The Germans introduced the 7.5-cm l.I.G. 1810 in
Figure 71.—7.5-cm infantry howitzer in action.
(1) General.—The howitzer is drawn by six horses or by a motor vehicle. This weapon can be split into six loads (a maximum of 165 pounds each) for pack transport.
(2) Table of characteristics.—
|Muzzle velocity (maximum)||_ _ _ _ _ _ _||730 feet per second.|
|Maximum range||_ _ _ _ _ _ _||3,870 yards.|
|Theoretical rate of fire||_ _ _ _ _ _ _||15 to 20 rounds per minute.|
|Length of barrel||_ _ _ _ _ _ _||10 calibers (10 x 7.5 cm).|
|Depression||_ _ _ _ _ _ _||177 mils (10 degrees).|
|Elevation||_ _ _ _ _ _ _||1,292 mils (73 degrees).|
|Traverse||_ _ _ _ _ _ _||212 mils (12 degrees).|
|Weight in action||_ _ _ _ _ _ _||880 pounds.|
c. How to Operate
(1) Safety.—The gun cannot be fired until the barrel is properly closed. A projection on the firing lever must enter a recess in the breech-mechanism lever when fully closed (figs. 72 and 73).
The breech-mechanism lever and firing lever cannot be moved when the arrow on the safe and fire lever is at sicher ("safe") because (a) the toe on the breech-mechanism lever engages the safe-and-fire lever and prevents any movement, and (b) the toe on the safe-and-fire lever engages a cutaway portion in the firing lever and prevents any movement (fig. 74).
Figure 72.—Breech of 7.5-cm infantry howitzer.
Figure 73.—Breechblock and firing mechanism of 7.5-cm infantry howitzer.
(2) To load and fire.—To open the breech, set the arrow on the safe-and-fire lever to Feuer ("fire"). Then disengage the retaining catch by gripping the breech-mechanism lever handle, and pull the breech-mechanism lever to the rear. This movement causes the actuating link to be revolved in the slipper block. The inner stud of the actuating link, being displaced from the bearing center of the link, is given a circular motion, causing the slide to be raised and drawn slightly to the rear. The slide, dovetailed to the breech ring, causes the barrel to be revolved about its trunnions and the breech end to be raised to the open position.
When the round is inserted, the extractor is carried forward, the breech-mechanism lever is rotated, and the actuating link causes the slide to move down and forward in its groove, thus lowering the breech to the closed position.
To fire, pull the firing lever to the rear. On rotating the firing lever to the rear, the torsion spring is put under tension. The spring-loaded lug on the shaft engages the firing pin, forcing it to the rear against its spring and cocking it. When the lug on the shaft trips the lug on the firing pin, the latter is allowed to move forward and fire the gun.
The firing pin can be recocked and fired by pulling the firing lever to the rear.
Figure 74.—Firing mechanism parts of 7.5-cm infantry howitzer.
Figure 75.—7.5-cm infantry howitzer in traveling position.
(3) Sights.—The sighting mechanism works on the reciprocating principle (see figs. 76 and 77). It is fitted with a range drum graduated to 1,320 meters and a correction scale for the five charges used. A rocking platform for the sight is operated by a worm spindle and deflection nut. A clicker arrangement is also incorporated.
The dial sight is the Rundblickfernrohr 16 (Rbl.F. 16) (fig. 79).13 The Rbl.F. 16 has a magnification of four and a 10-degree (177-mil) field of view. The graticule shows an inverted V and a broken verticle line. There is no means of focusing the eyepiece, and the gunner must keep his eye about three-fourths of an inch away. There is provision for illuminating the graticule at night.
Figure 76.—Sighting mechanism (side view) of 7.5-cm infantry howitzer.
For a zero angle of site, the upper prism micrometer head is adjusted to a setting of 300 mils.
The azimuth scales are graduated from 0 to 6,400 mils, the main scale being numbered every hundredth mil from 0 to 64 and the micrometer scale every mil from 0 to 100.
Figure 77.—Sighting mechanism of 7.5-cm infantry howitzer, showing range-scale drum.
Separate ammunition is used; the cartridge cases are either 6341 (brass) or 6341 St (steel). Ammunition is carried in baskets holding three rounds, or in a more recent type of metal container also holding three rounds. The following types of shell are used:
(1) HE shell 7.5-cm Igr. 18, with fuze Az. 23 n.A. The weight is 12 pounds 2 ounces. The fuze can be set to instantaneous (o.V.), or to a .15-second delay (m.V.). This shell is not provided for the 7.5-cm l.Geb.I.G. 18.
