a. General

The 15-cm s.I.G. 33¹⁴ is a standard German infantry support weapon found in the cannon company of the infantry regiment (see figs. 80 and 81).¹⁵ It fires a high-explosive shell with a percussion fuze, or a smoke shell, and is used for either high- or low-trajectory shooting. The gun may be horse- or motor-drawn or self-propelled (see fig. 82).

Figure 80.—15-cm infantry howitzer in action.

Figure 81.—15-cm infantry howitzer (rear view).

b. Table of Characteristics

c. How to Operate

(1) Safety.—The safe-and-fire shaft passes from the right face of the breechblock to the firing-pin way. Its right end is formed into a grip, marked with an arrow which may be set to sicher ("safe") or Feuer ("fire"), so marked on the breechblock. At the other end it is reduced to a semicircular section; it is so placed that the flat surface either engages a surface of the firing pin, or, if the shaft is turned through 90 degrees, is cleared by it.

The breechhlock locking plunger passes from the rear face of the breechblock to the safe-and-fire shaft (see figs. 83, 84, and 85). It is held against a surface of the latter by a spring. When the safe-and-fire shaft is set to "safe," the rotation of the shaft forces the locking plunger back against its spring so that it projects beyond the breechblock and engages a recess in the breechblock way, thus locking the breechblock in the closed position.

When the safe-and-fire shaft is set to fire, the locking plunger is enabled, under pressure of its spring, to re-enter the block, which is then free to move.

Figure 82.—15-cm infantry howitzer on self-propelled mount.

(2) To load and fire.—To open the breech, grasp the breech-mechanism lever and press the catch inward. This raises the catch clear of the stop on the breech ring, so that the breech-mechanism lever can be rotated. Then rotate the breech-mechanism lever clockwise through 180 degrees. The rotation of the breech-mechanism lever forces the toe of the crank against the right side of the groove in the top face of the block, thrusting the block to the right into the open position.

Insert a round.

To close the breech, return the breech-mechanism lever to its original position and release the handle, so that the catch is held behind the stop on the breech ring.

Figure 83.—Firing mechanism of 10.5-cm light field howitzer 18 (l.F.H. 18). (This firing mechanism is similar to that of the 15-cm infantry howitzer.)

The rotation of the breech-mechanism lever forces the toe of the crank against the left side of the groove in the top face of the block, thrusting it to the left into the closed position.

As the breech closes, a projection on the toe of the crank comes into position behind the cam of the crank stop so that the block is locked in the closed position.

Figure 84.—Breechblock of 10.5-cm light field howitzer 18 (l.F.H. 18). (This breechblock is similar to that of the 15-cm infantry howitzer.)

To fire the howitzer, pull the firing lanyard to the right rear. This rotates the firing lever on its axis pin so that the angle of the former bears against the head of the firing plunger, forcing it into the block against its spring. The recess in the plunger in which the upper projection of the trigger is engaged turns the latter in a clockwise direction. The toe of the trigger engages the toe of the tripping-piece, which is pivoted on the firing pin, so that both the firing pin and tripping piece are forced back against the firing-pin spring. As the rotation of the trigger continues, its toe clears the toe of the tripping piece, and the spring of the firing pin asserts itself, driving the striker forward on to the primer of the cartridge. The firing lanyard is now released, and the firing plunger, under pressure of its spring, moves to the right. The upper projection of the trigger, being engaged in the recess of the plunger, turns the trigger in a counterclockwise direction. The toe of the trigger, riding on the inside of the tripping piece, forces it to the right so that the heel of the tripping piece forces the inner cover to the rear. At the same time the heel of the trigger, pressing against a projection on the striker body, forces it, too, to the rear. At the end of this movement, the toe of the trigger trips the toe of the tripping piece, which is returned by the firing-pin spring to the normal position, with the firing pin half cocked and withdrawn from the firing-hole bush.

Figure 85.—Breechblock (rear view) of 10.5-cm light field howitzer (l.F.H. 18).

(3) Sight.—The sight consists of (a) the sight and socket; (b) the line-of-sight device and site clinometer; (c) the elevation (range) mechanism; (d) the cross-leveling gear and bubble; (e) the elevation pointer and cradle pointer; (f) the panoramic dial sight (Rbl.F. 16 or Rbl.F. 32).

(4) Gun crew.—The service of the gun is divided among the gun crew as follows:

(a) The chief of section is responsible for seeing that all duties are properly performed, all commands executed, and all safety precautions observed.

(b) The gunner operates the sights.

