Shinyo boats and the defence of Japan's home islands

The Shinyo programme produced one- and two-man explosive boats, while the Army separately developed the Maru-Ni, competing for resources through a parallel programme. Some arrangements allowed the crew to leave before detonation despite the boats' inclusion in the special-attack system. Navy boats could carry 300 kilograms of explosives in the bow, while the Army design dropped two depth charges and attempted to turn away before they exploded. Production reached at least 6,197 Shinyo and more than 3,000 Maru-Ni, leaving thousands available for the defence of the home islands. Allied forces preferred to destroy concentrations in harbours or caves before the boats could launch. At sea, layered screens of small craft and supporting warships continued methods already used around Sicily and Normandy. Royal Navy study of Okinawa and the deployment of Battle-class destroyers supported preparations for a possible invasion of Japan. A coordinated attack with conventional motorboats and aircraft could have divided the screen's attention and made the explosive boats harder to stop.