The Tauchpanzer was produced by sealing all openings on the Panzer III using a waterproof compound. The gap between the turret and the hull was closed with an inflatable rubber ring, while rubber sheeting covered the commander’s cupola, the mantlet and the hull machine gun. The engine intakes were blocked with rubber seals, while the exhaust stacks were given non-return valves to prevent water reaching the engine that way. The rubber seals were fitted with explosive charges to allow them to be removed from inside the tank. In case the waterproofing failed the tanks were equipped with pumps. Air was supplied by an 18m long flexible hose, attacked to a buoy floating on the surface, with a 1.50m air intake stack above the buoy. Maximum operating depth was 15m, and the tank was designed to stay underwater for no more than twenty minutes (WIKI)