United States. Army. Ordnance Dept.

Handbook of artillery : including mobile, anti-aircraft and trench matériel online

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Online LibraryUnited States. Army. Ordnance DeptHandbook of artillery : including mobile, anti-aircraft and trench matériel → online text (page 6 of 19)
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There will soon be issued to the service a number of model 1916
75-millimeter gun carriages, redesigned to mount a St. Chamoiid
hydropneumatic recoil mechanism in place of the hydrospring type,
and a standard 75-millimeter gun modified and fitted with a counter-
weight. The new materiel will be known as the 75-millimeter gun
materiel, model of 1916 ML

The St. Chamond recoil mechanism as adopted for these carriages
was developed during the war in 1917 by Col. Rimailho, of the French
Army. This mechanism, of the hydropneumatic type, is durable and
smooth in operation. The use of small cradle forgings was made
possible by the introduction of high pressures in the recuperator and
recoil cylinders. In order to hold these pressures, it was necessary
to develop suitable packing, and the success of this recoil system is
largely due to the design of these packings.

The St. Chamond recoil mechanism consists of three cylinders, the
middle one being the recoil cylinder, the right cylinder having an air
reservoir at its forward end, and an oil reservoir at its rear end; the
left cylinder, known as the recuperator cylinder, has at its forward
end an air space, and at its rear end a floating piston and regulator
for controlling the length of recoil.

The recoiling parts are held in battery by the reaction of the air on
the floating piston transmitted through the liquid against a leak-
tight recoil piston. In recoil the gun moves to the rear, carrying with
it the recoil piston (middle cylinder) . The energy of recoil is absorbed
by the throttling of the oil through a spring-controlled orifice in the
regulator valve.

An opening is provided between the recoil and the recuperator
cylinders to house the regulator valve. During recoil, the pressure in
the recoil cylinder opens the regulator valve, the movement of which
is controlled by a helical spring and Belleville springs. The oil pass-
ing through the orifice controlled by this valve moves the floating
piston forward against the air pressure, thereby storing up energy to
return the gun from the recoiled position to its position in battery.
The valve in the counterrecoil orifice remains closed during recoil.

The throttling during recoil is controlled by the regulator valve ?
which consists of two parts, an upper stem and a lower valve stem.
The lower valve stem is seated on a circular seat at the entrance
channel to the valve. As the valve lifts, the throttling area becomes



the Vertical circumferential area between the valve and its seat. In
long recoil the movement of the valve is controlled by a spiral spring
which reacts on the lower valve stem. The upper stem rests in a valve
housing and has Belleville springs reacting on the stem only. To
move the upper valve stem, the whole housing is lowered automatic-
ally by a cam operated by the elevation of the cradle. At short recoil,
the upper stem of the regulator is brought down by the cam until its
lower surface is in contact with the top surface of the lower valve
stem in order to control the throttling of the valve.

The regulator valve is closed during the counterrecoil movement.
The oil flow during counterrecoil is different from that during recoil,
the counterrecoil flow path being through a small channel beginning
at the inside end of the buffer chamber in the recuperator cylinder
and finally emptying into the recoil cylinder. The throttling during
counterrecoil takes place through a constant orifice located at the
beginning of the counterrecoil channel. The tapering buffer rod on
the floating piston in the recuperator causes additional throttling
through the small annular area between the buffer chamber and buffer
rod of the floating piston, which brings the recoiling parts to rest
without shock.

18322820- 6



The -French 75-millimeter field gun adopted for the service of the
United States dates back to 1897, when it was perfected by the
French Army.

The French model 1897 field gun has fired, on test, as high as 30
shots in a minute, and it is understood that the American model
1916 equaled this rate; likewise, a St. Chamond gun with interrupted
screw-type breech on the special St. Chamond recuperator. Apart
from the personnel service to the piece, the length of time which either
gun could maintain this rate of fire, or any other rapid rate of fire,
is perhaps not definitely determined. As to whether or not such
length of time would be limited by the heating of the gun or by the
heating of the recoil mechanism is likewise perhaps not definitely

Rapidity of firing is of vital importance, for it is self-evident that
under certain conditions a gun which can fire twice as many shots
per minute as some other gun is, for the moment, equivalent to two
guns of the second class. Rapidity of firing action is dependent
upon the arrangements involved for the sighting, maintaining of the
gun on its range, loading, firing, time of recoil and return of the gun
to battery position, opening of the breech, and ejection of the empty
cartridge case.

