Casing (submarine)

The casing of a

submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...

is a light metal structure, usually incorporating a deck, built over the upper surface of the vessel's pressure hull. The pressure hull of a submarine is usually

cylindrical A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...

and possesses a low freeboard when in the water, which makes walking on the hull when on the surface dangerous in high seas or rough weather. The casing provides a flat and therefore safer platform for personnel to walk on. The casing is outside the pressure hull and free-flooding so is usually

perforated A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a ''perforation''. The process of creating perforations is called perfor ...

with numerous holes, allowing water to enter and trapped air to escape easily, eliminating any buoyancy contributed by the casing and allowing the submarine to submerge with as little delay as possible. Casings have been eliminated since the end of World War II as the flow of water through the numerous flood-holes creates noise that may be detected by an enemy using passive sonar, as well as causing hydrodynamic

drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adj ...

. Submarine design {{Submarine-stub