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"The 150-mm Mortar" from Intelligence Bulletin, Feb. 1945

[Intelligence Bulletin Cover]   Report on a captured Japanese Model 97 150-mm mortar, from Intelligence Bulletin, February 1945.

[Editor's Note: The following article is wartime information on enemy equipment and tactics published for Allied soldiers. More accurate data on Japanese weapons and equipment is available in postwar publications.]


The Japanese Army, which has relied heavily upon the trench mortar for fire support, has developed a 150-mm mortar.

Called a "medium" mortar by the Japanese, this Model 97 (1937) 150-mm weapon is a conventional smooth-bore, muzzle-loading, bipod-mounted mortar of sturdy construction. Captured on Peleliu Island, this weapon is the largest Japanese mortar yet found. There it was emplaced in a concrete pit with the muzzle level with the top of the pit.

This 150-mm mortar, which resembles in design the standard U.S. 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:
Tube  . . . . .  257 pounds
Base Plate  . . . . .  337 pounds
Bipod and elevating gear  . . . . .  100 pounds
Traversing gear, shock-absorbers, and mortar clamps   . . . . .  74.5 pounds
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 47.75 inches by 35.5 inches.

[Japanese Model 97 150-mm mortar]
The Japanese Model 97 150-mm mortar, largest enemy weapon of this type yet encountered by U.S. troops in the Pacific.

[Japanese Model 97 150-mm mortar shell]
The 150-mm mortar shell weighs approximately 57 pounds. The bursting radius is reported to be 65 feet.

The weapon is assembled, adjusted for fire, and operated like the U.S. 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 are known to have another Model 97 150-mm mortar, which has not yet been encountered. It is 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.

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