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Model 96 (1936) 150-mm mortar
Model 97 (1937) 150-mm mortar

The Japanese Army, which relied heavily on the trench mortar for fire support, also developed 150-mm mortars. Type 96 was the largest infantry mortar in IJA. It is said that Type 96 was used in China and Iwo Jima, but its details are unkown.

Type 97 is a simplified model of Type 96 by removing the recoil mechanism. There are two sub-models, the short barrelled model and the long barrelled model. Called a "medium" mortar by the Japanese, this Model 97 (1937) 150-mm weapon is a conventional smooth-bore, muzzle-loading, bipod-mounted mortal1 of sturdy construction. This weapon is the largest Japanese mortar. It was emplaced in a concrete pit with the muzzle level with the top of the pit. The 150-mm mortar shell weighs approximately 57 pounds. The bursting radius is reported to be 65 feet.

This 150-mm mortar, which resembles in design the standard US 81-mm mortar, weighs 770 pounds complete with sight, and fires a conventional type of high-explosive shell weighing approximately 57 pounds. The weapon is sighted by means of a 3-power panoramic elbow telescope, and the Japanese claim it will throw a projectile a maximum 2,187 yards. Bursting radius of the shell is reported to be 65 feet, with some fragments thrown 100 feet further.

For transport, the mortar—including the sight—breaks down into these five component parts:

1. Tube 257 pounds
2. Base Plate 337 pounds
3. Bipod and elevating gear 100 pounds
4. Traversing gear, shock-absorbers, and mortar clamps 71.5 pounds
5. Sight 1.5 pounds

The tube is 75.37 inches long and has a reinforcing muzzle band, while the heavy, ribbed-steel base plate measures 17.75 inches by 35.5 inches. The weapon is assembled, adjusted for fire, and operated like the US 81-mm mortar. However, the firing mechanism resembles that of the Japanese Model 99 81-mm mortar, using a firing-pin cam shaft built into the base-cap, rather than a fixed firing pin.

The Japanese had another Model 97 150-mm mortar, which was reported to weigh 1,540 pounds and to have a maximum range of 3,828 yards. There is a possibility that this mortar may be installed on a mobile mount.