The Westland WS-61 Sea King is a British license-built version of the American Sikorsky S-61 helicopter of the same name, built by Westland Helicopters. The aircraft differs considerably from the American version, with Rolls-Royce Gnome engines (licence-built General Electric T58s), British made anti-submarine warfare systems and a fully computerised control system. The Westland Sea King was also produced as the Commando troop transport version for export.
Westland Helicopters, which had a long standing licence agreement with Sikorsky to allow it to build Sikorsky's helicopters, extended the agreement to cover Sikorsky Sea King soon after the Sea King's first flight in 1959. In 1966 the British Royal Navy selected the Sea King to meet a requirement for an anti-submarine warfare helicopter to replace the Westland Wessex, placing an order with Westland for 60 Sea Kings on 27 June 1966. The prototype and pre-production aircraft were constructed with Sikorsky-built components. The first Westland-built aircraft, the first production aircraft for the Royal Navy designated the Sea King HAS1, first flew on the 7 May 1969 and was delivered to the navy in the same year.