The Westland Wessex is a British-built turbine-powered development of the Sikorsky S-58 "Choctaw", it was developed and produced under license by Westland Aircraft (later Westland Helicopters). One of the main changes from Sikorsky's S-58 was the replacement of the piston-engine powerplant with a turboshaft engine; the Wessex was the first helicopter in the world produced in large numbers that used gas turbine propulsion system. Early models were powered by a single Napier Gazelle engine, later builds used a pair of Rolls-Royce Gnome engines.

The Wessex was initially produced for the Royal Navy (RN) and later for the Royal Air Force (RAF); a limited number of civilian aircraft were also produced, as well as some export sales. The Wessex operated as an anti-submarine warfare and utility helicopter; it is perhaps best recognised for its use as a search and rescue (SAR) helicopter. The type entered operational service in 1961, and had a service life in excess of 40 years before being retired in Britain.

RN anti-submarine version with improved avionics with a radome on the rear fuselage, 3 new-build development aircraft and 43 converted from HAS.1

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