A submarine is a watercraft capable of independent operation underwater. The term most commonly refers to a large, crewed, autonomous vessel. It mainly indicates a warship with a streamlined hull designed to operate completely submerged in the sea for long periods.
The first submersible of whose construction we have reliable information was built in 1620 by Cornelius Drebbel, a Dutchman in the service of James I of England. Although experimental submarines had been built before, submarine design took off during the 19th century, and they were adopted by several navies. Submarines were first widely used during World War I (1914–1918), and now figure in many large navies.
Military usage includes attacking enemy surface ships or submarines, aircraft carrier protection, blockade running, ballistic missile submarines as part of a nuclear strike force, reconnaissance, conventional land attack (for example using a cruise missile), and covert insertion of special forces. Civilian uses for submarines include marine science, salvage, exploration and facility inspection/maintenance. Submarines can also be modified to perform more specialized functions such as search-and-rescue missions or undersea cable repair. Submarines are also used in tourism, and for undersea archaeology.