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TM-E 30-480: Handbook on Japanese Military Forces
Technical Manual, U.S. War Department, October 1, 1944
[DISCLAIMER: The following text and illustrations are taken from a WWII U.S. War Department Technical Manual. As with all wartime manuals, the text may be incomplete or inaccurate. No attempt has been made to update or correct the contents of the original technical manual. Any views or opinions expressed do not necessarily represent those of the website.]

Chapter IX: Weapons

Section II: Infantry Weapons

3. MORTARS AND GRENADE DISCHARGERS. a. General. Although all known types of both mortars and grenade dischargers are dealt with here, there are indications that the Japanese Army has mortars heavier than 90-mm and at least up to 150-mm.

b. Model 10 (1921) 50-mm grenade discharger. (1) General description. This is a smooth-bore, muzzle-loaded weapon (fig. 184). It has the special feature of a range control device in the form of a graduated thimble by which a gas port at the base of the tube can be varied in size. For shorter ranges, part of the propellant gases escape to the side. It is believed that this weapon is used primarily for discharging flares and that the heavier model 89 grenade discharger is used for firing high explosive and other projectiles.

[Figure 184. Model 10 (1921) 50-mm grenade discharger (at bottom is the discharger prepared for carrying).]
Figure 184. Model 10 (1921) 50-mm grenade discharger (at bottom is the discharger prepared for carrying).

(2) Characteristics.

Caliber       50-mm (1.97 inch).
Length of barrel9 1/2 inches.
Over-all length20 inches.
Weight5 1/2 pounds.
Range for M91 (grenade)65-175 yards.

(3) Operation. There is no safety device on this weapon. To operate, first remove the safety pin from projectile. The grenade or signal projectile is placed in the barrel. The weapon is fired by a trigger attached to the pedestal.

(4) Ammunition. This weapon fires Model 91 grenade, Model 11 smoke shell, Model 10 flare shell, Model 10 signal shell, Model 91 pyrotechnic grenade and Model 10 blank.

c. Model 89 (1929) 50-mm grenade discharger. (1) General description. This is a muzzle-fed, rifled weapon which is widely used in the Japanese Army (fig. 185). The standard projectile is a high explosive shell which contains the propellant charge in its base. Ranges are controlled by rotation of the knurled range knob. Rotation of the projectile is obtained because the rotating band is expanded against the rifling when the weapon is fired. The weapon is trigger fired. A recent modification of the discharger is fitted with a device to indicate the correct firing angle (45°). There are two range scales. One gives the ranges (120 to 670 meters) governing the use of the Model 89 HE shell and the other (50 to 170 meters) is used for firing Model 91 grenade.

[Figure 185. Model 89 (1929) 50-mm grenade discharger with various types of ammunition and equipment.]
Figure 185. Model 89 (1929) 50-mm grenade discharger with various types of ammunition and equipment.

(2) Characteristics.

Caliber       50-mm (1.97 inch).
Weight10 1/4 pounds
Range (Model 89 shells)120 meters (131 yards) to 670 meters (737 yards).

(3) Ammunition. The following types of ammunition are known to be provided: Model 89 High explosive shell, model 91 grenade, smoke shell, model 94 practice shell, pyrotechnic signals (described in chapter 10), and incendiary (fig. 186). The incendiary shell has a light metal body and weighs approximately 1.25 pounds. It contains about 0.7 pound of incendiary mixture. The smoke shell weighs approximately 2 pounds, contains about 4 ounces of HC type smoke mixture. The body has the same shape as the high explosive shell, but may be distinguished by Inning two white bands on the body.

[Figure 186. 50-mm grenade discharger shell, incendiary.]
Figure 186. 50-mm grenade discharger shell, incendiary.

d. Model 98 (1938) 50-mm mortar. (1) General description. This is a smooth-bore muzzle loaded weapon with fixed elevation of approximately 40° and limited traverse (fig. 187). It is fired by a lanyard attached to a friction primer affixed to the base of the tube. A special feature is a range slide which may be clamped to the muzzle. This regulates the length of the stick (spigot) extending into the barrel. The greater the distance the stick extends into the barrel, the greater the range.

[Figure 187. Model 98 (1938) 50-mm mortar with projectile.]
Figure 187. Model 98 (1938) 50-mm mortar with projectile.

(2) Characteristics.

Length of barrel       25 inches.
Total weight (complete with base)48 pounds.
Weight of ammunition10 pounds.
FuseTime (activated by friction igniter).

(3) Ammunition. The weapon fires a stick bomb weighing approximately 10 pounds and containing 7 pounds of picric acid in blocks. A smaller bomb containing 5 pounds of picric is also used. A finned bangalore torpedo may also be fired. No other ammunition has been recovered to date.

e. Model 11 (1922) 70-mm mortar. (1) General description. This is an obsolescent muzzle-loaded, rifle-bore weapon (fig. 188). The barrel is supported by a single elevating screw. The markings on the breech end of the barrel [11th year model high angle infantry gun] read "11th year model high angle infantry gun." The latch pin on the breech end of the barrel must be set in to release the safety device. The weapon is fired by means of a lanyard attached to the striker arm.

