A new design was needed due to the problems the Japanese Navy had in resupplying troops in the Solomons.
Work on the Ka-Tsu started in 1943. Its primary job was to carry cargo from ship to shore.
There were some shields for the crew but the rest of the Ka-Tsu was unarmored.
The engine compartment was hermetically sealed along with the electric final drives. It was intended for the Ka-Tsu to be delivered by submarine.
Once development was completed there were some in the Japanese Navy who wanted to turn the Ka-Tsus into suicide weapons. The Ka-Tsu was to be armed with two torpedoes. The war ended before they could be deployed.