are shrunk in the arms of the pintle bearing. Axle arms bear in the wheels.

The object of the equalizing gear is to increase the stability of the carriage in firing when the wheels are at different elevations. Equalizing gear is an H-section with bevel tooth sector on each end and bronze-bushed bearing in the center. It bears over the vertical journal below the pintle bearing and is held in place by equalizing-gear support screwed inside the journal. Vertical deflection is prevented by the equalizing-gear bolts which are fixed to the pintle bearing by means of nut and shoulder, pass through slots in equalizing gear, and support gear on bolt heads. Equalizing pinions are bevel pinions sectors, bronze bushed, bearing over the arms of the pintle bearing, and have the lugs for trail connection bolts. Pinions are held in place by locking rings screwed over axle arms and are free to revolve about the pintle bearing arms.

Equalizing pinions mesh with equalizing gear.

When the carriage is laid with wheels at different elevations, it is more unstable than when wheels are level. If fired under this condition, the force of recoil tends to overturn the carriage. The function of the equalizing gear is to overcome this tendency. When carriage is fired, firing stresses are transmitted to trails, and the side on which the smaller stress is exerted tends to rise. This motion is transmitted through equalizing pinion and equalizing gear to equalizing pinion on other side, applying downward force on this trail and preserving the stability of carriage.

The angle of site mechanism is designed to give the gun a maximum depression of about 6° and a maximum elevation of 11°, independent of the elevating mechanism. The mechanism is operated by two handwheels, one on each side of gun.

75 MM GUN CARRIAGE MODEL OF 1916.
DIAGRAM OF ANGLE OF SITE MECHANISM.

Handwheel on right side operates through bevel gear on handwheel shaft and intermediate shaft, both mounted in angle of site bracket, right, and cross shaft mounted in bronze bushings in top carriage. Handwheel on left side operates through bevel gears on handwheel shaft, mounted in angle of site bracket, left, and cross shaft mounted in bronze bushings in top carriage. Bevel gears on ends of both cross shafts mesh with bevel gear on angle of site worm, which is mounted in bushings in top carriage and held in place by angle of site-worm caps. This worm meshes with teeth cut in rocker.

Rocker is a U-shaped piece with bearings at the tops of both arms and teeth cut in bottom of U. The bearings bear over and are free to revolve about trunnions on cradle independent of trunnion bearing in top of carriage. Top half of right bearing is formed by rocker arm, right, which extends back and carries angle of site scale, pointer, rack, and level and forms a bearing for elevating handwheel shaft. Rear of rocker arm, right, is braced by rocker arm brace, a diagonal hollow rod attached to rocker arm and rocker. Top half of left bearing is formed by rocker arm, left, a diagonal arm extending upward to the rear to form a support for sight. Movement of the angle of site mechanism is limited in elevation by the rocker stop bolted to the side of the rocker and in depression by a screw in the arc.

The elevating mechanism is designed to allow an elevation of the gun of 42° independent of the angle of site mechanism. The mechanism is operated by one handwheel on the right side of carriage, which is turned in a clockwise direction to elevate gun.

75 MM GUN CARRIAGE, MODEL OF 1916.
ELEVATING MECHANISM.

The elevating mechanism is operated through bevel gears on elevating handwheel shaft mounted on a rocker arm, right, elevating intermediate shaft inside rocker-arm brace, elevating cross shaft, mounted in an elevating cross-shaft bearing bolted to the rocker, and the elevating worm, which bears inside lower part of the rocker. The elevating worm meshes with the elevating arc, which is bolted to the bottom of the spring cylinder.

In indirect fire the angle of site in mils is laid off on the angle of site scale with the pointer and the desired range of graduation brought opposite the pointer by means of the elevating handwheel.

Operation of the Angle of Site and Elevating Mechanism. The angle of site mechanism is operated by turning handwheel, the movement of which is transmitted through the shafts and gears to the angle of site worm meshing with the rocker. Movement of the rocker is transmitted directly through the elevating worm, elevating arc, and spring cylinder to the gun, and through the rocker arms to the elevating mechanism, gun, cradle, and sights. The elevating mechanism moves only gun and cradle through movement of handwheel shafts, and the elevating worm inside the rocker, which meshes with the elevating arc.

The angle of site scale is graduated in mils from 170 to 500. The range scale is graduated in meters. The zero setting of the gun is with O on the range scale opposite 300 on the angle of site scale and the level bubble on the rocker arm, right, at the center of the tube. This allows the maximum depression of 7 degrees (about 130 mils) or the maximum elevation of 11° of angle of site mechanism to be read on the angle of site scale against the zero of the range scale.

The sight, model of 1916, which acts as a support for the panoramic or peep sight, is attached to the rocker arm, left.

75 MM. GUN CARRIAGE, MODEL OF 1916.
TRAVERSING MECHANISM.

In direct fire, the axle of the bore is brought on the line of site by operating the angle of site handwheel until the cross hairs of the sight are on the target and the range is laid off independently by bringing the desired range graduation opposite 300 on the angle of site scale. Line of site may be set independent of the range, as there are two angle of site handwheels.

Traversing Mechanism. The total traverse of the gun on the carriage is 800 mils. The traversing handwheel is located on the left side of the carriage and turns in a clockwise direction for left traverse.

The traversing handwheel shaft is mounted in the angle of site bracket, left, and the angle of site bracket cover, left. A bevel pinion on upper end of the shaft meshes with bevel gear on traversing shaft, which bears in angle of site bracket, cover, left and intermediate shaft bearing bolted to top carriage. A bevel pinion at lower end of the intermediate shaft meshes with bevel gear on end of traversing-worm shaft, which is mounted in bearing in top carriage. Traversing worm meshes with traversing rack which is screwed to pintle bearing. Traversing stops are filister head screws between end teeth of traversing racks to limit movement of worm in rack.

The movement of handwheel is transmitted through shafts and bevel gears to worm and rack. Rack is mounted in pintle bearing, which remains stationary, and top carriage moves about its bearing in center of pintle bearing and bronze-lined slides around the outside of pintle bearing. Traversing scale is screwed to pintle bearing above rack, and pointer is formed on traversing worm-shaft bearing.

DISMOUNTING AND ASSEMBLING CARRIAGE.

Note.—The first and most important precaution to be observed in assembling guns and carriages is that all parts must be clean.

Where dismounting but not assembling operation is described, assembling is approximately the reverse of dismounting.

I. To Remove Recoil Cylinder.

1. Remove valve turning gear cover (take out four ⅜” bolts attaching it to the piston rod bracket).

2. Remove valve turning gear, valve turning arm and connecting-rod as a unit by removing split pin, nut, and connecting rod pin from trunnion cap, right.

3. Remove piston rod (remove lash wire and two ³/₁₆” split pins) slide piston rod gear forward and remove.

4. Remove ¼” locking screw from top of piston rod bracket.

5. Remove ³/₁₆” cylinder retainer screw and loosen cylinder retainer, but do not remove retainer.

6. Remove brass spring-rod plugs from rear ends of both spring rods.

7. Screw spring compressor eye into rear of left spring rod. Make loop in compressor and attach double sheave close to cradle. Attach single sheave to lunette by means of loose cord of sheave rope.

8. Man pulling rope with from four to six men, retract gun not less than 10”, and secure rope to lunette.

9. Remove cylinder retainer, slide cylinder forward until free of groove in gun and remove cylinder. Handle carefully.

10. Allow gun to return to battery slowly by slacking off on pull rope.

II. To Disassemble Recoil Cylinder.

Note.—The interior parts of recoil cylinder are made with great accuracy to insure proper operation and must be handled with care to avoid injury.

1. Remove recoil cylinder from carriage. (See I.)

2. Drain recoil cylinder by resting on blocks at front and rear, removing both filling plugs and drain plug, and tipping rear end up to allow all oil to flow out of drain-plug hole.

3. Unscrew buffer-rod nut from rear cylinder head, draw out buffer rod until wrench can be applied on flats, and remove nut. Push rod back into cylinder.

4. Remove lower split pin from gland lock, swing gland lock back until free of notches in gland, and loosen gland with gland wrench. Unscrew front cylinder head with special wrench. Threads may be started by striking handle of wrench with soft hammer. Do not hold cylinder in a vise.

5. Draw out piston rod slowly, supporting it at both ends as it leaves cylinder. Hold recoil valve in cylinder with ends of fingers. Keep receptacle under front of cylinder to catch surplus oil.

6. Drain surplus oil from piston rod by holding vertically over receptacle with piston down and holding buffer rod in place.

7. Rest piston rod on blocks, remove buffer-bushing locking screw, and unscrew buffer bushing, holding piston rod by wrench on flats at front end of rod. Have supporting blocks under both ends of rod so that rod will not be strained.

8. Draw out buffer rod carefully.

9. Draw out recoil valve with fingers. Remaining parts can now be easily disassembled. Buffer head is locked in place with bronze pin, which must be driven out before head can be unscrewed.

III. To Assemble Recoil Cylinder.

This operation is the reverse of II. Be sure that all gaskets and locking screws and pins are replaced and are in good condition. Be sure that all parts of mechanism are perfectly clean and dry, and that oil is clean. Oil must be strained through double thickness of clean cloth and if clean oil is not available use new oil. Do not make piston-rod gland too tight. Tighten with hand and screw up with wrench one additional notch to lock gland. Fill recoil cylinder before replacing on carriage, as follows:

(a) With drain plug in place and filling plugs out, pour hydroline oil into filling hole slowly to avoid the formation of air bubbles.

(b) When oil is level in filling-plug openings, tilt cylinder slightly to allow escape of air and replenish oil.

(c) Loosen filling plug in front end of piston rod enough to allow oil to drip, and tighten plug.

(d) Replace rear filling plug, raise front of cylinder about 6 inches, and tap cylinder lightly with wood block or lead hammer to remove air. Level cylinder, fill, and replace front filling plug. Be sure that all gaskets are in place and properly centered.

Note.—After recoil mechanism has been disassembled and replaced on carriage gun should be retracted 46 inches and eased back into battery slowly to be sure that it is properly reassembled.

IV. To Dismount Gun.

1. Remove recoil cylinder (see I) and breechblock (see VI).

2. Raise and block up trails in horizontal position, elevate gun until axis of bore is parallel with trails, and attach retracting mechanism (see I-7) to left spring rod, retract gun about 6 inches, remove 3-16-inch split pin in left spring-rod key, and drive out key with bronze drift. Ease gun into battery slowly and permit further forward movement of spring rod until rope is slack and front end of spring-rod rests against spring cylinder cover.

3. Transfer retracting apparatus to right spring-rod, retract gun about ¼ inch, remove split pin and spring-rod key, ease gun into battery until spring-rod rests against spring-cylinder cover, and detach retracting mechanism.

Note.—In this position full pressure of springs is against cylinder cover and gun is free to slide in ways. Men should be kept from in front of spring-cylinder and care must be exercised to prevent tipping of cradle to the rear, which may cause gun to slide off.

4. Bring gun to maximum depression.

5. Lower trails to ground, spread trails against wheels, set brake, and bring gun to zero elevation.

6. Requires seven men and four pick handles or implements of almost the same length and strength. Slide gun about 36 inches to the rear by hand, place one pick handle in bore of gun at breech with one man, one pick handle with a man on each side under gun slides at front of cradle, and four men with two pick handles under gun as gun is drawn out.

7. Push gun out of ways, supported by men, and remove.

Note.—In using pick handles do not place them under dust guards at gun lugs. Care must be taken to keep gun properly supported at same level as cradle guides at all points until free of guides.

In remounting gun on cradle be sure that ways are well oiled and ways and slides thoroughly clean. Mounting gun is the reverse of IV.

V. To Remove Counter-recoil Springs.

1. Close and latch trails. (Open spring-cylinder cover.)

2. Set brake and drive one spade (to secure carriage).

3. Remove breechblock (see VI.)

4. Attach spring-compressor to right spring rod (see I-7).

5. Secure single block of retracting apparatus to fixed point, such as “dead man,” driven spade, or tree. The holding power of this fixed point must be at least equivalent to a driven spade and attaching point of rope should not be higher than center of spring rod.

