Torpedo bulkhead

Diagram of common elements of warship armor. The belt armor (A) is on the exterior, at the waterline. Also indicated is the main deck (B), the sloping deck armor (C), and the torpedo bulkhead (D).

A torpedo bulkhead is a type of naval armor common on the more heavily armored warships, especially battleships and battlecruisers of the early 20th century. 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.