The Westland Whirlwind started life as the Sikorsky S-55, a machine developed in response to a United States military requirement for a large general-purpose helicopter. An associated contract was awarded to Sikorsky in 1948 and the first prototype flew in late 1949. The S-55 saw widespread service with the US Army, Navy, Air Force and Marine Corps with a total of 1281 being built.
The British company, Westland, produced 400 S-55s under licence as the Whirlwind. Some 100 were exported to other countries with the majority of the remainder destined for military use in the Royal Navy and RAF, with a few going to the Army and others employed in civil aviation. Powered by the Pratt & Whitney Wasp engine, the prototype British machine, the Westland HAR1, flew for the first time in August 1953 and entered service shortly thereafter. The later HAR3 was fitted with a larger Wright Cyclone engine whilst, from 1955, the HAR5 and subsequent models were powered by the British Alvis Leonides Major. Subsequently, some 70 HAR10s entered service with the Rolls Royce Gnome gas turbine; this engine was lighter and more powerful than the piston engines it superseded and offered significantly improved performance and reliability.
The Whirlwind had a crew of 2 or 3 depending on the role and seating in the main cabin for up to 10 passengers. It could also be configured as a freighter and was capable of carrying an external swing load. Whilst the aircraft served primarily in the air sea rescue and communications roles, the Royal Navy’s HAS7 became the first British helicopter designed for anti-submarine operations when it entered service in 1956. This version was equipped with radar and could carry either dipping ASDIC for submarine detection, a homing torpedo or depth charges. For the RAF, the HAR10 was so successful that it remained in service for 21 years, the last squadron converting to the Wessex in 1982.