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"Japanese Sixty-Kilogram High Explosive Bomb (Type 97)" from Tactical and Technical Trends

The following report on the Japanese Type 97 high-explosive bomb was originally printed in Tactical and Technical Trends, No. 6, August 27, 1942.

[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.]


This bomb is reported to have been used extensively by the Japanese in the Malayan campaign (see accompanying diagram).

The Bomb.

The bomb consists of a steel nose secured by twenty 10-mm. (0.4 in.) rivets to a steel body, at the other end of which is attached a tail assembly with four fins. The body and tail assembly are connected by a steel ring riveted to the tail cone by twenty-four 5-mm. (0.2 in.), rivets and screwed to the body by twenty-eight 5-mm. screws. The casing is identical with that of the 50-kg. incendiary bomb. The type-97 fuse is used in the nose.

[Japanese Sixty-Kilogram High Explosive Bomb (Type 97)]
Japanese Sixty-Kilogram High Explosive Bomb (Type 97)

The Fuse.

(a) Description. The body (1) carries the striker spindle (2) which is held in place by a thin shear wire (3) and by a grub screw (4) which engages in a slot (5) in the spindle. The upper portion of the spindle carries a left-hand thread which screws into a pressure block (6). At the top of the striker spindle is a small screw (7) with a right-hand thread and large head; the function of this screw is to prevent the pressure block (6) from unscrewing completely. The pressure block carries a brass cap (8) with four galvanized iron vanes, the cap being attached to the block by four small screws. A small steel striker (9) is screwed into the bottom of the striker spindle.

(b) Method of functioning. Before the bomb is released the cap and pressure block are screwed firmly down on the striker spindle. The screw (7) bears tightly against the inside of the cap (8) and this prevents the threads on the striker spindle (2) and the pressure block (6) from jamming. The pressure block rests on the shoulder of the main body (1). On release of the bomb from the aircraft, the wire is withdrawn from two loops in the center of the vanes and from the safety wire loop (10). The remaining vanes rotate in a clockwise direction, so that the pressure block and cap are raised off the shoulder of the body (1), the striker (2) being still prevented from moving by the shear wire (3). The vanes are prevented from coming off completely by the screw (7) the thread of which is right-hand and cannot be rotated by the pressure block (6). On impact the cap-pressure block-striker system is forced down, breaking the shear wire; and the detonator functions. The maximum number of rotations of the cap-pressure block system is 5 3/4, the pitch being 3 mm. (0.12 in.), and the striker is approximately 4 mm. (0.16 in.) from the cap. Just over one turn is therefore sufficient to fire the fuse. The body (1) has an internal thread at its lower end, into which a brass gaine or magazine can be screwed.


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