The underwater protection system was designed to withstand 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 12–66 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.