The US Navy built the first aircraft carrier to be powered by nuclear reactors. was powered by eight nuclear reactors and was the second surface warship (after ) to be powered in this way. The post-war years also saw the development of the helicopter, with a variety of useful roles and mission capability aboard aircraft carriers and other naval ships. In the late 1950s and early 1960s, the United Kingdom and the United States converted some older carriers into Commando Carriers or Landing Platform Helicopters (LPH); seagoing helicopter airfields like . To mitigate the expensive connotations of the term "aircraft carrier", the carriers were originally designated as "through deck cruisers" and were initially to operate as helicopter-only craft escort carriers.