Steam turbine
Current usage

Since the 1980s, steam turbines have been replaced by gas turbines on fast ships and by diesel engines on other ships; exceptions are nuclear-powered ships and submarines and LNG carriers. Some auxiliary ships continue to use steam propulsion.

In the U.S. Navy, the conventionally powered steam turbine is still in use on all but one of the Wasp-class amphibious assault ships. The Royal Navy decommissioned its last conventional steam-powered surface warship class, the Fearless -class landing platform dock, in 2002, with the Italian Navy following in 2006 by decommissioning its last conventional steam-powered surface warships, the Audace -class destroyers. In 2013, the French Navy ended its steam era with the decommissioning of its last Tourville -class frigate. Amongst the other blue-water navies, the Russian Navy currently operates steam-powered Kuznetsov -class aircraft carriers and Sovremenny -class destroyers. The Indian Navy currently operates INS Vikramaditya, a modified Kiev -class aircraft carrier; it also operates three Brahmaputra -class frigates commissioned in the early 2000s. The Chinese Navy currently operates steam-powered Kuznetsov -class aircraft carriers, Sovremenny -class destroyers along with Luda -class destroyers and the lone Type 051B destroyer. Most other naval forces have either retired or re-engined their steam-powered warships. As of 2020, the Mexican Navy operates four steam-powered former U.S. Knox -class frigates. The Egyptian Navy and the Republic of China Navy respectively operate two and six former U.S. Knox -class frigates. The Ecuadorian Navy currently operates two steam-powered Condell -class frigates (modified Leander -class frigates).

Today, propulsion steam turbine cycle efficiencies have yet to break 50%, yet diesel engines routinely exceed 50%, especially in marine applications. Diesel power plants also have lower operating costs since fewer operators are required. Thus, conventional steam power is used in very few new ships. An exception is LNG carriers which often find it more economical to use boil-off gas with a steam turbine than to re-liquify it.

Nuclear-powered ships and submarines use a nuclear reactor to create steam for turbines. As of 2024, the main propulsion steam turbines (HP & LP) for United States Navy nuclear-powered Nimitz and Ford class aircraft carriers are manufactured by the Curtiss-Wright Corporation in Summerville, SC.

Nuclear power is often chosen where diesel power would be impractical (as in submarine applications) or the logistics of refuelling pose significant problems (for example, icebreakers). It has been estimated that the reactor fuel for the Royal Navy 's Vanguard -class submarines is sufficient to last 40 circumnavigations of the globe – potentially sufficient for the vessel's entire service life. Nuclear propulsion has only been applied to a very few commercial vessels due to the expense of maintenance and the regulatory controls required on nuclear systems and fuel cycles.
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