For artillery of position a great part of the enormous energy re-
quired to start the projectile on its way may be absorbed by a heavy
foundation furnished as a mounting for the piece. An efficient recoil
mechanism is, however, of vital importance in connection with light
artillery for field service, owing to the essentially light weight of the
carriage on which the gun is mounted, to permit of its ready mobility.

The recoil mechanism not only absorbs the greater part of the
recoil energy of the gun, but it returns the gun to the battery or fir-
ing position, and to be efficient it must be able to perform these two
functions quickly, smoothly, surely, and continuously. The word
" surely" is used in the sense of firmly and without shock, and of
being reliable. The recoil mechanism not only takes up the recoil
but it forces the gun all the way back into battery, or to a position
within the variation which the design permits, under all conditions
of elevation and heating.

The general theory of hydropneumatic recoil mechanism is not
new. In its relation to light artillery its most notable exemplifica-
tion in battle has appeared in the Puteaux Arsenal type of the French
piece. Its virtues have been widely heralded and every effort has
been made to keep its construction secret. Its several parts were





manufactured at different points in France and these were assem-
bled in a small room at the Puteaux Arsenal, and but few persons
were admitted to this room. In the agreement, to manufacture of
the complete recuperator in the United States, it was stipulated that
the greatest secrecy should be maintained with reference to its de-
sign, manufacture, and assembly.

There is a difference between land and naval warfare, in this
respect: In a duel between two large fighting ships of equal speed
to insure their remaining in contact, the one with the heavy, long-
range guns has the other at its mercy, as it can destroy both its oppo-
nent's base and at the same time its opponent's personnel by sinking
the opponent ship. In a land battle, the fortifications may be re-
duced by the long-range gun, of heavy caliber, but it is the destruc-
tion or capture of personnel which brings a war to an issue and the
personnel may move to open country and open order, under which
conditions the heavy, long-range gun, which is expensive to construct,
slow and difficult to transport, expensive to fire, and withal short of
life, no longer has a great target on which its tremendous energy may
be concentrated.

Land warfare has clearly demonstrated that it is the killing and
disabling of personnel or the capture of enemy troops in large num-
bers which far outweighs the capture of cities or of terrain which
is nonproductive of raw material, in the forcing of an issue. This
75-millimeter gun was most effective in the open-country fighting, in
the protection of troops and in working havoc among enemy troops
and bringing in prisoners by creeping barrage laid behind an enemy

Weights, dimensions, and ballistics.

Caliber millimeters. . 75

Total weight of gun and breech mechanism pounds.. 1,015

Total length of gun inches.. 107. 125

Rifling, uniform, right hand, 1 turn in 25.6 calibers.
Muzzle velocity:

Shell (short fuze) feet per second. . 1, 955

Shell (long fuze) do 1, 930

Shrapnel do. ... 1, 755

Maximum range:

Shell (short fuze) (Mark IV shell) yards. . 8, 640

Shell (long fuze) do 9, 350

Shrapnel do 7,440

Weight of complete round of ammunition:

Shrapnel ; pounds. . 16

Shell .do .... 12. 3

Diameter of steel tired wheels inches. . 52. 5

Width of track do 59. 68

Length of recoil of gun on carriage do .... 44. 9

Height of axis of gun from ground do 40. 4

Maximum angle of elevation degrees. . 19

Maximum angle of depression do 10

Total traverse of carriage on axle do ... 6

Weight of the carriage, complete (without gun) pounds. . 1, 642

Weight of gun and carriage, fully equipped do. . 2, 657





The gun is of the built-up construction type, consisting mainly of
a steel tube reinforced at the breech end with a breech hoop and
covered in the central portion with a bronze jacket. The total
length from face of breech to muzzle is slightly less than nine feet.

