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.
|Caliber (measured)|| ||3.213 in|
|Length of bore||21.5 in|
|Overall length of barrel||25.25 in|
|Dimensions of base plate||14.25 in|
|Total weight||52 lbs|
|Weight of barrel||17.5 lbs |
|Weight of bipod||16.5 lbs|
|Weight of baseplate||18 lbs|
|Weight of shells||7.2 and 14.3 pounds|
| 7.2-pound shell||545 to 3,280 yards.|
| 14.3-pound shell||207 to 1,312 yards.|
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
(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.