The Westland Wessex is an early turbine-powered helicopter produced by the British rotorcraft specialist Westland Aircraft (later Westland Helicopters). It was an under licence development of the piston-engined Sikorsky S-58. During the mid-1950s, Westland arranged with the American helicopter manufacturer Sikorsky Aircraft to demonstrate one of its S-58s in Britain to garner sales.
Having secured an order from the Royal Navy (RN), Westland implemented several modifications to the S-58 design ahead of quantity production in the UK. One major change from Sikorsky's S-58 was the replacement of the piston-engine powerplant with a turboshaft engine; while early models were powered by a single Napier Gazelle engine, later builds used a pair of de Havilland Gnome engines.
The use of a turboshaft engine was credited with increasing payload capacity while reducing both vibration and noise levels. The Wessex was first introduced by the RN in 1961; it was the service's first purpose-build anti-submarine helicopter. Multiple variants of the type were introduced, including more capable anti-submarine models (enabling early Wessex HAS.1s to be reassigned to search and rescue (SAR) duties) and a dedicated battlefield transportation variant, the Wessex HU.5; the latter was equipped with two Gnome engines that provided double the power of the HAS.1's single powerplant.
