 The anti @-@ torpedo bulges of the Admiral @-@ class battlecruisers were the first fitted on a British capital ship to fully incorporate the lessons learned from a series of experiments begun before World War I. They consisted of an outer air space , an inner buoyancy space and the 1 @.@ 5 @-@ inch protective bulkhead . The buoyancy space was filled with sealed steel crushing tubes intended to distribute the force of an explosion over as wide an area as possible as well as absorb as much of its force as possible . However , tests conducted after Hood was completed showed that filling the buoyancy space with water was equally as effective and considerably cheaper . 
