Kingston valve

[2] When opened from the ship's interior,[3] the Kingston valve allows sea water to enter the tank.

[3] Water, controlled by a Kingston valve, could be deliberately taken on board to act as ballast below the waterline.

This Kingston valve, controllable both manually and hydraulically, is known by some as main vent operating gear.

The trapped air in the tank provides positive buoyancy while on the surface, although sea water sloshing in through the flood ports must be removed occasionally from the ballast tank(s) when cruising on the surface by means of low pressure air.

In the vent riser is a valve that when shut, prevents flooding the tank when the submarine is rigged for surface.

Famous examples include the Russian battleships Sevastopol and Potemkin in 1905, the interned Imperial German High Seas Fleet at Scapa Flow in 1919, the Japanese battleship Tosa in 1925, or the German aircraft carrier Graf Zeppelin in 1945.

The Imperial Japanese Navy battleship Kirishima was scuttled by the opening of her Kingston valves, after she had received extensive damage during the Second Naval Battle of Guadalcanal.