Towards the end of 1943, in response to unfavorable progress in the war, the Japanese command heard suggestions for various suicide craft. These suggestions were initially rejected but later deemed necessary. For the naval department this meant kamikaze planes, kaiten submarines, fukuryu suicide divers or human mines and shinyo suicide boats.
These fast motorboats were driven by one man, to speeds of around 30 knots. They were typically equipped with a bow-mounted charge of up to 700 pounds of explosives that could be detonated by either impact or from a manual switch in the driver's area. These attack boats also carried two anti-ship rockets mounted on launchers located on either side of the boat behind the driver.
The similar Maru-ni, which were used by the Imperial Japanese Army, were equipped with two depth charges, and were not actually suicide boats, as the idea was to drop the depth charges and then turn around before the explosion took place. Although the chances of boat and crew surviving the wave from the explosion might seem slim, a small number of crewmen successfully escaped. The depth charges used were known as the Experimental Manufacture Use 120 kg Depth Charge, and were armed by a delayed-action pull igniter.