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Imperial Japanese Rocket Weapons / FunShin TsuJo Dan

Although the Japanese were unprepared for rocket warfare when it suddenly became an important factor, there is definite evidence that they were experimenting with rocket-propelled projectiles before they plunged into the war in 1941. Since that time, events proved the Japanese ready to use rocket weapons in land warfare, at least on a limited scale, and there were indications that improvements in Japanese rocket weapons, and an increase in their tactical use was expected.

Japanese interest in rocket-propelled projectiles may be attributed to the Japanese "theory of the heavy shell" and to the inability of Japan's industry to produce heavy artillery on a sufficiently large scale. The "theory of the heavy shell", according to the Japanese military writing, is based upon the premise that the weight of the projectile is the only means of measuring the effectiveness of the weapon from which it is delivered. Heavy artillery, which is cumbersome and expensive, throws a shell that is only a fraction of the weight of the gun.

On the other hand, an equally heavy shell can be thrown from a mortar or a rocket gun which, compared to a heavy artillery piece, is much lighter, more mobile, and cheaper and easier to manufacture. Although heavy artillery can greatly outrange the cheaper weapons, this advantage is offset by the fact that mortars and rocket projectors can be brought sufficiently far forward to engage many targets normally covered by artillery.

Late models showed a strong German influence in their design. The early types of launchers for ground-to-ground rockets were crude metal or wood trough-shaped ramps of various lengths supported at the forward end by some simple form of bipod, usually iron pipe. Through German influence, these models were replaced by the tube-type launcher, some of which were supported by a light two-wheeled carriage with fixed metal frame. Rocket-assisted AA and aircraft missiles were still in the experimental stage at the end of the war.

In May 1944 the Japanese chiefs of ordnance admitted that "it is impossible to supply those types of ordnance which are not available, such as cannon above field artillery class". Undoubtedly this, and the added example of successful Allied and German rocket weapons, has added impetus to the development and manufacture of rockets in Japan. Oddly enough, much of the development of rocket weapons was done by the Japanese Navy. From 04 February until 03 March 1945, the US XIV Corps fought a savage house-to-house battle against some 17,000 Japanese troops who had dug themselves into Manila. It was the only battle during the Pacific Campaign that saw large-scale urban fighting. Although the Japanese had few howitzers, their mortars and rockets could and did produce many casualties. Numerous accounts speak of the terrific morale effect of the Japanese rockets, ranging from 200 to 450-mm.

Japanese rockets and rocket launchers were of no great significance in World War II, although their development and production was rapid after they were introduced near the end of the conflict. The Japanese Army neglected to keep pace with other major armies in the de velopment of modern artillery techniques.