Type 4 70 mm AT Rocket Launcher

The Type 4 70 mm AT Rocket Launcher was a Japanese rocket launcher used during the last year of World War II. It was to be used in the Japanese mainland in case of an invasion by the Allies.

It is comparable to the German Panzerschreck and the American Bazooka.

History
By 1944 the Americans were using M1 Bazooka anti tank rocket launchers in the Pacific Theater against the Japanese. Japanese military commanders decided that they needed a similar weapon. In 1944 they adopted the Type 4 70mm rocket launcher. Unlike the US rocket that used fins to stabilize it in flight, the Japanese rocket had angled venturis in the base to spin the rocket for stability. The 20 cm (8”) HE rocket used by the Japanese was also spin-stabilized so they were familiar with the production of this type of rocket.

Development
The launcher was made in two parts that were joined in the middle, similar to the US 3.5” Rocket Launcher. It was designed to be fired by a soldier while prone. The weapon itself had a bipod similar to the one on the Type 99 LMG (Light Machine Gun). The gunner lay with his body at approximately a 45 degree angle to the bore on the left side while the loader was similarly positioned on the other side. The pistol grip and trigger mechanism were attached to the rear half of the launcher. A cable ran from the trigger to the rear of the launcher where the hammer was located. The hammer and firing pin was mounted on an arm that looks like a mouse trap mechanism. The arm was above the bore and out of the way of loading the rocket when it was in the cocked position. Pulling the trigger pulled the pin holding the arm in position and the arm swung around under spring pressure, striking the primer and igniting the rocket.

The 70mm rocket, like the 20 cm model, used a mortar fuze. There would be no set back when the rocket was fired to arm an artillery fuze. The Japanese mortar fuse for the 81mm and 90mm used a simple shear wire to make it bore safe. The wire went through the brass body and aluminum firing pin plunger. Upon impact the plunger was forced back, shearing the wire and freeing the plunger to strike the firing pin and detonate the round. This system would work well with a rocket and was already available in the Japanese supply system.