(2) HE shell 7.5-cm Igr. 18Al., with fuze Az. 23 n.A. The weight is 12 pounds 2 ounces. When fired by l.Geb.I.G. 18, a time and percussion fuze, the Dopp. Z. (S/60) Geb., can also be used. The letters Al are understood to indicate inclusion of a granular, aluminium flash composition in the filling.
(3) Hollow-charge shell 7.5-cm Igr. 38, with fuze Az. 38. It
is fired with Charge V. This shell has been introduced primarily for antitank
purposes, but in emergency it can also be used against personnel. Penetration is
approximately 55 mm at normal, 45 mm at 30°. There are also two practice
Figure 78.—Manhandling 7.5-cm infantry howitzer.
(1) Stripping.—(a) To dismantle breech mechanism.—Turn the safe-and-fire lever to Feuer ("fire"). Remove the firing-pin cover by pushing in and rotating through 90 degrees in a counterclockwise direction. Take out the spring and firing pin. Release the firing-lever retaining plunger by depressing and rotating the lever, and remove the firing lever with the torsion spring and collar. Depress the retaining plunger of the safe-and-fire lever and remove the latter. Hold the breech open and remove the extractor, together with the extractor retainjng catches. After taking out the taper pin, rotate the breech-mechanism lever to the fully open position and remove. Operate the actuating shaft until it disengages the actuating slide, which can then be removed. If necessary, the barrel can now be lifted out.
(b) Recoil and recuperator system.—The recoil system is carried in the cradle, the recoil cylinder on the left and the hydropneumatic recuperator on the right. The hydropneumatic cylinder is placed above the liquid cylinder. A communicating channel connects the cylinders and a valve is fitted to regulate the flow. The liquid cylinder has a piston and packing, and the rear end of the piston rod is secured to the brechblock lug. A spring-loaded valve is fitted to the front of the hydropneumatic cylinder. The recoil cylinder, with piston control rod with sliding valve, is closed by a stuffing box and gland at the front. The rear end has a nut to secure the cylinder to the breechblock lug.
(2) Assembly.—Assemble the breech mechanism by first placing the actuating slide in its groove in the barrel; then insert the actuating link in the slipper and engage it with the slide. Replace the breech-mechanism lever and taper pin. Open the barrel until the extractor and the extractor retaining catches can be placed in position. Insert the safe-and-fire plunger, and spring; pass the safe-and-fire shaft in from the right side, when it will engage and retain the extractor retaining catches. Replace the firing shaft with the two feathers engaging the feather ways in the recess, the smaller feather uppermost. Place a slight tension on the spring and push the shaft home. Insert the retaining plunger and spring of the cocking-and-firing shaft. Finally, replace the firing pin, spring, and cover.
Figure 79.—Panoramic sight (Rundblickfernrohr 16, Rbl.F. 16) used on 7.5-cm infantry howitzer.
The carriage is of the box type, supported on pneumatic tires. It consists of two side pieces supported by transoms at the front. Toward the front, it is prepared with bearings to receive the trunnions on the cradle. The rear end is fitted with a spade, a lunette, and lifting handles. Two boxes for spares are fitted, one in the center and the other at the rear.
(1) Cradle.—The cradle is trough-shaped and fitted with a cover plate. It is formed with trunnions which fit the trunnion bearings on the carriage; at the front, brackets with spring-loaded plungers are fitted for the reception of an upper shield. The elevating arc is secured to the under side, and the recoil indicator to the right side.
(2) Axle.—The axle slides in bearings. Brackets are fitted to the ends, in which the wheel suspension springs and locking plungers are housed. When in the firing position, the locking plungers engage in the wheel cranks.
(3) Elevating gear.—The elevating gear, consisting of a worm gearing, rack, pinion, and shaft, is on the right. The elevating pinion is housed on a shaft between the side plates of the carriage.
(4) Traversing gear.—The traversing gear is operated from the left side and consists of a system of gear wheels and shafts. The carriage is traversed along the axle by means of a traversing nut and screw, fitted to the right side of the axle. The traversing clamp, securing the cradle to the carriage when traveling, is fitted to the left side of the carriage.
(5) Sight bracket.—The sight bracket is fitted to the left side of the carriage. The lower end of its connecting rod is secured to the left cradle trunnion, and the upper end to the sight reader.
10 Leichtes Infanteriegeschütz is translated literally as "light infantry weapon." Sometimes Geschütz is translated as "gun." But this weapon in U.S. terminology is termed a howitzer.
11 See fig. 1. p. xii, above.
12 The German tactical symbol for the mountain-infantry howitzer is .
13 A more modern sight, the Rundblickfernrohr 32 (Rbl.F. 32), is used on the newest equipment.