a direct hit from a explosive warhead; British aerial torpedoes had smaller warheads than this, but their ship-launched weapons were more powerful. The navy conducted several full-scale underwater explosion tests with sections of armor cut from the old pre-dreadnought . The tests revealed that welded steel construction better withstood the impact of the 250 kg warhead than did riveted steel plates. The torpedo bulkhead, composed of Wotan Weich (Wotan, soft) steel, placed behind the armored belt was riveted; this was done because plate joints that had been incorrectly welded would not sufficiently withstand explosive shocks. The underwater protection system was constructed out of several layers: the outer layer that was between 12 and 66 mm (.47–2.6 in) thick, directly underneath the main armored belt, was designed to detonate the torpedo warhead. Behind the outer plate was a large void which would allow gases from the explosion to expand and dissipate. Beyond this was a fuel bunker with an thick outer wall; this would absorb any remaining explosive force. The bunker was supported by longitudinal stiffeners and transverse bulkheads. The underwater side protection had numerous faults. It was extremely strong amidships, but weakened on either end of the citadel. The underwater protection could stop only a warhead in these areas. Another significant weakness in the design was the arrangement of the torpedo bulkhead. It was connected to the lower portion of the sloped deck, at an angle of 10°; two riveted angled bars held it in place. The bars were constantly under a great deal of stress, due to normal bending forces in the hull. When combined with the explosive force of a torpedo warhead, the bars could not sustain the increased pressure and could fail. Also, the beam of 30 m meant that the protection system had to be weaker around the main battery turrets, as a significant amount of the hull space was taken up by the magazines and barbettes. Service history Construction and early actions Gneisenau was laid down on 3 May 1935 at the Deutsche Werke in Kiel. She was launched on 8 December 1936, and completed on 21 May 1938. During her launch, the ship sustained minor damage to her stern; the chains slowing her slide down the slipway broke, and the ship drifted too far and became beached on the opposite shore. After her commissioning, Gneisenau spent the first year of her career conducting trials