Torpedo bulkhead

It is designed to keep the ship afloat even if the hull is struck underneath the belt armor by a shell or by a torpedo.

A significant problem with these early arrangements was that once the coal was depleted, the empty compartments offered little to no resistance; worse still, coal dust could explode, and given that the bunkers needed to be accessed by boiler room crews, they could not easily be made watertight.

[1] In the 1910s, naval designers began to transition from coal to fuel oil to power their ships; bunkers filled with liquid fuel proved to be much more effective at absorbing the blast effects of an underwater explosion, and unlike coal bunkers, they could be filled with water once emptied.

During this period, many designers also began to adopt multi-layered protection schemes, some of which were also coupled with anti-torpedo bulges, to improve the survivability of their ships.

The historian Roger Branfill-Cook characterizes the American Tennessee-class battleships, designed in 1915, as having the best layout of the period, which featured three armored bulkheads layered between three liquid-filled compartments, and placed between an empty void and unarmored bulkhead on either side.