Experience with the turbocharged versions of the company’s earlier Whirlwind helicopter during the 1950s gave Westland a good appreciation of the capability of a helicopter with such a powerplant. This ultimately led to Westland commencing negotiations with the American Sikorsky company to manufacture the Sikorsky S-58 helicopter under license for employment by the Royal Navy in the Anti-Submarine (ASW) role. It was rather hoped that this new machine would be able to combine both the Hunter and Killer activities formerly performed by two-aircraft Whirlwind teams but operational trials soon revealed that this would not be entirely practicable.
Development of the British machine would commence with the modifying of the single S-58 received from Sikorsky with the replacement of the American Wright R-1820 piston engine with a Napier Gazelle NGa.11 turboshaft, and it was with this powerplant that the first machine (Later to become the company’s demonstrator) which first took to the air on the 17th May 1957.
Satisfactory testing of the prototype and two pre-production examples (Gazelle Mk161 engines) led to acceptance of the type for the Royal Navy (FAA) as the, now named. Wessex HAS. Mk.1 (of which some 130 would be built), and the Royal Air Force as the HAS. Mk.2. The main difference between the two types (other than in specialist service equipment) was that the Mk.2 was powered by twin coupled Bristol Siddeley Gnome turboshafts which allowed the rotors to remain powered even in the eventuality of engine failure by one engine. The Royal Navy’s Wessex helicopters would be employed mainly as Hunter-Killer pairs in the ASW role and by the Royal Marines as transports carrying up to 16 fully armed Commandos. The RAF’s HAS Mk.2 were deployed in ambulance and general Utility roles.
Later versions were the Mk3 powered by a more powerful Gazelle NGa 22 powerplant which allowed for the entire ASW mission to be carried out automatically; The Mk 4 (a pair of VIP transports for the Queens Flight); The Mk 5 ( a specialist troop transport for the Royal Marines, and the Wessex Mk 60 for the civilian market. Export models were the Wessex HAS Mk 31 and 31b for the Australian Navy and the Wessex Mk 52, Mk 53 and Mk 54 for Iran, Ghana and Brunei respectively.
Whilst replaced in the front line ASW duties during the 1960s by the Sea King Mk 6 many Wessex helicopters have continued to provide useful service for many years in Search and Rescue duties and occasionally (as in Northern Ireland1) as supplementary troop transports to the Army’s Lynx helicopters.