Submarines: How They Work - Archimedes' Principle

In 1954, the U.S. commissioned the first nuclear-powered submarine, the USS Nautilus. Because nuclear-powered engines required no air, the submarine could stay submerged indefinitely, surfacing only when in need of supplies. The Nautilus could travel at speeds of 23 knots surfaced and submerged.

A nuclear-powered engine works because heat is generated by the fissioning of the nuclear fuel. Two systems of pressurized water are sent through the nuclear engine. The first, or primary, system circulates water through the reactor, piping loops, pumps and finally to the steam generators, where the heat from the reactor is transferred to the secondary water system. The water from the primary system is then directed back to the reactor to be heated again. The heat transferred to the secondary system creates steam. This steam supplies the ship with electricity and propulsion when it moves through the turbine generators and propulsion turbines, respectively. The steam, condensed back to water, returns to the steam generators to be reheated.