A submarine is a specialized watercraft that can operate underwater. Submarines, first widely used in World War I, are used by all major navies today, especially the American, British, French and Russian navies. Civilian submarines and submersibles are used for marine and freshwater science and for work at depths too great for human divers.
Nuclear powered submarines and other large submarines are classed as ships, but are customarily referred to by their crews as "boats". The term U-Boat is sometimes used for German submarines in English. This comes from the German word for submarine, 'U-Boot', itself an abbreviation for Unterseeboot ('undersea boat').
Submarines encompass one of the largest ranges in capabilities of any vessel. They range from small two-man vessels that can examine the sea floor for a few hours to the Russian Typhoon class, which can remain submerged for half a year and carry enough nuclear missiles to destroy hundreds of cities. There are also specialized submarines such as rescue submarines (like the DSRV or Priz) and tiny one-person human powered subs intended for competitions between universities. An older device for use in underwater exploration, salvage, construction and rescue is the diving bell.
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Underwater Vehicles :: Scuba Diving

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