The hull was built in three sections composed of 3 millimetres (0.12 in) thick steel with an aluminium alloy conning tower bolted to the top.[3] The conning tower contained armoured glass windows to allow the pilot to see out.[3] 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.[3] Adding to the pilot’s difficulties, the craft lacked compensating and trimming tanks, making staying at periscope depth a near impossibility.[3] The Biber had two diving tanks, one in the bow section and one in the stern.[2]