Submarine

A submarine is a particular watercraft that can operate underwater at very high pressures beyond the range of unaided human survivability. Submarines extensively used in World War I, are used by all major navies today, especially the American, Russian and British navies.

Submarines are formerly referred to as "boats" except in certain conditions. The term U-Boat (an abbreviation for Unterseeboot ('undersea boat')) is referred for German submarines in English. Submarines cover one of the largest ranges in capabilities of any vessel. There are also specialized submarines like rescue submarines (eg; the DSRV or Priz) and tiny one-person human power-driven subs intended for competitions between universities.