The Type 4 Ka-Tsu was developed in 1943 and trialed in 1944 following the difficulties experienced in the Solomon Islands of resupplying troops.

Its main purpose was to transport troops and supplies ashore and was designed to be launched from submarines. It was fitted with 10mm of armour to protect against small arms, armed with two 13.7mm machine guns and had a crew of 5. Its twin drive propeller shafts would retract when the vehicle was on land.

Following successful trials it was proposed to use the Ka-Tsu to attack US battleships at anchor by arming them with twin torpedos and launching them offshore. The Ka-Tsu would then move to the outer reef and cross the reef to the enter the lagoon where it could launch its attack. Again, trials were successful but the war ended before the Ka-Tsu could be deployed in combat. A total of 49 Ka-Tsu were produced.