The Westland Wessex is a British-built turbine-powered development of the Sikorsky H-34, developed and produced under license by Westland Aircraft, later Westland Helicopters, between 1958 and 1970. A total of 382 were produced. One of the main changes from Sikorsky's H-34 was the replacement of the piston-engine power plant with a turboshaft engine; the Wessex was the first helicopter in the world to be produced in large numbers that made use of a gas turbine propulsion system. Early models were powered by a single Napier Gazelle engine, , The Gazelle engine was lighter by 600 lb than its design predecessor, and this required some redistribution of weight. Later builds used a pair of Rolls-Royce Gnome engines.
In service, the Wessex was found to be a major improvement over the older Westland Whirlwind. The revolutionary turbine propulsion, in addition to giving the Wessex a larger load capacity, was quieter and generated less vibration, the latter quality was highly beneficial when treating casualties during flight. The early Gazelle engines allowed for rapid starting and thus faster response times.
The Wessex could also operate in a wide range of weather conditions as well as at night, partly due to its use of an automatic pilot system.
As an anti-submarine helicopter, the Wessex could be alternatively equipped with a dipping sonar array to detect and track underwater targets or armed with either depth charges or torpedoes; a single Wessex could not be equipped to simultaneously detect and attack submarines as this was beyond its carrying capacity. It was this limitation that soon led the Royal Navy to search for a more-capable helicopter that could provide this capability; which would ultimately result in Westland proceeding with the adaptation and production of another Sikorsky-designed helicopter, the Westland Sea King.
An improved variant, the Wessex HAS3, succeeded the HAS1 in the anti-submarine role; it featured more capable radar and better avionics, greater engine power, improved navigational features and a more advanced weapon system; the original HAS1 were hence re-tasked for SAR duties.
Operationally, younger models would be assigned to perform the key anti-submarine warfare and commando transport missions, while older and less capable models would be typically be assigned to land bases for search and rescue (SAR).
The Wessex was also successfully employed as a general-purpose helicopter for the RAF, capable of performing troop-carrying, air ambulance and ground support roles. The Wessex was the first of the RAF's helicopters in which instrument flying, and thus night time operations, were realistically viable.
A 'commando assault' variant, the Wessex HU5, was also developed as a battlefield transportation helicopter; it was typically deployed upon on the navy's amphibious assault ships, such as the commando carrier HMS Albion, and was heavily used to transport the Royal Marines.
The Wessex's service career featured long-term deployments to both Hong Kong and Northern Ireland to support internal security operations, performing transport and surveillance missions.
In 1962, an international crisis arose as Indonesia threatened confrontation over the issue of Brunei, which was not in the newly formed Federation of Malaya. By February 1964, a large number of RAF and RN helicopters, including Westland Wessex, were operating from bases in Sarawak and Sabah to assist Army and Marine detachments fighting guerrilla forces infiltrated by Indonesia over its one thousand mile frontier with Malaysia. Having removed much of the anti-submarine equipment to lighten the aircraft, during the campaign in Borneo the Wessex was typically operated as a transport helicopter, capable of ferrying up to 16 troops or a 4,000 pound payload of supplies directly to the front lines.
Around 55 Westland Wessex HU.5s participated in the Falklands War, fighting in the South Atlantic in 1982. Their prime role was the landing, and moving forward, of Rapier missile systems, fuel, artillery and ammunition, in addition to being heavily used for the transportation and insertion of British Special Forces. A total of nine Wessex were lost during the Falklands campaign.
Civilian operations - A civilian version of the helicopter, the Wessex 60, was supplied to a number of civilian operators, and flew them from various UK airfields and helicopter pads to support the growing North Sea Oil industry until they were withdrawn in 1982.
In addition to Australia, the United Kingdom, the Royal Air Force operated twelve squadrons, flights and units and the Royal Navy flew seventeen squadrons. Other nations to fly the Westland Wessex were Brunei, Ghana, Iraq, Oman, and Uruguay.
In April 1961, the Royal Australian Navy announced its intention to purchase 27 Westland Wessex HAS31, (and later the updated HAS31B) helicopters to fly from their ships for anti-submarine patrols, casualty evacuations, and fleet communications duties.
The RAN accepted the first two in September 1963. The Wessex, and its dunking sonar array, quickly proved to be the most effective anti-submarine platform as yet seen in the RAN.
While the Wessex proved to be too large to reasonably operate from most of the RAN's destroyers and frigates, it was found to be well suited as a troop-transport helicopter from heavy landing ships and larger vessels.
The Wessex signalled a major operational shift for the Fleet Air Arm, enabling the RAN to proceed with the conversion of HMAS Melbourne as an anti-submarine platform.
In typical carrier operations, a Wessex would be deployed during the launch and recovery of fixed-wing aircraft as a guard helicopter; while during anti-submarine patrols, the routine procedure was to have one Wessex airborne to actively screen the ship while a second would be fully armed and prepared for offensive operations. Such an arrangement was used during troop transport deployments to Vietnam during the 1960ís.
Performing Search and Rescue sorties became another valued role of the Wessex; in 1974, multiple Wessex helicopters participated in the relief effort in Darwin in the aftermath of Cyclone Tracy.
By 1980, the Wessex was no longer being used for anti-submarine operations, having been replaced by the more advanced and capable Westland Sea King in this capacity. Instead, remaining Wessex helicopters were retained to perform its secondary roles as a plane guards, search and rescue platforms, and as a utility transport helicopter.
Royal Australian Navy maintained four squadrons, 723 Squadron, 725 Squadron, 816 Squadron, 817 Squadron and 723 Squadron.