Submarine


A submarine is a expert watercraft that can work underwater at very high pressures beyond the range of unaided human survivability. Submarines, first commonly used in World War I, are used by all major navies today, especially the American, Russian and British navies. Civilian submarines and submersibles are used for marine and freshwater science and for work at depths too large for human divers.
Submarines are always referred to as "boats" excluding in some formal documents. The term U-Boat is occasionally used for German submarines in English. This comes from the German word for submarine, 'U-Boot', itself an short form for Unterseeboot ('undersea boat').
Submarines encompass one of the biggest ranges in capabilities of any vessel. They range from small one- or two-man vessels that can check the sea floor for a few hours to the Russian Typhoon class, which can remain submerged for half a year and carry nuclear missiles capable of destroying several cities. There are also specialized submarines such as rescue submarines (like the DSRV or Priz) and tiny one-person human power-driven subs intended for competitions between universities. An older device for use in underwater exploration, salvage, building and rescue is the diving bell.
The word submarine was an adjective meaning "under the sea". Some firms who make diving gear but not parts for submarines, called their work "submarine engineering". "Submarine" as a meaning of submersible craft originated as short for "submarine boat" and older books such as Twenty Thousand Leagues Under the Sea always use this term. Also, some people simply say 'sub' as a substitute of saying the entire word 'submarine'.