The Kirov class, Soviet designation Project 1144 Orlan, is a class of nuclear-powered guided-missile battlecruisers of the Soviet Navy and Russian Navy, the largest and heaviest surface combatant warships in operation in the world. Among modern warships, they are second in size only to large aircraft carriers; they are similar in size to a World War I-era battleship. Defence commentators in the West often refer to these ships as battlecruisers - due to their size and general appearance. The Soviet classification of the ship-type is "heavy nuclear-powered guided-missile cruiser".

Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Nuclear propulsion is used primarily within naval warships such as nuclear submarines and supercarriers. A small number of experimental civil nuclear ships have been built.