(c) No. 1 operates the breech.

(d) No. 2 rams the round home.

(e) No. 3 operates the elevating mechanism.

(f) Nos. 4, 5, 6, and 7 handle the ammunition.

d. Ammunition

(1) General.—The following two types of high explosive shells are used in this infantry howitzer: (a) 15-cm Igr. 38 and (b) 15-cm Igr. 33. There is also a smoke shell.

The only point of difference between these two types is that the Igr. 33 has a screwed-in baseplate, whereas the baseplate of the Igr. 38 is in one piece with the shell body. The high-explosive capacity is large (21.8 percent). The Igr. 33 is obsolescent, and no more ammunition of this type will be issued when present stocks are exhausted.

(2) 15-cm Igr. 38 and 15-cm Igr. 33 (HE shell).—(a) Projectile.—

(b) Fuze.—The fuze s.Igr.Z. 23 is a highly sensitive, nose-percussion fuze with an optional delay of .4 second. It operates on impact or graze.

(c) Cartridge.—The rimmed brass cartridge case, with a c 12 n/A percussion primer, has the following dimensions:

The markings s F H 13 suggests that the cartridges for the 15-cm s.Inf.G. 33 and the 15-cm s.F.H. 13 are interchangeable.

The cartridge case is closed at the top by a cardboard closing cap.

The propellant consists of six removable parts so that the shell may be fired with any one of six charges. Charge 1 consists of Part 1; charge 2 of Parts 1 and 2; charge 3 of Parts 1, 2, and 3, etc.

Each part is contained in a silk bag on which the details of the weight and type of propellant are stencilled, as follows:

(3) 15-cm Igr. 38. Nebel (smoke shell).—This smoke shell may be identified by the white letters "Nb" on a field-gray projectile which weighs 38.50 kg (85 pounds). The bursting charge consists of picric acid, and the exploder system comprises a detonator set in penthrite wax enclosed in an aluminium container. The shell produces a smoke cloud 50 meters (55 yards) thick.

e. Maintenance

(1) General.—Because of the complexity of the mechanism and because of the lack of definite authoritative information on this weapon, the description under the heading of maintenance cannot be made complete.

(2) To disassemble breech mechanism.—The breech mechanism may be removed in the following order: (a) set the safety-catch to Feuer ("fire"); (b) by means of breech-mechanism lever, open the breech mechanism until the extractor bolt is clear; (c) hold the firing lever in the "fire" position and remove the extractor bolt; allow the firing lever to return to its normal position and remove the extractor; (d) crank the breechblock clear of the cam and withdraw; (e) remove the breech-mechanism lever by aligning the key with the keyway and lifting.

f. Carriage

(1) General.—The carriage is of the box type. It is fitted with a fixed spade and is also provided with an attachable sand spade. Toward the front are the trunnion bearings which receive the trunnions of the cradle, and there is a spring compensator on each side piece. The elevating handwheel is mounted on the right of the carriage, and the traversing handwheel on the left. A shield is fitted at the front, and a box for spares at the rear.

When traveling, the cradle is secured by a clamp to the carriage, to the center of which the sand spade is also secured.

(2) Cradle.—The cradle is trough-shaped and is provided with guide ways, in which guides on the gun move as it recoils and runs out. On either side at the front is a pad to receive the unabsorbed force of run-out, and between them is the expansion chamber which receives the buffer fluid forced from the buffer by expansion as it becomes heated. Towards the rear are the two cradle arms to which the trunnions are fixed. Each trunnion is provided with a cranked compensator lever which compresses the compensator spring. The elevating arc is secured underneath, and the recoil indicator at the right rear. The clamp is at the front of the carriage, and is operated by a lever secured to the clamp shaft.

(3) Elevating gear.—The elevating gear is operated from the right of the carriage. It consists of a worm gearing, rack, pinion, and shafting.

(4) Traversing gear.—The traversing gear is operated from the left by a system of gear wheels and shafting.

(5) Spring compensators.—The spring compensators are fitted longitudinally, one on each side of the carriage. They neutralize muzzle preponderance at all angles of elevation.

¹⁴ Schweres Infanteriegeschütz 33 (see p. 136, note 10, above). The German tactical symbol for the heavy infantry howitzer is or .
¹⁵ See fig. 1, P. xii, above.
¹⁶ 149.1 mm equals 5.87 inches.
¹⁷ 11 calibers.
¹⁸ One turn of elevating handwheel equals 12 mils.
¹⁹ One turn of traversing handwheel equals 2.2 mils.