Note.—Sufficient slack of rope must be allowed to permit spring compressor to travel full length of spring cylinder and be detached from spring rod at front end.

6. Retract gun about 6 inches, remove split pin in spring-rod key and drive out spring-rod key with bronze drift.

7. Release retracting mechanism gradually until spring compressor rope is slack, draw spring rod out of front end of spring cylinder, and detach spring compressor.

8. Attach retracting mechanism to spring rod, right.

9. Retract spring rod about ½ inch, remove split pin, and drive out spring-rod key.

10. Release retracting mechanism gradually until spring compressor rope is slack, draw spring rod out of front end of spring-cylinder and detach spring compressor.

Note.—Assembly of counter-recoil springs is reverse of removal. The following precautions must be observed in assembling:

(a) If tension-spring compressor brings spring rod up solid against spring cylinder bushing in rear of spring cylinder, ease off rope slightly and pry up rod with bronze drift until it will enter the bushing.

(b) Before key slot enters gun lug see that keyways in spring-rods and keyways in gun lugs are in line. If not, turn spring-rod by means of drift until keyways are in line.

VI. To Remove Breechblock.

1. Remove operating-shaft detent, slide operating handle to the right as far as the chain will permit, remove 1-16 inch split pin from studlink pin.

2. Remove chain, piston rod, spring piston, piston-rod nut, and locknut as a unit by drawing out of closing-spring case.

3. Remove closing spring from case.

Note.—For complete instructions regarding disassembly of the breech mechanism see page [19].

4. Remove trigger-shaft detent split pin and trigger-shaft detent by drawing it out of the breechblock to the right.

5. Remove trigger shaft by prying gently straight down with screw driver or similar tool. Keep breechblock supported for all succeeding operations.

6. Remove operating handle by sliding to the right and off operating shaft.

7. Remove operating shaft by sliding to the left.

8. Raise breechblock as far as possible (about 3-8 inch), move bottom part of operating arm to the rear, and remove operating arm.

9. Remove breechblock by sliding down free of breech ring.

10. Remove extractors by sliding toward center line of gun.

VII. To Replace Piston Rod Gland Packing.

(Packing, 4 rings, 5-16-inch square Garlock hydraulic packing.)

(Gun in battery or cylinder removed.)

1. Remove lower split pin from gland lock, swing gland lock up out of notch in gland.

2. Unscrew gland with special wrench and slide forward on rod.

3. Remove packing with bent wire.

4. Insert five rings of new packing, one ring at a time, and push each ring home with packing tool of copper or hardwood to fit into gland recess. Break joints in rings and tap packing tool lightly with hammer to drive each ring of packing home.

5. Screw up gland by hand and not more than three additional notches with wrench so that gland lock will catch and replace split pin.

Note.—For the first few rounds after inserting new packing there will be some leakage at gland and occasional tightening will be necessary. Gland should not be screwed up tight with a wrench, as it can be made sufficiently tight by hand to prevent leakage if properly packed.

VIII. To Remove Wheel.

1. Raise and support carriage under equalizing gear near each end (about 12” each side of center.)

2. Disengage hubcap latch; unscrew and remove hubcap.

3. Disengage wheel fastening plunger and remove wheel fastening.

4. Remove wheel.

IX. To Remove Shields.

A. Top shield.—1. Remove four ⅜” pins, two ⅜” locking pins, and lift off shield.

B. Apron.—1. Remove four ⅜” hinge pins and remove apron.

C. Cradle Shield.—1. Remove two ³/₃₂” split pins, nuts and bolts. On carriages number 625 to number 678 inclusive, remove two cradle shield extensions.

D. Main Shield, left.—1. Remove six ½” bolts from shield bracket outer left. 2. Remove three ⅜” bolts from shield socket, inner left. 3. Lift off shield.

Main Shield, right—1. Remove right wheel (see VII). 2. Remove ½” pin from brake band end, remove adjusting nut and force (by hand) brake band out of position, to clear main shield, right. 3. Remove four ½” bolts from shield bracket, outer right, and two ½” bolts from brake lever bracket. Remove two ²/₁₆” bolts from tool and remove tool carrier. Remove three ⅜” bolts from shield bracket, inner right. 4. Lift out shield.

X. To Remove Spring Cylinder.

1. Remove recoil cylinder (I), gun (IV), counter recoil springs (V), sight (XI) and shields (IX).

2. Remove trunnion caps (right and left) by raking out four split pins, loosening swing bolt nuts, and withdrawing ½” trunnion cap pins.

3. Remove rocker stops (right and left) by taking out four split pins and ⅜” bolts.

4. Unlatch and spread trails.

Note.—Seven men and four pick handles (or similar implements) are required for succeeding operations.

5. Post two men with one pick handle at rear, two men with one pick handle immediately in front of elevating arc, and two men with one pick handle at front end of spring cylinder.

6. Raise cradle slowly, slightly to the rear until rocker clears top carriage. Carry to the rear sufficiently to rest middle pick handle in trunnions and transfer two men with handle to rear of carriage. Continue to the rear sufficiently to rest front pick handle in trunnions, transfer men to rear, and remove spring cylinder.

XI. To Remove Sight.

1. Remove three ⅜” bolts from rocker arm, left.

2. Remove one ⅜” pin from sight lever in left trunnion.

3. Remove sight and sight link.

XII. To Remove Rocker and Rocker Arms.

1. Remove spring cylinder (see X).

2. Remove two ³/₃₂” split pins, with ⅜” nuts and bolts, two ⅜” cap screws with lock washers, four ⅛” screws, driving out four O.247” by O.34” by O.872” keys from rocker arms, right and left.

3. Remove rocker arm, left, by sliding up and out of rocker.

4. Remove cross-shaft bearing cover by taking out three ³/₃₂” split pins and removing three ³/₁₆” nuts.

5. Drive out ⅛” pin from intermediate shaft pinion, remove two ⅛” split pins, two ½” nuts, one ⅛” split pin, and one ½” cap screw from rocker-arm cap and remove rocker-arm cap.

6. Lift out elevating handwheel and handwheel shaft as a unit.

7. Draw intermediate shaft up and out of rocker-arm brace, draw rocker down from trunnions (keeping in line with rocker-arm bearings) and remove. Swing rocker arm, right, up and around trunnions until free of range-scale bracket and remove.

XIII. To Remove Top Carriage.

1. Remove spring cylinder (see X) rocker and rocker arms (see XII).

2. Remove angle of site bracket, left, by removing three split pins and nuts from ⅜” bolts in angle of site bracket cover, left, taking off cover, removing nut and split pin from traversing handwheel shaft, removing handwheel and drawing shaft out to the left.

3. Remove two split pins and ¼” nuts from cross shaft pinion case (left) bolts, extract bolts, and remove case.

4. Remove cross shaft pinion case, right, as in XIII-3.

5. Remove split pins and two nuts from cross shafts, right and left.

6. Remove split pins and nuts from four ½” studs securing angle of site bracket, left, and remove bracket with attached parts as a unit.

7. Remove angle of site bracket, right, as in XII-5.

8. Draw out cross shafts, right and left, and remove cross shaft pinions, right and left.

9. Traverse top carriage to the right (by turning intermediate shaft gear by hand) sufficiently to allow traversing stop, rear to be removed. Extract split pin, remove nut, and take off traversing stop, rear.

10. Traverse top carriage to the left until traversing worm is disengaged from rack, remove split pins and nuts from four studs securing traversing worm shaft bearing to top carriage, and remove bearing and attached parts as a unit.

11. Lift out traversing worm with attached parts as a unit.

12. Turn top carriage to the right 90 degrees from zero azimuth, remove three screws that attach traversing rack to pintle bearing and remove traversing rack.

13. Turn top carriage to the right 90 degrees (180 degrees from zero azimuth), remove four screws that attach dust guard to pintle bearing and remove dust guard.

14. Remove two screws that secure clip to pintle bearing and take off clip.

15. Raise top carriage from pintle bearing.

XIV. To Remove Equalizing Gear and Pinions.

1. Remove top carriage (see XIII), wheels (see VIII), brake mechanism (see XV) and trails (see XVI).

2. Turn pintle bearing bottom side up, remove 29 screws which attach washers and binders and remove equalizing-gear cover.

3. Remove split pins and nuts from both locking ring-clamp bolts, unscrew and remove rings (one right, one left).

4. Slide equalizing pinion off axle arms.

5. Remove split pins from right equalizing-gear bolts, hold nuts tight, unscrew and remove bolt, remove nut and washer, remove left equalizing-gear bolt, nut, and washer in the same manner.

6. Remove locking screw and equalizing-gear support (using special wrench). Lift up and remove equalizing gear.

XV. To Remove Brake Mechanism.

1. Remove wheels (see VIII).

2. Remove brake bands, right and left, by extracting four split pins and removing four brake pins from ends of brake shaft.

3. Remove one split pin from each type “A” pin securing brake lever, foot to brake lever bracket and to sleeve extension. Remove type “A” pins and brake lever.

4. Extract two split pins from brake lever sleeve near center of carriage, draw out and remove brake shaft, left.

5. Remove shield bracket, outer right, brake shaft, right and brake lever sleeve with all permanent parts attached, by removing main shield (see IX, D and E), removing split pin and nut from brakehanger bolt, taking out bolt, and sliding parts off axle arm.

6. Remove shield bracket, outer left, by removing split-pin, nut, and brake hanger bolt and sliding brake hanger with permanent parts attached, off axle arm.

XVI. To Remove Trails.

1. Support carriage at front of pintle bearing.

2. Remove two split pins and nuts from connection bolts, drive out bolts with copper drift, slide trails to the rear and remove.

GENERAL INSTRUCTIONS.

Filling Recoil Cylinder (Cylinder Mounted on Carriage.)

If the recoil cylinder is not completely filled, loss of stability will occur and there is danger of serious damage to material. Before firing, a commissioned officer should always verify the filling of cylinder by removing one filling plug (with gun level) in which case oil should be visible above recoil valve.

To fill recoil cylinder when assembled to carriage, elevate the gun about five degrees, remove both filling plugs and pour Hydroline oil in slowly with funnel until oil appears at rear filling plug hole. Level gun and again fill until oil appears at both filling holes. Shake carriage gently and continue to refill slowly until air ceases to come out of cylinder. Replace rear plug, elevate gun about five degrees, remove valve turn-gear cover, and loosen plug in end of piston rod sufficiently to allow oil to drip out. As soon as oil starts to drip, tighten plug; be sure that gasket is centered. Replace rear filling plug, rock carriage to permit air to escape from filling hole and fill with oil. Replace plug, level gun, and perform same operation with rear filling hole. When air is all out of cylinder, tighten both plugs and elevate to five degrees, allow to stand for about five minutes, then remove front plug and again refill. Loosen drain plug and drain out about ¼-gill of oil into receptacle. Do not allow oil to run down into gun slides.

About four quarts of Hydroline oil is required to fill recoil cylinder. Oil must be clean and free from dirt and should be strained through clean linen or muslin cloth before using.

In emergencies glycerin and water, or any buffer or engine oils may be used in recoil cylinders, but should be replaced by Hydroline as soon as possible. Where the above liquids are used, all interior parts of recoil mechanism must be emptied, disassembled, thoroughly cleaned and dried before refilling.

CHAPTER VIII
75-MM FIELD GUN MODEL 1917 (BRITISH).

DESCRIPTION.

The gun is a combination of a built up and a wire wrapped gun. It consists of a tube, a series of layers of steel wire, jacket and breech ring. The tube extends from the rear end of the chamber to the muzzle. Over the rear portion of the tube are wound 15 layers of O.04 by O.25” steel wire. The jacket is fitted over the wire and the tube, and is secured longitudinally by corresponding shoulders and the breech ring, which is screwed over the jacket at the rear, and secured by a set screw. The breech ring is prepared for the reception of the breech mechanism, and is provided on the upper side with a lug for the attachment of the hydraulic buffer.

