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.

Westland Aircraft was a British aircraft manufacturer located in Yeovil, Somerset. Formed as a separate company by separation from Petters Limited just before the start of the Second World War, Westland had been building aircraft since 1915. During the war the company produced a number of generally unsuccessful designs, but their Lysander would serve as an important liaison aircraft with the Royal Air Force. After the war the company focused on helicopters, and was merged with several other British firms to create Westland Helicopters in 1961.