The Westland Whirlwind helicopter was a British licence-built version of the U.S. Sikorsky S-55/H-19 Chickasaw. It primarily served with the Royal Navy's Fleet Air Arm in anti-submarine and search and rescue roles. It was also exported to other countries, and the Whirlwind was succeeded by the turbine powered Westland Wessex which was developed from the H-19/Whirlwind. The helicopter was made in many variants using a variety of radial (piston) and turbine engines.

The Sikorsky H-19 Chickasaw is a multi-purpose piston engined helicopter that was used by the United States Army and United States Air Force. It was also license-built by Westland Aircraft as the Westland Whirlwind in the United Kingdom. United States Navy and United States Coast Guard models were designated HO4S, while those of the U.S. Marine Corps were designated HRS. In 1962, the U.S. Navy, U.S. Coast Guard and U.S. Marine Corps versions were all redesignated as H-19s like their U.S. Army and U.S. Air Force counterparts.