75 mm. Field Gun, Model of 1917 (British).

75 mm Field Gun, Model of 1917 (British)
Breech Mechanism Assembled

The breechblock is of the swinging type, interrupted screw with two threaded and two slotted sectors instead of the four we are familiar with in the 3”. The firing mechanism is of the continuous pull type.

The ammunition used is similar to that used with the American and French types of 75s.

• The Principal Parts of the Carriage are:
• Trail
• Top Carriage
• Cradle
• Recoil cylinder
• Springs
• Elevating gear
• Range gear
• Traversing gear
• Firing Mechanism
• Brakes
• Shield
• Axle and wheels
• Sights
• Gravity tank

The trail is tubular. The top carriage houses bearings to receive the cradle trunnions and in travel it is locked to the trail. The bronze cradle pivots on the top carriage. The cradle trunnions support the sight.

The recoil system is of the hydraulic-spring type. The recoil cylinder is surrounded by the counter-recoil springs which in turn are enclosed by a steel case—all of which is screwed on top of the cradle above the gun. The system operates in the same manner as the 3” materiel with the exception that it possesses the additional feature of a gravity tank which replaces oil lost during firing.

75-mm. Gun Carriage, Model of 1917. (British)
Recoil Controlling System

75 mm. Gun Carriage, Model of 1917. (British)
Plan

The elevating mechanism is of the doubled-ended screw type with the independent angle of site. The gears are so arranged that the elevation for range can be made without disturbing the laying for difference in elevation of the gun and the target, that is, the line of sight. The handwheel on the right is for range to the target while the handwheel on the left is for the angle of site.

The traversing mechanism is of the pintle type, consisting of a crosshead, link nut, and an actuating screw with a handwheel. It permits of a 72 mil. traverse either side of the center. A scale strip and a pointer indicate the angle of traverse.

The firing mechanism like that of the American 75 is located on the left side of the gun instead of the right side as on the 3” and the French 75. The gun can be fired when it is within 2 inches of the “in battery” position, which increases the possible speed of firing.

CHAPTER IX
THE 4.7” RIFLE, MODEL 1906.

GUN.

The gun is built up and consists of a tube, jacket, locking hoop and clip. The jacket covers the rear half of the tube and projects beyond the tube at the rear to form the breech recess. The jacket also has a recoil lug on the under side for connecting the recoil cylinder. The clip is a short hoop near the muzzle and has guides formed on it to guide the gun in the cradle on recoil. The jacket also has guides formed on it. The length of the gun is approximately 11 feet.

4.7” Rifle

The breechblock is of the interrupted screw type having four threaded and four plain sectors. It is operated by a handle which swings from left to right turning and withdrawing the breech with one motion. An extractor is fitted for throwing out the shell case when the breech is opened after firing.

The firing mechanism is of the type known as a continuous pull mechanism, that is, the mechanism is cocked and fired by the pull on the lanyard or by downward pressure on the firing handle located at the right side of the breech.

The recoil system is of the hydro-spring type.

The two parallel steel tubes (the spring cylinders) are fitted into a frame surmounted by heavy steel rails which form the gun slides thus forming the cradle. The recoil cylinder is fitted between these two.

The recoil and counter-recoil piston rods are attached to the gun lug and recoil with the gun, while the spring cylinders and recoil cylinder remain stationary.

The recoil is constant, being 70 inches for all elevations. The recoil cylinder uses hydroline oil as the buffer medium. Throttling is obtained by three throttling bars running lengthwise of the cylinder which are of varying height to give a throttling effect with corresponding slots in the recoil piston. A counter-recoil buffer is fitted in the piston rod to take up the shock when the springs return the gun into battery.

The trunnions on the cradle are mounted in bearings formed by a yoke which swivels in a pintle bearing provided at the front of the trail.

Traverse is obtained by means of a handwheel and screw mounted on the left side of the trail which swings the yoke in traverse carrying the gun with it. A traverse of 70 mils on each side of center is possible.

The piece is elevated by a double screw type of mechanism. The upper end is attached to the cradle and so raises and lowers it. The screw is operated thru gearing by two handwheels one on each side of the trail from 5° elevation dep. to 15° elevation.

The trail is of the solid type made up of flasks of channel section. It has housings for the axle and carries the pintle bearing in which the top carriage or yoke swings. A tool box is provided in the trail. A seat is provided on each side of the trail for the cannoneers. The lunette transom is fitted about 27 inches from the rear of the trail and carries a bearing that fits the limber pintle.

A trail prop is provided for supporting the trail when limbering.

The spade can be released and folded up on the trail when traveling.

A traveling lock is provided on the trail for locking the gun when traveling. The piston rod and spring rods must be disconnected before the gun can be drawn back far enough to lock.

The wheels are 61 × 6 inch with rubber tires and band brakes. Some older vehicles have steel tires and are fitted with tire brakes.

An armor plate shield is fitted to the carriage for the protection of the personnel.

The instruments for sighting and laying the piece included a line sight, a rear sight, a front sight, a panoramic sight and a range quadrant.

The line sight consists of a conical point as a front sight and a V notch as a rear sight. These are located on the Jacket of the gun, and are useful for giving a general direction to the gun.

4.7” Rifle

The sighting is similar to the 3”, 1902.

The rear sight and front sight are used for direct aiming. The rear sight is a peep sight mounted on a range scale quadrant by a bracket on right side of the cradle. The front sight is a pair of cross wires mounted in a ring attached by a bracket on the cradle about 3 ft. ahead of the rear sight.

The range scale quadrant has a socket in which the Standard U. S. Panoramic sight may be mounted.

For indirect fire the gunner on the left of the carriage lays for direction only.

On the right side of the cradle is mounted the Range Quadrant which has in combination with it the Angle of Site Mechanism. For indirect fire the gunner on the right of the piece lays for range with this instrument.

Fixed ammunition is used with this gun. Shrapnel and high explosive shell are used. The base fuzed steel shell and the shrapnel weigh 60 lbs. The point fuzed steel shell weighs 45 lbs. Gas shell are also issued identical with the 45 lb. steel shell.

CHAPTER X
THE 155-MM FILLOUX GUN.

155 M.M. GUN MODEL OF 1918 (FILLOUX)

The gun is of the built-up type and consists of the tube strengthened by the following jackets and hoops beginning at the breech end: The breech ring, the jacket, the hoop A, the hoop B, the clip hoop, the clip hoop set on the hoop B and the muzzle bell. The length of the gun from the muzzle to the breech base is approximately 18½ feet.

A recoil lug on the underside of the breech ring provides means of attaching the recoil and recuperator rods. Hinge lugs for the breech are also formed on the breech ring. Bronze clips to serve as guides in the cradle are screwed to the sides of the jackets.

The breechblock is of the interrupted screw type, having four plain and four threaded sectors. The breech mechanism is of the plastic obturator type, having the forward mushroom-shaped head of the breechblock equipped with the asbestos ring, known as the obturator pad. Upon firing, this ring is compressed and acts as a gas check to prevent the leakage of powder gases back through the breech. It has sufficient resiliency to resume its original form after firing. The firing mechanism is of the French percussion primer type which is described under “155-mm Schneider howitzer” and is interchangeable with the guns enumerated therein.

The cradle is a steel forging pivoted by trunnions in the trunnion bearings of the top carriage. It is bored with three parallel cylinders for housing the recoil and recuperator mechanism. On its upper side are slots for the gun slides and the elevating rack is bolted to the lower side.

The recoil mechanism is of the hydro-pneumatic variable recoil type. The larger of the three cylindrical bores in the cradle block contains the recoil mechanism; the two smaller ones, the parts of the recuperator mechanism.

155 MM GUN CARRIAGE MODEL OF 1918 (FILLOUX)
LONGITUDINAL SECTION IN BATTERY

The recoil mechanism consists of a piston and piston rod and a counter rod. The piston rod is connected to the breech lug and, therefore, recoils with the gun. Grooves of variable depth are milled along the length of the counter rod, controlling the flow of oil through the ports of the piston during the recoil. This counter rod assembles within the bore of the piston rod. It does not move longitudinally, but rotates. The amount of this rotation changes the area of the orifices through which the oil can pass. Its rotation is accomplished as the gun is elevated by means of an arm and gear sectors in such a manner as to shorten the recoil as the gun elevates.

A replenisher or gravity tank is provided in connection with the recoil cylinder which assures the recoil cylinder being full at all times and also takes care of any expansion of the oil due to heating. Its capacity is about 17 quarts.

The recuperator mechanism consists of two connected cylinders, one containing the piston and piston rod which are attached to the breech lug, while the other contains a mushroom valve and a diaphragm. The diaphragm separates the oil contained in the first cylinder and part of the second cylinder from the high pressure air which compels the return of the gun into battery after recoil. Normally a small amount of oil must be between the valve and diaphragm. Oleonapth is the liquid used in this recoil mechanism. The amount of oil in the recoil and recuperator mechanism is shown by an indicator so that it can always be seen whether or not they need filling.

The top carriage is a large steel casting mounted on the bottom carriage on which it pivots to traverse the piece.

The handwheels and mechanism for both elevating and traversing, are mounted on the top carriage. The tipping parts are carried on the trunnions of the top carriage.

Belleville Springs carry the weight of the gun when traversing, but on firing the springs compress and the firing stresses are taken on the bearing surfaces between the top and bottom carriages.

The bottom carriage is a large steel casting suspended from the axle (in traveling position) by a heavy multiple leaf spring. It supports the top carriage, houses the axle and provides hinge connections for the trail. When firing the axle is unshackled from the left spring and the bottom carriage bears directly on the axle.

Traversing is accomplished by turning the top carriage which pivots on the bottom carriage. This is done by means of a rack and train of gears which are operated by the handwheel on the left side of the carriage. A traverse of 60 degrees, 30 degrees right and 30 degrees left, is possible.

Elevating is accomplished by a rack on the cradle operated through gears by the handwheel located on the gear box at the left of the top carriage. Elevations from 0 degrees to 35 degrees can be obtained.

The trail is of the split type and consists of steel plate beams of box section. Locks are pivoted at the forward end of the trails for securing them in the open position. When closed together they are clamped and attached to the limber. A traveling lock is provided on the trail for retaining the gun in retracted position.

Two types of spade are pivoted, one for soft and one for hard ground. When traveling the spades are always removed from the trail.

The wheels are of cast steel, each wheel having two solid rubber tires.

Wheel shoes for traveling over soft ground are provided, which assemble over the rubber tires. They consist of twelve plates for each wheel which give a broad bearing surface under the wheel. The wheels are equipped with band brakes.

The sighting equipment is exactly the same as that described with the 155-mm Schneider howitzer.

The ammunition used is of the separate loading type. Either shrapnel or high explosive steel shell is used, as well as gas shells and other special ammunition. The projectile weighs 95 lbs. The propelling charge of smokeless powder is a sectionalized charge made up of two sections; a base charge and one smaller increment. The weight of the charge is 25 lbs.

The fuzes commonly used are the 31 sec. combination fuse for use with shrapnel and combining time and percussion elements: the point detonating fuse Mark IV used with the steel high explosive shell and the mark III point detonating fuze used with gas shell.

155-MM. HOWITZER CARRIAGE, MODEL OF 1918 (SCHNEIDER). TRAVELING POSITION.

155-MM. HOWITZER CARRIAGE, MODEL OF 1918 (SCHNEIDER). RIGHT SIDE VIEW.

CHAPTER XI
THE 155 HOWITZER, MODEL 1918

THE HOWITZER.

General Description.

The 155-mm howitzer, Model of 1918 (Schneider) is of the hydro-pneumatic long recoil type, which may be used for direct fire, but was specially designed for siege fire. On account of its high trajectory it is able to direct shells on targets inaccessible to standard 6-inch howitzers of limited elevation.

This howitzer has given satisfactory results in service and has proven to be more superior than guns of similar caliber. It has a muzzle velocity of 1,480 foot-seconds and attains a maximum range of 12,600 yards, the projectile weighing about 95 pounds.

