submarine

A submarine is a watercraft capable of operating underwater independently of surface ships. Submarines can dive and remain submerged for extended periods, although some systems allow partial submersion. They range from small recreational subs to large military boats.

The concept goes back to early experiments such as Cornelius Drebbel's wooden boat in the 1620s, but practical submarines emerged in the 19th and 20th centuries. The Confederate submarine Hunley operated briefly in the American Civil War, and later designs led to modern diesel-electric and nuclear-powered classes.

Most submarines have a pressure hull to withstand deep-water pressure, surrounded by a lighter outer hull or casing. They use ballast tanks to dive and surface. Propulsion has evolved from manpower and battery-powered electric motors to diesel engines for surface running and battery charging, and in the case of many strategic vessels, to nuclear reactors that provide long endurance without refuelling. Some modern subs use air-independent propulsion.

Military submarines perform roles such as sea denial, surveillance, and special operations support. Ballistic missile submarines carry strategic missiles; attack submarines hunt surface ships and submarines and support land forces. Civilian and research submarines explore the deep sea, conduct oceanographic measurements, and assist offshore industries. Submarines rely on sonar and other sensors, periscopes for limited observation, and sophisticated life-support systems for crew.

Submarines continue to shape naval doctrine and ocean science. Ongoing developments include quieter propulsion, improved hull materials, deeper-diving capability, and unmanned underwater vehicles that extend underwater reach beyond manned submarines.