Submarines

Submarine, naval vessel designed principally for underwater operations and equipped with guided missiles and torpedoes as its basic weapons.
The modern submarine is a watertight craft with a welded, cigar-shaped hull. Most of it is occupied by the pressure hull, an inner chamber designed to withstand the tremendous pressures experienced at great ocean depths; the remainder consists of an outer chamber that houses ballast tanks. Rising from the hull is a structure called the sail. Known as the conning tower on older submarines, the sail of a modern nuclear submarine houses periscopes, radar and radio masts, snorkel, and diving planes. During surface operation the sail serves as the vessel's bridge. When submerged, the functions of the bridge are transferred to the control room, which is located in the pressure hull directly below the sail.

To submerge the submarine, water is admitted to the ballast tanks in sufficient quantities to sink it to the desired depth. Resurfacing is accomplished by the use of compressed air to force the water out of the tanks. At the bow or sail, and at the stern, are horizontal rudders, known as diving planes, which give the vessel longitudinal stability when diving or rising.