The recoil lug under the breech carries the coupling key, which
connects the gun to the recoil mechanism. A safety pin operates
between the breechblock and the coupling key, so that it is impossible
to close the breech and fire the gun when it is not securely locked
to the recoil mechanism of the carriage.

On the underside of the gun are inclined bronze slides which are
in contact with similar slides on the recoil mechanism. Rollers
are also attached to the gun, and during recoil the gun first slides on
the inclined guides and then the rollers lift the weight off the slides,
the remainder of the travel being on the rollers. A pair of rollers
at the muzzle permit a long recoil with short guides by taking the
overhanging weight when the gun is at full recoil.

The 'breechblock is of the Nordenfeld type, cylindrical in shape and
threaded on the outside. It is opened or closed by the operating
handle from the right side of the gun by the same man who sets the
gun for range and fires the piece. Opening the breech' automatically
actuates the extractor, which in turn ejects the empty cartridge case.
The round of ammunition is fired by a striker which is driven for-
ward by a spring-actuated hammer pulled by the lanyard.

The carriage is very compact and simple, consisting of a housing
around the axle, above which is the support for the cradle, and a
box section trail ending with the customary spade and lunette
Seats are provided for two men, the one sitting on the right side
operating the range scale mechanism, opening or closing the breech
and firing the piece; the man on the left sighting the gun and oper-
ating the angle of site and traversing mechanisms.

The reccil mechanism is of the hydropneumatic, long recoil type
and contains both recoil and counterrecoil mechanisms. A gage
plunger is located in the rear end of the cradle which, when flush,
indicates that more oil should be added until the plunger projects
about f inch. Oil may be added by forcing it through a valve in the
side of the cradle by a hand screw filler, or by means of a portable
battery pump clamped to the side of the trail and connected through
the trunnions to the interior of the cradle.

The recoil mechanism is housed inside of the cradle, through which
are bored an upper and lower cylinder, filled with Oleonapthe, able
to communicate together by means of a passage provided for that
purpose. The front part of the upper cylinder (in front of the
piston) is permitted to communicate freely with the air through a







plug, but the forward end of the lower cylinder is closed and con-
tains compressed air at approximately 150 kilograms per square
centimeter (1,833.5 pounds per square inch).

In the upper cylinder a piston is permitted to move, the piston
rod, however, being secured to the gun. The lower cylinder is
fitted with a pipe, at the end of which is a circular ring, this pipe
being screwed in the rear part of the cylinder where the valves are
housed. A diaphragm equipped with a hollow rod, also a floating
piston fitted with a small rod, a/re incorporated in the low r er cylinder.

During recoil the piston of the upper cylinder compresses the
liquid, forcing it to pass through various valves, also openings
formed between the pipe and the hollow rod of the diaphragm. The
passing of the liquid through these different openings constitutes the


braking, in so moving, the liquid opens the valves (which are widely
opened at the beginning of the recoil and gradually close in propor-
tion to the decrease of the speed of the recoil). At the same time,
the air in the lower cylinder is compressed by the action of the
liquid on the diaphragm. To return to battery at the end of the
recoil, the compressed air forces the diaphragm back. The liquid
thus compressed acts directly on ,the upper cylinder piston, causing
it to return to its initial position.

The interior of the recoil mechanism was maintained confidential
by the French Government before and during the war, and when its
manufacture was taken over by the Ordnance Department, agree-
ment was made to continue the secrecy of these parts. Very fine
adjustments are made when the parts are assembled, and conse-
quently no repairs or adjustments are permitted to be made in the
field. The complete recoil mechanism must be sent to special


repair depots. The recoil mechanism will function properly without
the operating personnel understanding the interior mechanism.

The angle of site mechanism consists of a handwheel and gears,
and provides for elevating or depressing a rocker 13 degrees with
reference to the trail. The rocker fits around the trunnions and
has a segment of a gear which meshes with the elevating pinion.
To the rocker is secured an elevating screw and nut which connects
with the cradle. In setting the angle of site, the rocker is set in
motion, thereby moving the cradle and gun.

