 A new pressurised water reactor, the Rolls-Royce PWR 2, was designed for the "Vanguard" class.The PWR 2 has double the service life of previous models, and it is estimated that a "Vanguard"-class submarine could circumnavigate the world 40 times without refuelling.Furthermore, during their long-overhaul refit periods, a 'Core H' reactor is fitted to each of the boats, ensuring that none of the submarines will require further re-fuelling for the rest of their service lives.