[Figure 188. Model 11 (1922) 70-mm mortar.]
Figure 188. Model 11 (1922) 70-mm mortar.

(2) Characteristics.

Caliber       70-mm (2.76 inch).
Total weight (including base-plate)133.75 pounds.
Elevation37° to 77°.

(3) Ammunition. The high explosive shell has the propellant powder in its base and operates in the same manner as the model 89 grenade discharger shell previously described.

f. 70-mm barrage mortar. This is a smooth-bore, muzzle-loaded weapon of very simple construction (fig. 189). It fires a shell probably designed for use against low flying aircraft (fig. 189), or firing over the heads of ground troops. When fired, the projectile reaches a range of 3000 to 4000 feet when it expels parachute-supported high explosive charges 11/16 inch in diameter and 3 inches long which in turn explode in the air. If an unexploded shell be found on the ground, it should be marked "Dangerous" and left for disposal by trained personnel.

[Figure 189. 70-mm barrage mortar showing spike and block used as base.]
Figure 189. 70-mm barrage mortar showing spike and block used as base.

[Figure 190. Shell used in 70-mm barrage mortar and its method of functioning.]
Figure 190. Shell used in 70-mm barrage mortar and its method of functioning.

g. Model 97 (1937) 81-mm mortar. (1) General description. This weapon is very similar to United States 81-mm mortar M1. It is a smooth-bore, muzzle-loading, high-angle fire weapon, (fig. 191) which breaks down into 3 sections for transport. The markings [97 model small trench mortar] which appear on the base of the barrel read "97 model small trench mortar." The mortar is provided with a collimator sight which is heavier and more complex than the U.S. M1 sight.

[Figure 191. Model 97 (1937) 81-mm mortar.]
Figure 191. Model 97 (1937) 81-mm mortar.

(2) Characteristics.

Caliber       81-mm (3.19-inch).
Maximum range (light shell)3,100 yards (approximately).
Length of barrel49 1/2 inches.
Total weight145 pounds.
Weight of shell6.93 pounds (1 pound of TNT).

(3) Ammunition. This weapon fires high explosive shells which are interchangeable with the United States M43 81-mm light shell. Heavier shells have been reported but no specimens have been recovered. The fuzes can be adjusted to give instantaneous or delay action detonations.

h. Model 99 (1939) 81-mm mortar. (1) General description. Model 99 is similar to model 97 except that it has a much shorter barrel and is equipped for trigger firing with a mechanism at base of the barrel (fig. 192).

[Figure 192. Model 99 (1939) 81-mm mortar and standard projectile.]
Figure 192. Model 99 (1939) 81-mm mortar and standard projectile.

The weapon is fired by hitting the protruding end of the firing pin cam shaft with a wooden mallet.

For transport, this mortar breaks down into three sections, each weighing approximately 17 pounds. It may be fired with United States M43 81-mm mortar shells, in which case a maximum range of 2,500 yards may be obtained.

(2) Characteristics.

Caliber       81-mm (3.19-inch).
Maximum range2,200 yards.
Length of barrel25 1/4 inches.
Total weight52 pounds.

(3) Ammunition. HE and smoke or chemical shells have been recovered. The fuse may be adjusted for instantaneous or delay detonation.

i. Model 94 (1934) 90-mm mortar. (1) General description. This is a smooth-bore, muzzle-loading weapon with a fixed firing pin (fig. 193). A special feature is the recoil system, consisting of two recoil cylinders on a one piece U-shaped frame with cylinders located on each side of the barrel. The Japanese markings on the base of the barrel [94 model light trench mortar] read "94 model light trench mortar."

[Figure 193. Model 94 (1934) 90-mm mortar.]
Figure 193. Model 94 (1934) 90-mm mortar.

(2) Characteristics.

Caliber       90-mm (3.54-inch).
Maximum range4,150 yards.
Length of barrel52 inches (approximately).
Total weight340 pounds.
SightPanoramic telescope sight.

(3) Ammunition. Model 94 mortar fires HE and incendiary ammunition. The incendiary shell is 16 inches long, weighs 11.5 pounds. The mixture is white phosphorus, carbon disulphide and 40 impregnated rubber pellets. This shell can be identified by a red band below the fuse, a blue band between the fuze and bourrelet, a yellow band between the bourrelet and fin, and a white band at the junction of the shell body and the fin. The fuze may be adjusted to give either instantaneous or delayed detonation.

j. Model 93 (1933) 150-mm mortar. (1) The photograph (fig. 194) shown is believed to be that of the model 93 (1933) 150-mm mortar, a smooth-bore, muzzle-loaded, lanyard fired weapon.

[Figure 194. A probable Model 93 (1933) 150-mm in action.]
Figure 194. A probable Model 93 (1933) 150-mm in action.

(2) Characteristics reported.

Caliber       150-mm (5.9 inch).
Maximum range2,100 meters (2,300 yards).
Length of tube59 inches (approximately).
Weight of tube220 pounds (approximately).
Elevation43° to 80°.

(3) Ammunition. Projectile reported as weighing (total) 56 pounds and containing approximately 14 pounds of explosive.

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