A nuclear submarine is a submarine powered by a nuclear reactor. The performance advantages of nuclear submarines over "conventional" (typically diesel-electric) submarines are considerable:nuclear propulsion, being completely independent of air, frees the submarine from the need to surface frequently, as is necessary for conventional submarines; the large amount of power generated by a nuclear reactor allows nuclear submarines to operate at high speed for long durations; and the long interval between refuellings grants a range limited only by consumables such as food. The United States launched the USS Nautilus, the first nuclear submarine, in 1954. The Soviet Union soon followed the United States in developing nuclear-powered submarines in the 1950s. Stimulated by the U.S. development of the Nautilus, Soviet work on nuclear propulsion reactors began in the early 1950s at the Institute of Physics and Power Engineering, in Obninsk, under Anatoliy P. Alexandrov, later to become head of the Kurchatov Institute. In 1956, the first Soviet propulsion reactor designed by his team began operational testing. Meanwhile, a design team under Vladimir N. Peregudov worked on the vessel that would house the reactor.