The first S-55s received by the Royal Navy in 1950 were built by Sikorsky, but Westland acquired a license in 1950 and the first British-made S-55 flew at Yeovil in November 1952. Like the American models, the first Whirlwinds had Pratt & Whitney engines and were delivered to No.705 Squadron based at Gosport.

The RAF also ordered this helicopter for transport and rescue missions: the Whirlwind HAR Mk.2 (the same as the naval version except for some differences in equipment) joined the Transport and Coastal Command Units from 1955. With Wright R.1300 engines, the Whirlwind Mk.3 went into production for the Royal Navy in 1953 and operated for many years from both ship and shore bases. The subsequent RAF HAR Mk.4 version was modified for use in the tropics and fitted with a new variant of the Pratt & Whitney R-1340. It was used in Malaysia.

When Westland began producing the S-55, it specified that the American engine would be used until a more suitable British powerplant was available. To meet this requirement, Alvis developed a double radial called the Leonides Major, which delivered 882hp derated to 750hp. The re-engined Whirlwind flew in 1955. It was followed in 1956 by the Mk.7 version intended to replace the old Fairey Gannet antisubmarine aircraft.

Meanwhile, Westland had thought of adapting a turbine engine for the Whirlwind. The aircraft was first given a General Electric T.58 and then the more powerful D.H. Gnome turbine. The turbine-powered Whirlwind Series 3 flew in February 1959 and introduced a new nose profile which offered better visibility from the cockpit than the piston engine version. The Whirlwind could carry ten men or six stretchers, or a comparable load.

The RAF adopted the Whirlwind Mk.10 version in April 1960. More than 400 Whirlwinds were built, of which nearly 100 were exported to the following countries: Austria, Brazil, Canada, Cuba, France, Ghana, Jordan, Iran, Kuwait, Spain, Saudi Arabia and Yugoslavia.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

Westland obtained the licence to build the S-55 from Sikorsky in November 1950. The Series 1 and 2, powered respectively by a Pratt & Whitney R-1340 or Wright R-1300 engine or the 755hp Alvis Leonides Major 755, were used for both civil and military work.

The turbine-powered S-55 made its first flight as the Whirlwind Series 3 in February 1959, powered by a General Electric T58. At the end of the year a Series 3 flew with a 1050shp Bristol Siddeley Gnorne free-turbine - the licence-built version of the T58.

Like the S-55, the Series 3 has a single door on the left side. The pilot and co-pilot sit above and behind the engine which places their cabin directly under the centreline of the main rotor. The rotor is hydraulically operated for both cyclic and collective pitch controls. Forward vision for landing was not ideal in earlier versions of the Whirlwind since the engine housing was in the nose. The turbine version was better since, though the nose was longer, it was at a more raked angle. Unlike the US turbine-powered S-55, the Whirlwind Series 3 has its engine exhaust on the left side almost immediately above the forward wheel, which can make cargo loading slightly hazardous if the engine is running or the exhaust hot. The turbine engine can be retrofitted to Series 1 and 2 machines.

The Whirlwind can carry up to ten passengers, six stretchers or a freight load. The Series 2 machines in service with BEA were fitted with floats as well as wheels for use off inland waterways. Few Whirlwinds are in civil use in the 1980s.

Bill Gunston "The Illustrated Encyclopedia of Commercial Aircraft", 1980

- Westland built a total of 364 S-55s under licence between 1953 and 1966, including 68 WS-55 civil aircraft.

- Bristow Helicopters' Series 1s were used for 'flying crane' and oil rig support duties.

- British airline BEA used WS-55s between central London and Heathrow airport.

- Most turbine-powered WS-55 Series 3s were converted from piston-engined Series 1s and 2s.

- WS-55s were used from the 1950s in the Falkland Islands for whaling operations.

- In 1955 a Whirlwind on delivery was flown 5000km to the Persian Gulf.