Submarine
A submarine is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. They were first widely used during World War I (1914–1918), and are now used in many navies, large and small. Military uses include attacking enemy surface ships or other submarines, and for aircraft carrier protection, blockade running, nuclear deterrence, reconnaissance, conventional land attack, and covert insertion of special forces.
