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.
The last Sea Kings to be built at Westland were tailnumbers 329 and 330. They were Mk 43B SAR Versions for the RNoAF Royal Norwegian Air Force. The last of the Royal Navy's Sea King ASW helicopters was retired in 2003, being replaced by the AgustaWestland Merlin HM1. The Airborne Surveillance and Area Control (ASaC) or Airborne Early Warning (AEW) variant is expected to be replaced in time for the two Queen Elizabeth-class aircraft carriers, some time in the next decade. The types in contention are a Merlin derivative, a V-22 Osprey variant or a derivative of the E-2C Hawkeye. The HC4 commando variant is also expected to be replaced within the next decade along with Search and Rescue variants. In total, 330 Sea Kings were produced.