THE 155 HOWITZER, MODEL 1918
THE HOWITZER.
Weights and Dimensions.
Material Alloy steel.
Weight (including breech mechanism) 1,248 kg.—2,745 lbs.
Caliber 155-mm.—6.1 inch.
Total length 2,332-mm.—91.8 inch.
Length of bore 2,177-mm.—85.7 inch.
Length of rifled portion of bore 737-mm.—68.4 inch.
Rifling
Number of grooves 48.
Width of grooves 7.145-mm.—0.2813 inch.
Depth of grooves 1-mm.—0.03937 inch.
Width of lands 3-mm.—0.1181 inch.
Twist, right hand, uniform,
one turn in 25.586 cal.
Powder chamber:
Diameter 158.75-mm.—6.25 inch.
Length 339.85-mm.—13.38 inch.
Volume 6,965.75 cu. in.—425 cu. in.
Obturation Pad.
Firing mechanism Percussion.
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.
[Illustration: _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.
[Illustration: _155 M.M. HOWITZER MODEL OF 1918_ (_SCHNEIDER_)
_BREECH MECHANISM ASSEMBLY_]
[Illustration: _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.
[Illustration: _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.
[Illustration: 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.
[Illustration: 155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
LEFT SIDE ELEVATION, IN BATTERY]
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 155 MM HOWITZER, MODEL OF 1918 (SCHNEIDER)
AIR AND LIQUID PUMPS]
[Illustration: 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.
[Illustration: _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.