A maximum rate of fire of four or five rounds per minute may be attained, but heating as well as difficulty of preparing and transporting the ammunition by the gun crew renders such rate impossible for more than a few minutes. However, the normal rate of fire is two per minute and may be loaded at any degree of elevation.

The howitzer is mounted on a sleigh and rigidly secured by means of a breech key and the holding down band. The sleigh contains the recoil and recuperator mechanisms which permits long recoil and insures stability at low elevations. When the gun is fired the sleigh recoils on bronze slides on the cradle, which is a U-shaped steel plate and rests in the trunnion bearings of the trail.

This howitzer may be elevated from 0 degrees to 42 degrees by means of the elevating mechanism. The traverse is 52.2 mils right and left, the carriage sliding on the axle and pivoting on the spade, which prevents the carriage recoiling when the gun is fired. The customary shield protects the gunners from flying shrapnel and fragments.

155 M.M. HOWITZER
MODEL OF 1918
(SCHNEIDER)

In traveling position the howitzer is retracted and locked to the cradle, the cradle locked to the trail, the spade revolved and secured to the bottom of the trail. The lower end of trail rests on the carriage limber, which is used to carry the proportionate share of the load of the howitzer and carriage in traveling position. The limber is equipped with a connecting pole for motor traction. The carriage and limber wheels are rubber tired and considered able to negotiate any roads suitable for field artillery.

Howitzer Description.

The howitzer, consists of a tube and jacket. The jacket is shrunk over, approximately, the rear half of the tube and screwed to it by a short thread near the rear end of the tube. The rear end of the tube is prepared for the reception of the breechblock. On the right of the jacket at its rear are two lugs which receive the hinge pintle of the operation lever. A flat seat with two transverse slots is machined on the top of the jacket at the rear end for receiving the counterweight. The counterweight is securely fastened to the jacket by six screws, and two lugs which engage the slots in the jacket. The bridle is fitted to the underside of the jacket near the rear end and held in place by four screws. The breech key passes through the bridle and holds the howitzer in its seat on the sleigh. On the underside of the jacket just forward of the bridle seat are seven square threads which engage corresponding threads on the sleigh. A holding-down band which encircles the jacket at its forward end also secures the howitzer to the sleigh.

On the top surface of the counterweight are two nickel silver leveling plates.

Vertical and horizontal axis lines are cut on the breech and muzzle faces. A line showing the actual center of gravity with the breech mechanism in place is cut on the upper side of the jacket marked C. of G. The name and model of the howitzer are stamped on the left side of the jacket just below the counterweight. The name of the manufacturer, year of manufacture, serial number of the howitzer and the weight of the howitzer, including the breech mechanism, are stamped on the muzzle face.

155 M.M. HOWITZER MODEL OF 1918
(SCHNEIDER)
BREECH MECHANISM ASSEMBLY

155 M.M. HOWITZER MODEL OF 1918
(SCHNEIDER)
BREECH MECHANISM ASSEMBLY

The breech mechanism is of the plastic obturator, interrupted screw type having four plain sectors and four threaded sectors. The block can be loaded with one-eighth of a turn. Two of the plain sectors are relieved to permit the breechblock to enter the breech recess. The breechblock is screwed into the block carrier and rides on the hub of the latter.

The block carrier is hinged to the right side of the jacket by means of the pintle hinge of the operating lever.

The pintle hinge is fitted at the lower end with an operating lever collar and detent. The dead weight of the breech is carried by the block carrier hinge plate.

The block is rotated by means of a rack which engages teeth cut in the upper surface of the block at its rear end. The rack is actuated by a lug on the under side of the operating lever which engages a slot in the rack. The rack is located in the inside face of the block carrier. When the breech is tightly closed this lock bears against the breech face of the howitzer and is forced back against the rack lock spring leaving the rack free to move. As the breech starts to open the rack lock is forced up by its spring and locks the rack, preventing further rotary motion of the breechblock.

The operating lever is provided with an operating lever handle which is kept in its raised position by the operating lever handle spring. When the breech is closed and locked the lower portion of the operating lever handle engages the block carrier lever catch. When the breech is fully open the operating lever latch which extends through the operating lever, engages the operating lever catch and holds the breech in that position.

155-MM HOWITZER MODEL OF 1918
(SCHNEIDER)
FIRING MECHANISM

The obturator spindle is of the mushroom head type. It passes through the center of the breechblock and is screwed into the front end of the firing mechanism housing, which fits into the hub of the block carrier. The obturator spindle is prevented from turning by the firing mechanism housing key spring. A vent for the passage of the primer flame is drilled through the center of the obturator spindle. The obturator spindle bushing is screwed into the front end of the obturator spindle and the obturator spindle plug into the rear end—the latter forming a chamber for the primer.

The obturator spindle spring bears against the firing mechanism housing and the breechblock, keeping the head of the obturator spindle tightly against the gas check pad. The gas check pad or plastic obturator is composed of a mixture of one part asbestos and three parts nonfluid oil, contained in a canvas covering. The pad is protected by the front, rear and small split rings. A steel filling-in disk is placed between the gas check pad and the breechblock.

The firing mechanism housing is provided with a firing mechanism safety plunger which is forced by the firing mechanism safety plunger spring against the inside circumference of a circular boss on the face of the breechblock. When the breechblock is rotated to its locked position, the plunger slips into a notch in the boss and permits the entrance of the firing mechanism block. When the breech is unlocked the lower end of the firing mechanism safety plunger extends into the firing mechanism housing and obstructs the entrance of the firing mechanism block. This safety device makes it impossible to unlock the breech while the firing mechanism block is in place or to insert the firing mechanism block while the breech is unlocked.

The firing mechanism block is provided with a handle, and screws into the firing mechanism housing. The primer seat plug is screwed into the front end of the firing mechanism block and is provided with a notch into which the primer is inserted. The firing pin guide is located just back of the primer seat plug and forms a guide for the firing pin as well as a bearing for the firing pin spring. The firing pin housing is screwed into the rear end of the firing mechanism block and held in place by the firing pin housing holding screw. The firing pin passes through the firing pin housing and the firing pin guide and is forced to the rear by the firing pin spring. The firing mechanism block is provided with a flange at its outer edge in which a slot is cut to receive a projection on the front of the percussion hammer. This prevents the hammer from striking the firing pin when the firing mechanism block is not screwed home. The firing mechanism block latch is located on the outer face of the block carrier and prevents the firing mechanism block from being unscrewed accidentally.

The firing mechanism block is interchangeable with the firing mechanism blocks used on the following cannon:

155-mm. gun, model of 1918 (Filloux).

8-inch howitzer, model of 1917 (Vickers Mark VI and VIII½).

240-mm. howitzer, model of 1918 (Schneider).

The percussion hammer is carried by the percussion hammer operating shaft which is journaled in the percussion hammer operating shaft housing. This housing is secured to the breech face by means of a dove tail projection which fits into a slot, cut across the entire breech face just below the breech opening. The percussion hammer operating shaft is fitted with a lever at its right end which receives the blow of the firing mechanism striker when the lanyard is pulled. The percussion hammer shaft plunger and spring are located in the percussion hammer operating shaft housing to the left of the hammer. When the breech is open the plunger is forced up by its spring, thereby causing a projection on the plunger to engage in a recess in the operating shaft, locking the shaft so that the hammer cannot be operated. When the breech is closed the underside of the block carrier strikes on the beveled head of the shaft plunger, forcing it down and thus unlocking the mechanism.

The percussion hammer lock bolt is screwed to the face of the carrier to the left of the percussion hammer. Its function is to lock the hammer in the traveling position when the howitzer is not in use.

Operation of the Breech Mechanism. When the breech is closed and locked, the threaded portions of the breechblock mesh with the threads in the breech recess. The operating lever is held by the lower end of the operating lever handle which engages the block carrier lever catch, thus preventing any rotary motion of the breechblock at the instant of firing. The firing pin receives the blow of the percussion hammer and fires the primer. The flame passes through the vent in the obturator spindle, igniting the propelling charge. The gas pressure in the bore forces the mushroom head of the obturator spindle hard against the gas check pad causing the latter to expand and press against the walls of the chamber, forming a gas-tight joint. After the explosion the elasticity of the pad causes it to resume its former shape, allowing the obturator to be withdrawn freely from its seat when the breech is unlocked.

To Open the Breech. After the piece has been fired, and before unlocking the breech, press back the firing mechanism block safety latch, screw out the firing mechanism block and remove the used primer. The breech can not be unlocked with the firing mechanism block in place. An attempt to do so will result in jamming of the firing mechanism safety plunger. It is therefore important that the firing mechanism block should be removed before attempting to unlock the breech.

Press down on the handle of the operating lever in order to disengage it from the block carrier lever catch. Move the lever toward the rear and then to the right. In the first part of this movement, the operating lever turns freely around the hinge pin and its lug operates the rack which turns the breechblock. The threaded parts of the breechblock are thus disengaged from the threads in the breech recess. As the rack reaches the limit of its travel, the block carrier is swung on its hinge drawing the breechblock out of the breech recess. As the block carrier leaves the breech face of the howitzer the rack lock is forced by its spring into the recess in the rack preventing any further rotary motion of the breechblock in either direction. As the breech reaches its full open position the right end of the operating lever catch engages the operating lever catch, locking the breech in open position.

In loading, care should be taken to ram the projectile home and to enter the propelling charge in such a way that the igniter of the base charge will be in contact with the mushroom head of the obturator spindle when the breech is closed.

To Close the Breech. Press down on the operating lever handle to disengage the operating lever latch from the operating lever catch and move the operating lever to the left and forward. As the block carrier comes in contact with the breech face of the howitzer, the rack lock is pushed back into its seat, freeing the rack. Further movement of the operating lever forces the rack to the left, rotating the breechblock until its threaded portions mesh with the threads in the breech recess. At the end of the movement of the operating lever, the operating lever handle engages the block carrier lever catch and fastens the breech in locked position.

Insert a new primer in the primer seat plug and replace the firing mechanism block. The firing mechanism block can not be entered until the breech is closed and locked. Any attempt to do so may cause damage to the firing mechanism safety plunger or some part of the firing mechanism.

THE CARRIAGE.

For the purpose of description, the carriage is considered as composed of the following groups: Sleigh (including recoil mechanism), cradle, trail, traveling lock, elevating mechanism, traversing mechanism, wheels, road brake, and shield.

The sleigh contains the recoil and counter-recoil mechanism and serves as a support for the howitzer, being secured to it by the breech key and the holding-down band. The recoil counter-recoil cylinders, and two air cylinders are bored in the sleigh and form the recoil mechanism. The ends of the recoil and counter-recoil cylinders are attached to the cradle and when the howitzer is fired the sleigh and howitzer recoil, sliding on the cradle sides.

The holding down band is anchored on either side to the front band clips, which are secured to the sleigh. Grooves are cut underneath the two top edges of the sleigh, and are lined with bronze liners, known as sleigh slides. These liners slide on the cradle clips and guide the howitzer during recoil. Five longitudinal cylinders are bored in the sleigh, the two upper cylinders running about one-third the length of the sleigh, forming air tanks and are closed at the front end by the air tank heads. The left air tank head is provided with an opening in which the gage-cock body is assembled. A pressure gage may be assembled through an adapter to this gage-cock for ascertaining the pressure in the counter recoil system. The gage-cock is also provided with a pointer which registers the quantity of liquid in the system on a scale provided on the air tank head. The two lower cylinders extending the full length of the sleigh, form a housing for the recoil mechanism, the right cylinder being the counter-recoil cylinder and the left the recoil cylinder. The small equalizing cylinder in the center of the sleigh, extending only a short distance, is closed at the front end with the filling valve, through which air or liquid is introduced into the system.

