The Nimitz-class supercarriers are a class of ten nuclear-powered aircraft carriers in service with the United States Navy. The lead ship of the class is named for World War II United States Pacific Fleet commander Fleet Admiral Chester W. Nimitz, the U.S. Navy's last fleet admiral. With an overall length of 1,092 ft (333 m) and full-load displacements of over 100,000 long tons,[1] they have been the largest warships built and in service,[4] although they are being eclipsed by the upcoming Gerald R. Ford-class aircraft carriers. Instead of the gas turbines or diesel-electric systems used for propulsion on many modern warships, the carriers use two A4W pressurized water reactors which drive four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h) and maximum power of around 260,000 shp (190 MW). As a result of the use of nuclear power, the ships are capable of operating for over 20 years without refueling and are predicted to have a service life of over 50 years. They are categorized as nuclear-powered aircraft carriers and are numbered with consecutive hull numbers between CVN-68 and CVN-77.