The Type 4 20cm Roketto: Japan's Rocket Mainstay

(U.S. Army Signal Corps)

     The Germans, U.S., British, and especially the Russians made use of unguided rockets to augment standard artillery and provide for rapidly delivered, devastating bombardments against opposing forces. The Japanese, on the other hand, did not and by the time they realized the value of rockets, the effort put forward to deploy rocket systems was too little, too late. One such rocket system which did make it into service was the Type 4 20cm rocket launcher. 

     First issued in 1943, the Type 4 was actually a 203mm rocket, weighed just over 185lbs. and had a maximum range of 1.4 miles. The Japanese elected to not use fins as a means to stabilize the rocket and instead, it achieved accuracy by means of spin-stabilization. The Type 4 was fired from a standardized launcher which resembled that of a mortar (hence, the Type 4 weapon system often being referred to as a rocket mortar) but it had the advantage of being able to launch from something as simple as a dirt mound. Thus, it was not uncommon for Japanese troops to fabricate launchers in the field. This particular Type 4 was captured by the 4th. U.S. Marine Division during the Battle of Iwo Jima. Unlike the more usual wooden launch rails (which were easier to construct), this Type 4 launcher was far more elaborate. The wheeled carriage made transportation easier as well as allowed for more rapid deployment and had a locking lever to adjust the elevation of the launch tube. The rocket would be loaded into the tube and launched by pulling the long lanyard. The length of the lanyard allowed the firer to be far enough away from the rocket to avoid being struck by debris kicked up by the rocket exhaust. 

     Of all the rocket systems developed, the Type 4 was produced in significant numbers though most of them were kept within Japan to be used to repel the expected Allied invasion of the Japanese home islands…something which never happened.