Underwater protection and subdivision

The final element of the protection scheme of the first dreadnoughts was the subdivision of the ship below the waterline into several watertight compartments. If the hull was holed—by shellfire, mine, torpedo, or collision—then, in theory, only one area would flood and the ship could survive. To make this precaution even more effective, many dreadnoughts had no hatches between different underwater sections, so that even a surprise hole below the waterline need not sink the ship. However, there were still a number of instances where flooding spread between underwater compartments.[71] The greatest evolution in dreadnought protection came with the development of the Anti-torpedo bulge and torpedo belt, both attempts to protect against underwater damage by mines and torpedoes. The purpose of underwater protection was to absorb the force of a detonating mine or torpedo well away from the final watertight hull. This meant an inner bulkhead along the side of the hull, which was generally lightly armored to capture splinters, separated from the outer hull by one or more compartments. The compartments in between were either left empty, or filled with coal, water or fuel oil.[72]