 The anti-torpedo bulges of the G3 battlecruisers were intended to withstand the explosion of a 750-pound (340 kg) torpedo warhead. They consisted of an outer air space, an inner buoyancy space and the torpedo bulkhead that consisted of two layers of .875-inch (22 mm) high-tensile steel. The bulkhead was situated some 13.5 feet (4.1 m) inboard from the side of the ship. Postwar tests done on a replica of this system showed that filling the buoyancy space with water rather than the sealed steel crushing tubes as used in Hood was just as effective and weighed less. A compressed air system was fitted to blow the water out of the buoyancy spaces and bring the ship upright in 15 minutes after two torpedo hits. The ship's double bottom ranged from 5 – 7 feet (1.5 – 2.1 m) in depth.