The range scale mechanism which operates the elevating screw
provides an elevation of 12 degrees to give the correct range and is
obtained by movement of the cradle in reference to the rocker.

The circular scale graduated in meters indicating the range, is
mounted on the side of the cradle and through gearing is connected
to the elevating screw. A range rack is connected to the rocker
arm which is also graduated in meters. On carriages made in
America an extra strip is placed alongside the range rack and is
graduated in mils. The range scales are graduated up to 5,500
meters, but greater ranges can be obtained by burying the trail,
and thus giving higher angles of elevation. Interference of the
breech against the trail, however, limits the total possible elevation
obtainable by combination of the elevation due to the angle of site
and due to range to 19 degrees.

On this carriage axle traverse is used. A geared nut, held inside
of the axle housing, rotates around the axle which is threaded with
a coarse rectangular thread. Movement of this nut forces the
carriage to the right or left, pivoting around the spade, one wheel
advancing and the other backing up. Traverse is about three
degrees right and three degrees left.

A combination road brake and firing support is hung around the
axle, permitting the application of brake shoes against the tires
of the wheels when traveling, and the lowering of the framework to
the ground and mounting the wheels thereon, for firing. This last
operation is called abatage, the three steps being indicated in the
following figures:



Wooden wheels, 1,334 millimeters (52.5 inches) diameter, are used,
and have steel tires 3.5 inches wide. These wheels are interchange-
able with the French limber wheels, but not with the American
limber or caissons for the 75-millimeter gun carriages.




The customary shield and apron protects the gunners when
under fire.

The angle of site mechanism is also called the independent line
of sight, because the range setting is independent of the setting of
the angle of sight, which is done by the angle of sight handwheel.
% The sight, model of 1901 (French), includes the collimating sight,
angle of site level, and angle of site scale. It is mounted on the
left side of the rocker, at the trunnions. It has no telescopic features
and, therefore, its range is limited. An auxiliary angle of site level
is furnished to replace the regular level and gives an additional 200
mils for use in the hilly or mountainous country.

Fixed ammunition is used in this 75-millimeter field gun and is
made up with either common shrapnel or common steel shell.
Shrapnel rounds are issued with the projectiles filled and fuzed; the
shell rounds are issued filled but not fuzed, and contain an adapter
with booster charge.

The projectiles average in weight: Shrapnel, 16 pounds, fuzed;
shell, 12.3 pounds, fuzed. The components of one round are the
cartridge case, with primer; the powder charge; projectile; and fuze,
in shrapnel; and adapter and booster in the shell.


A battery of 75-millimeter gun carriages, model ol 1897M1 (French)
is accompanied by the following vehicles:

75-millimeter gun and carriage, model of 1897M1.

75-millimeter gun carriage limber, model of 1918.

75-millimeter gun caisson, model of 1918.

75-millimeter gun caisson limber, model of 1918.

Battery and store wagon, model ol 1917.

Forge limber, model of 1902M1.

Store limber,. model of 1902M.1.

Battery reel, model of 1917. 1

Reel, model of 1909M1. 1

Cart, model of 1918. 1

The gun and carriage are of the French design, and of both French
and American manufacture. The accompanying vehicles are all of
American design and manufacture.

1 For horse batteries the battery reel, model of 1917, is issued. For motorized batteries, the reel, model
of 1909 Ml, with the cart, model of 1918, is issued in lieu of the battery reel, model of 1917.



The 75-millimeter gun, model of 1917 (British), was originally
known as the 18-pounder, but was modified by adapting it to the
75-millimeter caliber materiel. This weapon is equipped with cus-
tomary unit trail; the interference of the trail with the breech limits
the gun elevation. With the split trail, the breech can pass down
into the V formed by separating the two sections of the trail. The
theoretical elevation for obtaining maximum range under ideal bal-
listic conditions is 45 from the horizontal, and is actuallv some few


degrees less than this. Increased range is sometimes obtained with
field guns whose normal elevation is limited by setting the axles or
wheels on raised surfaces, or by sinking the trail below the level of
the wheels, for the purpose of pointing the gun at an elevation higher
than the mechanical arrangement of the carriage permits. This is,
however, a subterfuge, limited in its practical application.

