Submarine hull

A submarine hull has two major components, the superstructure and the pressure hull. The external portion of a submarine’s hull—that part that does not resist sea pressure and is free-flooding—is known as the “superstructure” in American submarine terminology and the “casing” in British submarine terminology. It is sometimes also referred to as the “light hull” or other descriptive terms.

The superstructure (casing in British usage) of a submarine is the outer non-watertight, “free-flooding” hull which provides a hydrodynamically efficient shape. The pressure hull is the inner hull of a submarine that resists sea pressure and maintains the submarine’s structural integrity at (operating) depth.