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
SECTION, IN BATTERY

The counter recoil cylinder is connected by a passage to the right air tank and also to the small equalizing cylinder, the latter being connected to the left air cylinder, thus maintaining equal pressure in both air cylinders and in the counter-recoil cylinder. The counter-recoil cylinder is closed at the rear end with the counter-recoil cylinder head and at the front end with the stuffing box, through which the counter-recoil rod and its piston moves. The recoil cylinder is closed at the rear end with the recoil cylinder head and at the front end with the recoil cylinder stuffing box, through which the recoil piston rod operates. This rod is hollow and serves as a buffer chamber for the buffer rod, which is securely screwed to the recoil cylinder head at one end, the other end carrying the counter-recoil valve. The recoil and counter-recoil rods are fitted with the piston rod nuts on the front end which engage the piston rod lock plate.

The cradle is a steel U-shaped plate reinforced by several transoms and supported by the trunnion bracket, elevating segment brackets, and in traveling position by the cradle band which engages the clips on which the howitzer recoils when in action. The sleigh traveling locks are mounted at the extreme ends of the cradle and used to lock the sleigh to cradle when the howitzer is in traveling position.

The cradle is mounted on trunnions on the carriage, and by means of elevating segments geared with the elevating mechanism may be inclined at various firing angles. When carriage is traveling the rear end of the cradle rests on the cradle traveling lock, thereby relieving the elevating mechanism of the weight of the howitzer, sleigh and cradle.

The left trunnion of the cradle is bored out to receive the sight and bracket. The shoulder guard is located on left side of the cradle just back of the trunnion bracket and protects the gunner from the recoiling parts. The firing mechanism is located on the right side of the cradle and provided with a safety device which prevents the piece from being fired when the piston rod nuts are not engaged by piston lock.

The recoil indicator is located just back of the trunnion bracket on the right side of the cradle and consists of a steel spring which is adjusted by means of a nut so that the pointer bears against a scale engraved on the edge of the sleigh indicating the length of recoil. The front end of the cradle is covered by the cradle head and provided with an opening through which the pressure-gauge adapter may be assembled to the gauge-cock body. The lower half of the front end of the cradle is closed by the front transom, forming a guide for the piston-rod lock which is operated by means of a lever. When this lever is lowered the lock plate moves to the right, releasing the piston-rod nuts. When the lever is raised the lock moves to the left, locking the nuts in firing position. The locking device is protected by the cradle front cover which holds the lever in firing position when closed. The filling valve is accessible through the cradle bottom cover located on the bottom of the cradle to the rear of the front transom. The pump bracket is located on the left side of the cradle near the front.

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
LEFT SIDE ELEVATION, IN BATTERY

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
ELEVATING MECHANISM

Recoil and Counter-Recoil Mechanisms. When the howitzer is fired the recoil mechanism exercises its retarding influence by means of a liquid which is obliged to pass through an orifice whose size diminishes as the movement proceeds, thus checking the recoiling mass. The recoiling movement of the gun actuates at the same time the counter-recoil mechanism, which acts on the counter-recoil liquid and forces it into two reservoirs, thus further compressing a gas therein contained. When the recoil movement is ended the expansion of gas forces the counter-recoil mechanism back “into battery,” and the recoil cylinder again exercises its retarding influence to prevent a too rapid return and shock. The normal recoil is 51.375 inches (1.305 meters).

When the piece is fired the howitzer and sleigh move to the rear, the recoil and counter-recoil rods, which are held by the piston-rod lock remaining stationary. The liquid in the counter-recoil cylinder is thus forced into the air cylinders, building up a pressure sufficient to return the howitzer to battery. The liquid in the recoil cylinder is forced through the orifices in the recoil piston rod and then through the throttling ring. The tapered buffer rod, which is attached to the recoil cylinder head, moves through the throttling ring, gradually closing the orifice, thus keeping the pressure constant as the velocity of recoil is reduced. As the buffer rod moves to the rear the counter-recoil valve is opened, allowing the liquid to pass freely into the buffer chamber. As the gun returns to battery the buffer valve closes, forcing the liquid to pass through the small clearance around the valve, thus absorbing the energy of counter recoil.

By means of the elevating mechanism the howitzer, sleigh and cradle are inclined at the various firing angles, varying from zero to 42 degrees, by rotation in the trunnions of the cradle.

Two elevating segments attached to the cradle are actuated by the elevating pinion shaft operating in bearings integral with the elevating worm wheel case secured to trail. To lower end of worm shaft is fitted a worm which engages a worm wheel and pinion shaft in the gear case. On upper end of worm shaft is attached the elevating hand wheel fitted with a handle and plunger enabling the operator to lock the howitzer at any desired elevation. The motion of the handwheel is transmitted through the worm gear to the pinion shaft and thence to the elevating segments.

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
TRAVERSING ROLLERS

The handwheel is provided with a handle of a spring locking type, downward pressure on which unlocks it from the handwheel latch plate, permitting the mechanism to be operated.

Traversing Mechanism. The traverse of the carriage is obtained by means of the traversing mechanism causing the carriage to slide on the axle, the trail pivoting on the spade. The movement is 3 degrees each side of center or a total of 105 mils.

At the center of the axle is rigidly attached a bronze traversing nut through which passes the traversing screw which may be operated from either side of the carriage by means of handwheels connected to the screw through bevel gears and shaft. The traversing screw operates in the travelling housing longitudinally and held in position by thrust bearings and thrust bearing adjusters at both ends of the screw. When either of the handwheels is operated the traversing screw is rotated and moves to the right or left as the case may be, carrying the entire carriage which moves across the axle on traversing rollers.

In order to reduce friction during the traversing operation the carriage rests on the axle through Belleville springs and two concave faced traversing rollers mounted on roller shafts in the axle housing. When gun is fired the Belleville springs are compressed and the carriage rests on the axle through the bronze traversing roller boxes.

On top of axle projecting to the left of carriage is riveted an azimuth scale graduated in mils so that the position of the carriage on the axle may easily be seen at any time. When in traveling position the carriage should be locked to the axles by the axle traveling lock, thus relieving the traversing mechanism from unnecessary stress.

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
TRAVERSING MECHANISM

The axle traveling lock is a device employed to relieve the traversing mechanism from unnecessary stress when the carriage is in traveling position. When the carriage is prepared for traveling the traveling lock engages a series of square grooves cut in the center of the axle. The lock is operated by an eccentric on the end of the traveling lock shaft which is controlled by the lock lever fixed on outer end. The lock lever may be placed in two positions marked “to travel” and “to fire,” by means of its handle which is provided with a spring plunger engaging the traveling lock catch. In order to properly lock the carriage in traveling position it is necessary to traverse the carriage to the center position on the axle, thus permitting the locking device to engage the grooves cut in the center of the axle.

The air pump is furnished for the purpose of charging and maintaining the necessary pressure in the counter recoil reservoirs. When in operation it is attached to a bracket on the carriage by means of a screw clamp and connected to the reservoir by the filling pipe. The pump will operate against a pressure of 400 to 600 pounds per square inch.

The liquid pump is a single-acting-plunger used for charging the counter-recoil system and for the purpose of replenishing losses of liquid from the cylinders. Power is applied through a hand lever connected by parallel links and a cross-beam at the lower end of the piston. The hand lever is detachable and also used in connection with the air pump. When in operation the pump is attached to a bracket on the carriage by means of a screw clamp. The filling pipe is employed to connect the liquid pump with the recuperator cylinder.

The reservoir for compressed gas is a commercial seamless cylinder with a capacity of 2,842 cubic inches and is charged with nitrogen gas at a working pressure of 2,000 pounds per square inch (140 kilograms per square centimeter). The reservoir is provided with a needle valve and a connection for the pressure gage or filling pipe. This cylinder is used for charging the counter-recoil system and may be carried on the artillery supply truck furnished with 155-mm organizations.

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
AIR AND LIQUID PUMPS

155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
TRAVELING POSITION

The filling pipe is used to connect the counter-recoil reservoirs with the air or liquid pump or with the compressed gas reservoir.

Pressure Gage. The gage for the compressed gas reservoir is calibrated from 0 to 150 kilograms per square centimeter. It is used to ascertain the pressure of gas in the reservoir and must be attached before screwing on the filling pipe. The gage for the pressure-gage adapter is calibrated from 0 to 60 kilograms per square centimeter, is screwed into the side of the adapter and used to test the pressure in the counter-recoil system.

The quadrant sight, model of 1918 (Schneider), is mounted on the left trunnion of the carriage, both in traveling and in action, and should not be removed by the battery mechanics. The principal features of the quadrant sight are: The cross-leveling mechanism, the elevating mechanism, and the angle of site mechanism.

The cross-leveling mechanism principally consists of the leveling worm, leveling stop, antibacklash spring, leveling clamp, and cross levels. By means of the cross-leveling mechanism the quadrant sight is adjusted to proper alignment with the bore of the howitzer.

The bracket fits into the trunnion on the left side of the carriage and is provided with four tennons which engage slots in the face of the trunnions keeping the sight in proper alignment with the bore of the howitzer. The bracket is screwed in place by the bracket bolt; the front end of the body of the quadrant sight fits into the cylindrical part of the bracket and is held in place longitudinally by four lugs.

QUADRANT SIGHT, MODEL OF 1918.
(SCHNEIDER)

The body of the sight is rotated by the leveling worm engaging the worm segment cut on the under side of the body. The outer end of the worm is provided with a knurled hand wheel by means of which the leveling mechanism is operated. The leveling stop, secured to bracket, engages slot in the body, thus limiting the angular motion of the body in either direction. The rear end of the cylindrical part of the bracket is split and provided with a leveling clamp by means of which the body may be locked in position after it has been leveled.

The cross level is located on the rear edge of the sight shank and serves the gunner in determining the level position of the instrument. The level vial is a glass tube, closed at both ends, and partially filled with a liquid consisting of 4 per cent alcohol and 60 per cent ether, a small bubble remaining in the tube. Graduations are etched on the circumference of the tube to indicate the central position of the bubble. The vial is held in a level-vial tube, the ends being wrapped in paper and set in plaster of paris. The knurled cross-level cover fits over the holder and, together with the level-vial tube, are held in place by the cross-level caps, which close the ends of the holder. When closed, the cover serves as a protection for the vial.

The elevating mechanism consists principally of a sight shank, elevating worm wheel, antibacklash pinion, elevating worm, elevating worm eccentric, elevating scale drum, and scale drum housing.

NOTES ON CARE OF THE 155 HOWITZER.

The executive should be perfectly familiar with the working of the recoil and know when to put a gun out of action due to faulty recoil. The length of the recoil should be such that the end of the gun slides do not recoil over the end of the cradle rails. In counter-recoil, the sleigh should be perceptibly slowed down at a point about 10 centimeters from the front of the cradle, and from there on should ease gently into battery without a sound or shock. Strict watch should be kept to see that no excessive leakage takes place through the stuffing boxes, the valve in the gauge adapter, or the oil hole in the cylinder end nut. Slight leakage can hardly be helped, as one of the stuffing boxes is under more than four hundred pounds of pressure per square inch when the gun is at rest, and three or four times that amount when the gun is in full recoil. However, if a pool of liquid is found after the gun has been standing all night, it is time to report the matter and have the packings replaced. The gun must be dismounted, the stuffing-box repacked, and the dermatine inspected. The dermatine packing is a compound resembling rubber, but it has the quality of resisting any chemical action that the liquid may set up in the recuperator. A worn dermatine packing may be replaced by the simple expedient of turning it wrong side out and then using it again as before. This has actually been tried and found to give good results. Another temporary repair was effected by cutting a ring from a solid truck tire and using it in the place of the dermatine, until a packing of the latter could be obtained.

The French obtain a very tight fit in their stuffing boxes by the peculiar design that allows the liquid pressure to actuate a strong spring which in turn expands the packing against the rod or cylinder wall. Leakage through the recuperator stuffing box will be noticed by the liquid coming out of the oil hole in the right-hand cylinder end nut.

In dismounting French materiel, care must be used to replace the same nuts on the bolts from which they were taken. Threads are not standardized as to diameter; hence, trouble is likely to occur when remounting.