The American model 1916 split-trail carriage permits great eleva-
tion within the mechanism of the carriage and likewise a wide
traverse without changing the position of the trail. The recoil
mechanism on the 1916 model was adapted to the higher permissible
elevation of the gun, and was supplied with a variable recoil, auto-
matically adjusted to different elevations. The ability to outrange


18322820 7



the enemy is an attainment constantly being sought, and therefore
high elevation and reduction of resistance of the projectile passing
through air are the means through which it was hoped to obtain the
increased range desired. Likewise, a wide horizontal arc of fire,
without resetting of the trail and consequent resetting of the sight-
ing devices, is a great convenience and saver of time.

As compared with the British model 1917, the American 3-inch
model of 1902 carriage permits of a maximum angle of elevation of
15, depression of 5, and traverse of 142 mils, while the British
model permits 16 elevation, 5 depression, and 142 mils traverse.
The French model 1897 carriage permits a maximum angle of eleva-


tion of 19, depression 10, and traverse 106 mils. The American
model 1916 carriage allows a total vertical movement of from 53
elevation to 7 depression, and a traverse of 800 mils (an artillery
mil equals the angle of - 6 -4W f a circumference). The American
model 1902 carriages are arranged with an hydro-spring recoil mech-
anism, and so is the British model 1917 and the American model
1916. The French model 1897 carriage is equipped with an hydro-
pneumatic recoil mechanism.

The basic difference of the recuperator or recoil mechanism of the
French model 1897 gun, as compared with the British model and the
American model, lies in the fact that the French model involved the
principle of oil and compressed air for absorbing the recoil of the gun


and returning it to battery or firing position, and is practically self-
contained in one large heat-treated steel forging, with a system of
finely fitted surfaces and adjustment valves. In the British and
American model recoil mechanism, oil and steel springs, instead of
compressed air, are employed, with a combination of pistons and
steel tubing.

A reference may also be made relative to the desirability of single
or unit trails as compared with the split trail. The latter allows of
greater traverse, but as a new objective makes necessary a resetting
of the trail, the change in setting requires much more time than with
the unit trail. The split trail is heavier and the equalizing mecha-
nism, necessary to the proper distribution of recoil shock to both trail
sections, establishes a relative movement between the two trail sec-
tions, with the result that the split trail can be set up less quickly
than the unit trail on uneven ground.

Weights, dimensions, and ballistics.

Caliber millimeters. . 75

Weight of gun and breech mechanism pounds. . 995

Total length of gun inches. . 88. 21

Length of bore do. ... 83. 915

Rifling, right-hand twist, zero turns at origin to 1 turn in 75 inches at 9.72
inches from muzzle, thence uniform.

Number of grooves 24

Muzzle velocity:

Shrapnel feet per second. . 1, 693

Shell (short fuse) do. ... 1, 900

Shell (long fuse) do. ... 1, 876

Maximum range:

Shrapnel (Mark IV shell) yards. . 6, 464

Shell (short fuse) do.... 8,100

Shell (long fuse) do. ... 7, 450

Weight of one round of ammunition:

Shrapnel pounds. . 16

Shell do. ... 12. 3

Weight of carriage, complete f without gun) do 1. ; .*>

Weight of gun and carriage, fully equipped do 2, 945

Weight of gun and carriage in battery position do 2, 860

Diameter of wheels inches . . 56

Width of track do .... 60

Length of recoil of gun on carriage do 49

Height of axis from ground do 38. 86

Maximum angle of elevation degrees . . 16

Maximum angle of depression do 5

Maximum traverse, each side of center mils . . 72

1 2 3 4 6 8 9 10 11 12 13 14 15 16 17 18 19

Online LibraryUnited States. Army. Ordnance DeptHandbook of artillery : including mobile, anti-aircraft and trench matériel → online text (page 6 of 19)