Submarine

The military submarine is a warship designed to operate submerged for extended periods, used to attack surface shipping and other submarines, run blockades, gather intelligence and, in the nuclear era, carry ballistic missiles. Submarines existed in limited form earlier, but they first had a major impact in war during the First World War, when German U-boats fought the First Battle of the Atlantic and sank the passenger liner RMS Lusitania in 1915. Submarine warfare became still more consequential in the Second World War, when Germany's U-boat campaign in the Battle of the Atlantic tried to sink Allied merchant shipping faster than Britain could replace it, a struggle whose outcome bore directly on Britain's ability to stay in the war.