To dismount the tube from the recoil mechanism, or sleigh as it is denoted, a suitably strong overhead beam is selected and the carriage run beneath it. Mount two one-ton duplex blocks on the beam over either end of the tube and thread the bore with a half-inch wire cable sling, in such a manner as to leave a bight at both muzzle and breech ends. Into these loops the hooks of the block catch. Gunny sacks form a suitable packing at the muzzle and breech to prevent the cable damaging these parts of the tube. Provide several blocks of two by four or four by four stuff, to block up the sleigh as it is moved to the rear—as we shall soon see that it does. Remove the locking hoop by knocking out the retaining bolts, and also remove the cradle bolts from their housing on the cradle. This will allow the sleigh to move to the rear of the cradle. Take a strain on the blocks and carefully move the sleigh back over the trail until the recoil-lug key (locking the recoil lug to the sleigh) clears the end of the cradle. Remove the set screw from the bottom of the sleigh which locks the tapered key in place, and proceed to drive the key out with a sledge hammer and a block of wood. During this operation the rear of the sleigh must be blocked up on the trail in order to take the strain off the cradle rails. After the key is cleared, the tube may be raised by means of the two blocks, care being taken to make the lift vertical, otherwise the slots and grooves just in front of the breech will jam and be damaged. Remove the carriage and lower the tube onto blocks. The process of mounting is just the reverse of the above.

The elevating and traversing mechanisms give little trouble, if all gear cases are kept packed in grease. It is extremely important that, in laying for elevation with this piece, the final turns of the handwheel should bring the gun into correct position by raising the breech and not by lowering it. In this way all backlash is taken out of the gearing and the howitzer rests solidly for firing. The gunner may easily be taught to remember this by always having him bring the range bubble to the front of the glass and then slowly elevate the breech, bringing the bubble to him.

The traversing mechanism moves the whole carriage, including gun, along the axle, about the spade as the center of rotation. The traversing screw moves the carriage by being rotated through nut set solidly in the axle. The axle and nut are stationary and the screw moves laterally by means of the traversing handwheel. Hence, the carriage being attached to the screw, must move when the screw moves. Inasmuch as the axle is straight, it must accommodate itself to the arc of the circle described about the spade as the center. It does so by moving tangent to the arc, and consequently one end moves to the front and the other end moves to the rear, carrying the wheels with them. From this it will be seen that before attempting to traverse the piece, the brake must be “off.” The movement of the wheels may be easily seen, if a pencil line be drawn across the tire just above the brake shoe and then the piece traversed. The line will be seen either to raise or lower according to whether the piece be traversed to the right or left.

In filling the “brake” or recoil cylinder, good results have been obtained by merely leveling the gun and filling the brake cylinder until full. Trying to pour out one hundred cubic centimeters of the liquid after the brake is full, as the French drill regulations lay down, is almost impossible; and no bad effects will be noticed provided the gun does not become excessively warm during the firing. If it should become warmed up sufficiently to affect the recoil, level the gun, unscrew filling plug to release the pressure, rescrew, and continue the fire. In using the manometer gauge, to measure the pressure and the height of the liquid in the recuperator, it will be found that the valve in gauge adapter will sometimes stick open to the extent of letting out all the air in the recuperator tanks. The only sure remedy for this is entirely to dismount the gun, remove the adapter, and replace its valve packing, which no doubt will be found to be worn and frayed, or else some foreign substance will be found to be lying between it and its seat. The gauges should be tested about once in three months by means of a standard steam gauge testing apparatus, making the appropriate transformations if the tester be graduated to pounds per square inch as most steam testers are. It will be found that the maximum steam pressures used are rather lower than these gauges read, hence only the lower readings may ordinarily be tested.

To set the pointer to the correct pressure reading, pull the pointer loose and apply a known pressure to the gauge. Set the pointer at the corresponding reading on the manometer and press it on tightly. In general, this is sufficient for practical work.

After each firing the breechblock should be entirely dismounted and each part washed in caustic soda solution and then stippled with oil before reassembling.

The wheels are made of smaller members than those that we are accustomed to see in our own materiel. It must be remembered, however, that the French designed their wheels for much better roads than ours; and, in comparison with our materiel throughout, this fact must be borne in mind. The wheels must be carefully watched, especially through the dry weather, for they tend to check and crack. Remedies are tire shrinking and soaking in water over night, followed by a thorough and careful application of linseed oil. Fast travel, as when the piece is coupled to a truck, must be avoided if the life of the carriage is to be assured.

According to the French drill of the gun squads, in going into action, the piece is first unlimbered and the trail is then laid on the ground, and the cannoneers change posts to the extent of the gunner going to his position by his sight; while the remaining cannoneers lift the trail again and set the spade. This is slow and cumbersome work. Much better results may be obtained by setting the spade at the time that the piece is unlimbered, without moving the cannoneers from their posts.

CHAPTER XII
EXPLOSIVES, AMMUNITION AND FUSES.

EXPLOSIVES.

As a matter of practical interest, explosives may be divided into three classes, namely:

(1) Progressive or propelling explosives called low explosives.

(2) Detonating or disruptive explosives, termed high explosives.

(3) Detonators or exploders, known as fulminates.

The first includes all classes of gun powders used in firearms of all kinds; the second, explosives used in shell, torpedoes, and for demolitions; the third, those explosives used to originate explosive reactions in the two first classes. Corresponding names are given to the phenomena characteristic of each class of explosives, (1) explosions proper, of low order, progressive, or combustions, (2) detonations, of high order, (3) fulminations, this last possessing exceptional brusqueness.

The explosion of low order is marked by more or less progression; the time element is involved as a controlling factor, the time required to complete the explosive reaction being large compared with that of the other forms of explosion.

The second class of explosion is of a different nature. The explosive reaction is not limited or confined to the surfaces exposed but appears to progress in all directions throughout the mass radially from the point of initial explosion. It has been determined experimentally that the velocity of propagation of the explosive wave throughout a mass of guncotton is from 17,000 to 21,000 feet per second.

Fulmination is a class of explosion still more brusque than the last. The abruptness of their explosion and the consequent sharpness of the blow and the concentration of heat on the point of ignition constituting their efficiency as originators of explosions of the first two classes.

Methods of Exploding. Explosives may be exploded by three methods; in reality but two, by heat and by application of energy as by a blow. The heat may be applied directly by friction, by electricity and detonating cap, these two methods of applying the heat giving rise to the three practical methods above mentioned. As it is not practical to apply heat directly to the charge, small charges of special explosives are made up into primers and these are exploded in one of the ways above mentioned and so communicate the explosion to the main charge. Fulminate of mercury is one of the high explosives fulfilling the requirements and it is readily exploded by any one of the methods mentioned. It is used in all detonating caps. Primers for cannon also contain an additional charge of black powder to increase the flame. For this purpose also igniting charges of black powder are attached to the smokeless powder charges for the larger calibers.

Uses. The chief use of low or progressive explosives is as a propelling charge in guns and for blasting where it is desired to exert a pushing effect rather than a blow. High explosives are used when it is desired to exert a high pressure and shatter the container, as in a shell, mine, etc. This class is not satisfactory as a propelling charge for the reason that its rapidity of action is so great that the pressure exerted would burst the gun before the projectile could start. Low explosives are not satisfactory shell fillers for the reason that their action is so low that the shell would break at its weakest point before all the explosives had exploded and what remained would be wasted. With a high explosive, all or most of the charge explodes before the shell can break up. The greater the rapidity of action of an explosive the finer the fragmentation of the projectile. With too rapid action the pieces are too small; with too slow action they are too large. Experience teaches the proper rapidity of action to attain the fragmentation most efficient against animate and material targets.

Propelling Charges. Up to the present time nitrocellulose powder has complied better with the requirements of a suitable, smokeless powder than any other that has been proposed and is used in our service for propelling charges in guns. The danger of manufacture is also less than that of nitroglycerine powders. Moreover the latter, which was formerly used in our service and still is in the British and some others, causes too much erosion of the tubes due to the greater heat of explosion. It has the advantage of requiring a smaller charge for the same muzzle velocity and therefore a smaller powder space and consequent lighter weight of gun.

Shell Fillers. High explosives for shell fillers. Up to the present explosive “D,” trinitrotoluol and picric acid are the principal high explosives which fulfill the requirements as shell fillers. Explosive “D” on account of its great insensitiveness to shock is used in armor piercing projectiles and also in field gun and howitzer shell. It is detonated by a fuze. Trinitrotoluol is used in submarine mines and in general demolition work as it is much easier to explode than explosive “D.”

Table of Explosives. The following table gives a good idea of the principal explosives in use in our service and the characteristics of each:

High Explosives. The principal high explosives used as shell fillers in our service are: picric acid, explosive “D” and trinitrotoluol, or more popularly known at TNT. The picric acid and picrates used as shell fillers are secret compositions. Mellinite, essentially picric acid alone or with some other substance is used as a shell filler by the French. It is poured into the shell in a fused state and allowed to harden, thus giving a very compact charge and one easily handled. It has the disadvantage however of forming unstable compounds with the metal of the shell and great care must be exercised in coating the interior of the shell with a protective coat before pouring in the fused mellinite. Lyddite is the English equivalent of mellinite. Picric acid was also used by the Japanese or it may be a mixture of picric acid and some nitro compound. The most successful explosive of this type is explosive “D” invented by Colonel Dunn of our Ordnance Department and sometimes known as “Dunnite.” It is not fusible and must be compressed for use as a shell filler, being forced into the shell by compression. This is a disadvantage as compared to mellinite as the density of loading is less and weight for weight therefore less efficient. It is little sensitive to shock and therefore not very dangerous to load even under great pressure. Trinitrotoluol is also used as a shell filler but its chief use is in demolition work and as the charge for submarine mines.

Nitrogen Compounds. It may be interesting to note that all of the principal explosives with which we have been dealing are compounds containing nitrogen. In fact the war has been fought with fixed nitrogen which explains the great interest taken in the various attempts to fix the free nitrogen of the air which is the world’s great storehouse of free nitrogen. As nitrogen is also a necessary ingredient in the various fertilizers, the result to the world of a commercial process for speeding up the cycle of changes through which nitrogen passes in its life giving mission from free nitrogen in the air to its various compounds in the nitrogeneous animal and vegetable tissues is almost limitless and as usual war has been the incentive to speed up a process which will result in incalculable value to mankind.

Classification. Guns are loaded with three kinds of ammunition: fixed, semi-fixed and separate loading ammunition. In fixed ammunition the round is complete and projectile and powder loaded into the chamber at the same time. In semi-fixed the projectile is separate from the powder charge, which however is put up and loaded into the chamber in a container. In separate loading ammunition the powder is loaded into the chamber in bags. In the first two cases the cartridge case furnishes the means for sealing the rear of the powder chamber against escape to the rear of the powder gases. In the last case some form of obturating device is made a part of the breechblock furnishing a gas check to seal the rear of the powder chamber.

Fixed Ammunition. All of our field guns below 5 inches in calibre use fixed ammunition. The powder is placed loose in the cartridge case, the space not filled with powder being stuffed with packing paper, excelsior, or felt wadding next to the projectile so as to hold the powder in contact with the primer, in some fixed ammunition a brass diaphragm is soldered to the inside of the case for the same purpose and to keep out moisture, (4.7” Gun). An igniting charge of black powder is a part of the primer and in some cases an additional charge is placed at the forward end of the powder space in the cartridge case to insure rapid ignition of the smokeless powder. In this case it is held in place between two quilted disks of crinoline.

Semi-fixed ammunition is employed in our 6” and 4.7” field howitzers. The cartridge case contains three weights of propelling charge for firing in the three zones designed to give a high angle of all with these weapons. Access to the charge is had by tearing off the brass diaphragm closing the forward end of the cartridge case. By removing the first charge the remaining charge is that prescribed for the second zone, and by removing the top two charges the remaining charge is that of the first zone. The three charges are tied together and the middle charge has an igniting charge of black powder attached. The removal of charges is facilitated by the separate container for the powder charge and the round is more easily handled in the two parts especially in the case of the six-inch howitzer, where the projectile weighs 120 lbs. The same primer is used as in fixed ammunition, the cartridge case performing the function of an obturator.

