The Rolls-Royce pressurised water reactor (PWR) series has powered the Royal Navy's nuclear submarines since the Valiant class, commissioned in 1966.
HMS Valiant, the first British nuclear submarine to be powered by a British built reactor
A nuclear submarine is a submarine powered by a nuclear reactor, but not necessarily nuclear-armed. Nuclear submarines have considerable performance advantages over "conventional" submarines. 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 periods, and the long interval between refuelings grants a range virtually unlimited, making the only limits on voyage times being imposed by such factors as the need to restock food or other consumables.
British Astute-class submarine
USS Nautilus, the first nuclear-powered submarine.
The smallest nuclear-powered submarine, the U.S. Navy's NR-1.
The nuclear-powered VMF Typhoon-class submarines were the world's largest-displacement submarines.