Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear power plant. The power plant heats water, to produce steam and it is this steam that powers the steam turbines and turbo generators. The power is then transferred to a gearbox that reduces the ratio by around 50 to 1 and this powers the propulsor. Naval nuclear propulsion is propulsion that specifically refers to naval warships (see Nuclear navy). Very few experimental civil nuclear ships have been built.