BREECH MECHANISM OF 155 GUN SHOWING
DE BANGE OBTURATOR.

Separate Ammunition.—Obturation. The 155-mm Filloux gun and 155-mm howitzer use separate ammunition. In such guns there must be provided some form of a gas check which will prevent the powder gases from rushing to the rear into the threaded portion of the breechblock, as this would soon erode the thread sectors and render the gun useless beside losing a large amount of pressure in the bore. The device used as a gas check is called an obturator. There are two systems of obturation in use, named after their inventors:

The DeBange and the Freyre. The former is used in the 155’s. It consists of a steel mushroom head closing the rear of the powder chamber, the spindle of which passes through a central hole in the breechblock. Between the mushroom head and the face of the breechblock is a pad of asbestos, paraffine and tallow, pressed into shape by a hydraulic press and covered by canvas or asbestos wirecloth. Split rings having hardened outer surfaces are fitted, one just behind the mushroom head and one just in front of the face of the breechblock. Their diameter is slightly greater in the free state than the conical surface of the bore where they bear when the breech is closed so that they always close the rear of the powder chamber. The pressure of the powder gases forces the mushroom head to the rear and this compresses the asbestos pad which in turn forces the split rings to bear with greater force against the walls of the powder chamber thus securely closing the rear opening of the powder chamber. For more details of this device see pages 302 to 306 Tschappat’s O & G.

Powder Bags. Cartridge bags for separate loading are made of raw silk, and are sewed with silk thread. Other materials are apt to produce flare-backs or premature explosions because they are not entirely consumed in the bore or continue to burn if not consumed. The raw silk however either is entirely consumed or if not, the parts ignited immediately go out as soon as the flame is removed and do not smoulder. Specially treated cotton fibre bags have been tried but so far as I know have not as yet superseded the raw silk for the purpose. The gases remaining in the bore after the discharge of a charge of smokeless powder are explosive and with air form an explosive mixture, hence the danger upon opening the breech if any smouldering particles remain in the bore.

21 GRAIN PERCUSSION PRIMER MARK II-A

Primers. The devices for initiating explosions of propelling charges in military guns are called primers. With fixed and semi-fixed ammunition the primers are seated in the base of the cartridge case. In the case of separate loading ammunition the primers are inserted separately in the breechblock, the expanding gases of the detonated primer forcing the walls of the primer case tightly against the bore through the breechblock and thus sealing this channel of escape for the gases from the powder chamber. This necessitates a much larger and stronger case for separate loading primers than for those inserted in the base of a cartridge case.

Classes of primers. Primers are divided into three classes according to the method by which they are fired: (a) friction primers, (2) electric primers, (3) percussion primers. Combination primers are made which may be fired by any two of these methods, usually electric and one of the others. The characteristics of a good primer are, certainty of action, safety in handling, no deterioration in storage, simplicity in construction and be cheap to manufacture. They are also divided into obturating and non-obturating depending upon whether they close the vent during discharge or not.

Primer pressing. Primers for fixed ammunition are inserted in the base of the cartridge cases by means of a special press for this purpose. The primer body is a trifle larger than the seat in the cartridge case provided. This seat is rough bored to a diameter less than the finished size and then mandreled to finished dimensions with a steel tapered plug. This process toughens the material of the case around the primer seat and prevents the expansion of the primer seat under pressure of the expanding gases.

Percussion primers. Except for very heavy siege guns and railroad artillery the guns handled by the Field Artillery use percussion primers. The 110-grain percussion primer is the one in use in our service and as typical will be described. The charge consisting of 110 grains of compressed black powder makes the charge burn like a torch rather than explode, which facilitates the ignition of the charge of smokeless powder, with which the flame comes in contact. The diametral holes spray the flame in several directions thus insuring ignition at many points simultaneously. The percussion element consists of a percussion primer cup, the percussion composition and an anvil, all of which are assembled together in a cup in the rear face of the primer case. The percussion composition is made up of chlorate of potash, sulphide of antimony, ground glass and sulphur. A blow upon the cap by the firing pin detonates the percussion composition and the flame from this detonation ignites the black powder which in turn explodes the charge of smokeless powder.

The General Shape and Nomenclature of Projectiles.

The reason for the particular shape of shells may not be clear to all. In the first place all matter has the property known as inertia, which we may define as that tendency of matter to remain in a state of rest or to continue at a uniform velocity if in motion. It offers a resistance to any change in the state of either rest or motion whether of amount or direction. Consequently when we apply a sudden and tremendous force to the base of a projectile by means of the expansive force of exploding powder gases, there will be set up in the metal a resistance to this force in which every particle of the projectile will resist by an amount proportional to the mass of particles beyond the point of application of the force to itself. The actual force will be proportional to the weight and acceleration produced by the applied force in the projectile. This explains the reason why the walls of the projectile are thicker near the base. It also explains the method of calculating the thickness of walls, for if we know the weight at any cross section and the co-efficient of strength of the metal we may calculate the thickness of walls necessary to withstand the pressure for any given muzzle velocity which is fixed by other considerations. It explains also the preference for steel in projectiles as for the same weight the steel is much stronger making it possible to throw a greater amount of shrapnel or high explosives in shell.

155-MM COMMON STEEL SHELL MK IV

The necessity for compact loading, especially in the case of high explosive shell is also noted as otherwise the shock due to inertia would break up the charge and perhaps cause a premature explosion. Hence it is very necessary to guard against airholes in filling shell cavities.

In order to secure regular and uninterrupted movement of the projectile through the bore it is necessary that the projectile and bore have the same geometric axis. Also the projectile must be seated exactly and uniformly for succeeding rounds in its seating in the bore. This latter is necessary in order that the powder chamber may not vary as this would give irregular pressures. The liability of strapping the rotating bands or setting off the fuze in certain kinds of fuzes are also explained by inertia. It might even cause sufficient shock to detonate the charge in the shell. The remedy is accurate seating of each projectile by reason of trained gun crews using the same amount of force at each ramming. The first condition, coincidence of axes, is obtained by means of the ogival head which has a diameter some tenths of a millimeter smaller than the diameter of the bore, and serves as a front support for the projectile while the rotating bands center it in rear. Were it not for the bell the projectile, held only by the soft material of the rotating band, would wabble in its travel through the bore and tumble soon after leaving it. It is also necessary that the center of gravity of the projectile be on its geometric axis. Otherwise it will travel on a spiral of the same pitch as the grooves and knock the tube walls as it travels through the bore and without the support of the bell might cause a premature explosion by actuating the fuze.

155M/M SHRAPNEL—95 LBS.—MARK-I.

COMMON STEEL SHELL MARK I.
COMMON STEEL SHELL MODEL OF 1905.
SHRAPNEL.
CARTRIDGE CASE.
4.7” Gun Ammunition.

Three-inch Ammunition.

Fixed ammunition is used in the 3” field guns, and is made up with either common shrapnel, high explosive shrapnel, or common steel shell. The rounds as made up vary in length with the type of projectile used. The ammunition chests of the battery are of sufficient size to take any one of the rounds furnished, so that the number of each kind to be carried is a matter for regulation by proper authority. Each round is issued with projectile filled and fused. The weight of the projectile is 15 pounds, and the total weight of one round is 18.75 pounds. The components of one round are the cartridge case with primer, the powder charge, igniter, projectile and fuze.

The cartridge case.—The cartridge case is a solid drawn-brass case 10.8 inches long; it has a capacity of 66.5 cubic inches, and weighs, with primer, 2.25 pounds. A circular groove is cut in the base of the cartridge case and the groove is painted red for high explosive shrapnel, yellow for common shrapnel, and black for high explosive shell.

The primer.—The percussion primer, known as the “110-grain percussion primer,” contains an igniting charge of 110 grains of black powder in addition to the essential elements of a percussion primer. The purpose of the black powder is to insure the ignition of the smokeless powder charge in cartridge case.

Common Steel Shell.
Common Shrapnel.
Cartridge Case.
Semple Tracer.
High Explosive Shrapnel.
3” AMMUNITION

The powder charge.—The powder is a nitrocellulose powder composed of multiperforated (7 perforations) cylindrical grains, each 0.35” long and 0.195” in diameter. The charge varies slightly for different lots of powder, but is approximately 24 ounces. The charge gives a muzzle velocity for shrapnel of 1,700 feet per second (1600 f/s for shell) with a maximum pressure in the bore not exceeding 33,000 pounds per square inch. At the front end of the cartridge case there is an igniter of black powder weighing about ¼ oz. which assists in the uniform ignition of the smokeless powder charge.

The projectiles.—All projectiles have a copper rotating band 1.2” from the base. This band engages in the rifling of the bore of the piece, and gives the projectile a rapid rotation about its long axis during flight. This causes it to travel straight, point on, without tumbling.

Common shrapnel.—The common shrapnel is a base-charged shrapnel fitted with a combination fuze. The case is of steel with solid base. The shrapnel filling is composed of 252 balls, each approximately 167 grains in weight (42 to the pound). The balls are approximately 0.5” in diameter. The balls are poured around a central tube and rest upon a steel diaphragm, the interstices containing a smoke-producing matrix. The bursting charge consisting of 2¾ oz. of black powder is in the base and is covered by the diaphragm which supports the central tube, affording a conduit to the flame leading from the fuze to the bursting charge.

In action the case is not ruptured upon the explosion of the bursting charge; the head is stripped and the balls are shot out of the case with an increase of velocity of about 274 feet per second. The remaining velocity of the shrapnel at 6,500 yards is approximately 724 feet per second and the time of flight 22 seconds, so that at that extreme range, with the increase of velocity due to the bursting charge, this shrapnel with 21-second fuze will be effective. The weight of the shrapnel with fuze is 15 pounds.

Shrapnel is a projectile containing a great number of hardened steel balls, each approximately ½” diameter, which may be projected from a point in the air (called the point of burst) close to but short of the target. Each ball is capable of killing a man or horse at a distance up to 250 or 300 yards from the point of burst. Taken collectively, the paths of these balls form a cone, called the cone of dispersion. The ground section of this cone is elliptical in shape with its longer axis approximately in the plane of fire. At mid-range when burst at normal height of burst (H. B. = 3 mils), the dimensions of this area are approximately 20 yards wide by 250 yards deep. These dimensions will however vary with the angle of fall, the height of burst, the slope of the ground at the target, and the relation between the linear and the rotational velocities of the shrapnel at instant of burst in the air. A 3-mil H. B. is chosen because this gives an average density of 1 hit per square yard of vertical target area. An infantry skirmisher (standing) with his interval occupies approximately 1 square yard.

Shrapnel has very little effect upon material objects. It is very effective against personnel not protected by cover, or to search an area which is known to be occupied, or which must be traversed, by hostile troops.

Ehrhardt High-explosive shrapnel.—The Ehrhardt high-explosive shrapnel is fitted with a combination fuze and a high explosive head. The case is drawn steel with solid base. The shrapnel filling is composed of 285 balls, each approximately 138 grains in weight (50 to the pound). The balls are poured around the central tube and rest upon the steel diaphragm, the interstices containing a matrix of high explosive.

In time action (burst in air), the case is not ruptured upon the explosion of the bursting charge, but the head is forced out and the balls are shot out of the case with an increase of velocity of from 250 to 300 feet per second. In the meantime the head continues its flight, detonating on impact.

If the fuze be set at “safety” or for a time greater than the actual time of flight, this shrapnel may be used in lieu of high-explosive shell. Upon impact a high-explosive shrapnel is detonated by means of the percussion element of the combination fuze, the head being detonated first, which detonation causes the sympathetic detonation of high-explosive matrix surrounding the balls.

Common steel shell.—This steel shell is high-explosive and fitted with a base detonating fuze. The case is hollow and made of drawn steel. It is provided with an ogival head. The steel shell contains a bursting charge of 13.12 ounces of Explosive D. The weight of the shell with bursting charge and fuze is 15 pounds. The shell is always issued filled and fuzed.

