The hull was built in three sections composed of thick steel with an aluminium alloy conning tower bolted to the top. The conning tower contained armoured glass windows to allow the pilot to see out. The hydroplanes and rudder were made of wood and trying to control them while tracking the depth gauge, compass and periscope made the craft hard to handle. Adding to the pilot’s difficulties, the craft lacked compensating and trimming tanks, making staying at periscope depth a near impossibility. The Biber had two diving tanks, one in the bow section and one in the stern.