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"Japanese 81-mm Mortar, Type 99" from Tactical and Technical Trends

The following U.S. military report on the Japanese Type 99 81-mm mortar was originally published in Tactical and Technical Trends, No. 41, December 30, 1943.

[DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]


Like the Japanese Model 97 (1937) the 81-mm mortar and the U.S. 81-mm mortar, M1, the Japanese Model 99 (1939) 81-mm is patterned after the Stokes-Brandt type of mortar. Unlike them, it has a shorter barrel, is equipped for trigger firing, and has a close fit between the bore and the projectile to compensate for the shorter barrel.

a. Characteristics

Caliber (measured)     3.213 in
Length of bore21.5 in
Overall length of barrel25.25 in
Dimensions of base plate14.25 in
Total weight52 lbs
Weight of barrel17.5 lbs
Weight of bipod16.5 lbs
Weight of baseplate18 lbs
Weight of shells7.2 and 14.3 pounds
   7.2-pound shell545 to 3,280 yards.
   14.3-pound shell207 to 1,312 yards.

[Japanese 81-mm Mortar, Type 99]

b. Interesting Features

(1) The buffer system incorporated in the bipod, giving recuperation of approximately two inches, the cylinder being filled with a light grease or heavy oil.

(2) A safety device, effecting a withdrawal of the striker.

(3) The use of a turnbuckle between the elevating screw tube and the left bipod leg to effect cross-levelling, the elevating screw tube being pivoted in the bipod crosshead.

(4) A very tight fit between the projectile and the tube to give better sealing of the powder gases, thus compensating for the short tube.

(5) A manually-operated firing pin actuated by a blow on a caming lever protruding from the base of the tube. This arrangement is necessary because the tight fit mentioned above will not permit the projectile to slide down the barrel with sufficient speed to be fired by a fixed firing pin.


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