This shell bursts on impact and with great force exerted in all directions. It is a powerful instrument for the destruction of material objects such as guns, intrenchments, houses, stone walls, etc. The effect, however, is very local.

Frankford Arsenal combination fuzes.—These fuzes are point fuzes with combination time and percussion elements for use with common shrapnel. They are of the type known as the ring or “dial” fuze, in which the time train is set by turning a graduated ring which carries part of the train. These fuzes may be reset as often as desired.

Ehrhardt combination fuze for high explosive shrapnel.—This fuze is similar to the Frankford Arsenal Combination time and percussion fuze but in addition contains a high explosive head and detonating element. Due to this arrangement, both the projectile and the high explosive head have a high-explosive shell effect when striking on impact.

The service base detonating fuze.—The details of the detonating fuze and the composition of the detonator are kept secret. A detonating fuze is necessary in order to produce a higher order of explosion by causing an instantaneous conversion of the high explosive compound called “Explosive D” with which the shell is charged. If an ordinary percussion fuze were used only an ordinary explosion would be produced as in the explosion of black powder.

Preparation of blank metallic ammunition.—Blank metallic ammunition will always be assembled under the personal supervision of a commissioned officer, who will be held responsible that it is prepared in the manner prescribed. (G. O. 9, War Dept., Jan. 11, 1908.)

For this purpose there are issued blank-cartridge cases, black powder in bulk, tight-fitting felt wads, rubberine, or other quick-drying paint, primers, etc.

Before assembling, the cartridge cases should be carefully inspected to see that they are in sound condition and thoroughly clean and dry. They should also be tested by trying them in the gun, to determine whether they have become deformed. Any cases that do not readily enter the chamber in the gun or that are otherwise seriously deformed should be laid aside for resizing. After inspecting the cartridge cases the blank ammunition should be prepared as follows:

(a) Insert the primers with the primer-inserting press.

(b) Pour into the cartridge case the proper weight of black powder and shake it down well.

(c) Insert the felt wad and press it down hard until it rests squarely on the powder charge.

(d) Give the upper surface of the felt wad and the inside of the cartridge case just above the wad a good coat of the rubberine or other quick-drying paint furnished for the purpose, using a brush, and allow the case to stand until this coat is dry. Then apply another coat of rubberine paint in a similar manner. The object of using rubberine paint, which is strongly adhesive, is to thoroughly seal the joint between the wad and the case to prevent any powder grains from leaking out, and at the same time to firmly hold the wad in place.

The reloading and cleaning outfit.—This outfit consists of the following parts, and is furnished to each battery:

• Primer-inserting press, small
• Bushing
• Powder measure, saluting
• Decapping tool, with guide
• Cleaning brush
• Hammer
• Case holder
• Case-holder stand
• Storage chest

The bushing is used in the primer-inserting press for the insertion of new primers.

The decapping tool and case holder and stand are used for removing exploded primers from the cartridge cases. A light blow on the rod with a piece of wood or the bronze hammer generally removes the primer.

A powder measure to suit the saluting charge for the gun is furnished, and when level full holds the required charge.

The cleaning brush is furnished for cleaning the cartridge cases after they have been used and should be ordered to suit the size of case for which intended.

Care of Cartridge Cases.—As soon after firing as practicable the exploded primers should be removed from the cartridge case by means of the decapping tools furnished with the reloading outfit. The case should then be thoroughly washed in a strong solution of soft soap and soda to remove all powder residue. It should then be thoroughly dried.

If the cartridge cases are carefully cleaned and washed immediately after firing, not only will less labor be required but the life of the cartridge case will be greatly prolonged.

A good solution for washing cartridge cases may be prepared by using ingredients in the following proportions: 1 gallon of water, 2½ ounces of soft soap, 5½ ounces soda. The mixture should be boiled and stirred until the ingredients are entirely dissolved.

In washing cartridge cases this solution should be used hot and in sufficient quantity to completely immerse the cases.

Neither acids nor solutions of acids will be used for cleaning cartridge cases.

Precautions to be Observed with Fixed Ammunition.

(a) Do not unnecessarily expose ammunition to the sun or load it into a warm gun before time for firing; if this is done, erratic shooting will result.

(b) Handle carefully, otherwise cartridges may become deformed and cause jams.

(c) Never use force or any implements on the base of the cartridge in loading.

(d) See that fuzes set at safety or are provided with waterproof brass cover for transport.

(e) Do not fire ammunition which has been under water with the waterproof brass cover removed.

(f) Both service and blank ammunition should never be carried in the battery at the same time. If conditions are such that both may be used in exercises, only one kind should be in the firing battery; the other should be under lock and key outside the firing position.

(g) Misfires and hangfires are of exceedingly rare occurrence. In case of a failure to fire, the firing handle should be pulled again in order to snap the trigger. If this fails to fire, the breech should not be opened until after the expiration of at least one minute, when the round or cartridge should be removed and placed to one side. Defective ammunition, cartridges and primers should be reported.

With Blank Ammunition.

Firing with blank ammunition will be greatly facilitated by a careful observance of the following:

(a) Before firing, a careful examination should be made of the assembled rounds to see that the felt wads have not become displaced or the cartridge cases dented or deformed by careless handling. If the cartridge cases have been properly resized and are clean, no difficulty should be experienced in inserting them in the gun, provided the chamber of the latter is clean. The continued insertion of cartridge cases that are not clean causes an accumulation in the gun chamber which may make the insertion of subsequent rounds difficult or impossible.

(b) In firing blank ammunition the gun chamber will be sponged after each round with a damp sponge, to extinguish sparks and remove powder residue resulting from the previous round, before the insertion of another round.

(c) Care will be taken to see that the sponges are not worn and that they thoroughly fit the chamber. The interval between rounds in firing blank ammunition should be sufficient to allow thorough sponging of the chamber and examination to ascertain that all sparks have been extinguished.

(d) Wads for the preparation of blank metallic ammunition are made to tightly fit in the cartridge case. No wads should be used that are not a tight fit in the case.

FUZES.

Principle of operation.—We have just learned something of the force of inertia in connection with a projectile. Most fuzes are actuated by this force. From our knowledge of the trajectory we know that usually a projectile does not strike on its nose. Therefore we cannot devise our fuzes to work like the driving of a nail into a board. The striking element is the anvil and is a fixed pointed spur against which a sliding element containing a fulminate strikes. The sliding block carries a small charge of black powder which is set off by the fulminate, thus igniting the train which leads to the high explosive charge detonator. Were this sliding block left free to slide back and forth at all times it would be unsafe to transport the fuze, as it might be set off by accident. There must be therefore some means of holding it safely away from the anvil until it is desired to detonate the charge. There are thus two conflicting conditions to be met: safety during transportation and sensitiveness at the point of departure. It may not be understood at first why sensitiveness at the point of departure should be a condition to be met. Suffice it to say that all fuzes are designed to arm at discharge or soon after leaving the bore for they must be ready to act at any time after leaving the muzzle. Were they to be safe during flight they might be so safe that the remaining velocity would not be sufficient to set them off. All fuzes are designed to arm as we say either during travel through the bore or immediately after.

Methods of Arming.

Spring method.—Let us suppose that after our projectile has started on its way the sliding block is free to move within a cavity at the forward end of which is the anvil. If the projectile comes to a sudden drop or even sudden reduction of velocity the block if unrestrained will, according to the principle of inertia, keep on going till something stops it. The something in this case is the anvil and the fulminate cap is set off. But it is not so simple. For while the projectile is in flight it is acted upon by the air resistance and slows down but the block in the cavity of the head is not subjected to this resistance. It therefore gains on the projectile or creeps forward in the cavity unless restrained as it is by a spring. Now one more point and this type of fuze is complete. We supposed that our block was free to slide. For safety’s sake it is pinned to the cavity. Again we call upon inertia to bread the pin so as to leave the block free to slide. The strength of the pin is calculated so that the force of inertia of the mass of the block is greater than the resistance of the safety pin and when the projectile starts the pin breaks and the spring forces the block to the rear of the cavity until the sudden stop of the projectile permits the block to slide forward as explained. Such a fuze requires a comparatively high initial velocity and is not adapted to howitzers using low muzzle velocities.

There are three other methods in use to arm the fuze. They are inertia of a sleeve; centrifugal force and powder pellet system, that is, combustion of a grain of powder holding the sliding block from the anvil by means of an arm resting against the unburned powder grain. These are more sensitive than the type described.

In the first system, a sleeve fitting around the plunger carrying the cap slides to the rear by inertia when the projectile starts and two clips engage in notches on the plunger body making the sleeve and plunger thereafter move as one body, they are thus held together by a plunger spring which before arming held the plunger away from the anvil. The safety spring held the sleeve and plunger away from the anvil and after arming prevents forward creeping by the plunger and sleeve now locked together. Upon striking, the plunger and sleeve move forward as one body and the cap strikes the anvil.

In centrifugal systems the primer plunger is kept safely away from the anvil by a lock which is kept in place by springs. When the rotational velocity reaches a certain point the force of the springs is overcome by the centrifugal force and the locks are thrown aside or opened and the plunger is free to move forward on impact.

In the powder pellet system (the one largely used by the Germans) there is a well or channel filled with compressed powder, this is set off by a fulminate cap which is fired by inertia, a small plunger-anvil striking the cap. When the powder is consumed it leaves a channel into which an arm attached to the sliding block carrying the igniting fulminate for the charge may slide, thus permitting the block to slide forward to the anvil fixed in the forward part of the cavity. It is held from creeping forward after the compressed powder is burned by a safety spring, thus insuring sufficiently hard an impact to set off the cap.

Heretofore in our service the fulminating cap has been fixed and the plunger carried the anvil or as we call it the firing pin. Such is now the system in our base detonating fuzes, and in our combination fuze.

The new point detonating fuzes are patterned after the French and are practically French fuzes.

Fuzes Classification.

Fuses are classified as:

(a) Percussion if it acts on impact, producing a low order of explosion.

(b) Time when it acts in the air at a certain point of the trajectory.

(c) Combination if it is able to act in the air or upon impact.

(d) Detonating when it contains a fulminate which will bring about detonation upon impact.

The detonator may be separate or incorporated in the fuse. For the 75-mm gun and the 155-mm howitzer it forms a part of the fuze.

Many fuzes are armed on set-back. An exception to this is the long detonating fuse, MK 111, which is armed by the unrolling of a brass spiral holding together two half rings made of steel so fitted as to prevent the anvil and the head of the fuse from getting close together. The spiral unrolls when the rotational velocity of the projectile reaches a certain speed, thus drawing away the two steel rings and arming the fuse.

DETONATING FUZE—MARK-III.

DETONATING FUZE—MARK-V.

It is of great importance that the spiral spring be not unrolled during transportation or storage. This is prevented by winding a tape of tarred canvas around the spirals, the head being covered by a thin band of tinfoil. Just before loading the projectile the head and tape are removed by pulling the free end of the tape.

The following precautions concerning fuses must be rigidly observed to prevent grave accidents:

1. All detonators and detonating point fuses must be fitted with a felt washer underneath, thus insuring proper seating in the central tube.

2. Never disassemble a fuse by unscrewing.

3. Any fuse, the parts of which have become accidentally unscrewed, must be destroyed at once. If fired it may cause a premature burst; if handled a grave accident may result.

4. Any fuse or projectile which has been fired is dangerous, because it may then be able to detonate by a very slight shock. It is forbidden to touch it.

5. Never remove the tin hood from the long fuse before having screwed the fuse in the central tube.

6. After having removed the tin hood, be sure that the spiral is in its proper position. Never use a long fuse without the spiral.

7. Be sure the men understand that this spiral must not be removed. It has happened that men have removed this spiral, thinking that it was a device similar to the safety ring in trench mortar fuzes, MK VII E.

8. See that the ring of the long fuze which connects the powder train to the fuze body cannot be unscrewed. If it can be unscrewed the fuze should be sent back to the depot.