The Sikorsky R-4 was the world's first production helicopter and the U.S. Army Air Corp's first service helicopter. The original military model, the XR-4, was developed from the famous experimental VS-300 helicopter, invented by Igor Sikorsky and publicly demonstrated in 1940.
The Army R-4 was Sikorsky Model S-47, with a fabric covered tubular steel fuselage. Model variants ranged from A through C. The YR-4B was a two-place side-by-side, observation, reconnaissance, and MedEvac helicopter, with one external litter rack. Other R-4s were fitted with twin pontoons for use aboard ships or over water.
The XR-4 made its initial flight on 13 January 1942, and as a result of its successful flight tests, the USAAF ordered three YR-4As and 27 YR-4Bs for service testing and flight training. Of these 30, one went to Burma and one to Alaska, while several others were assigned to the U.S. Navy, U.S. Coast Guard and British Royal Navy. They showed such promise that the USAAF ordered 100 R-4Bs. It was also procured by the British under the name Hoverfly MK I and by the U.S. Navy as the HNS-1. It was tested extensively by the Coast Guard who later procured follow-on Sikorsky models.
In Burma, the first helicopter MedEvac rescue took place in April 1944 and the R-4 was first used in combat in May 1944. In a letter to a friend, Col. Philip G. Cochran, commanding officer of the 1st Air Commando Group, wrote "Today the 'egg-beater' went into action and the damn thing acted like it had good sense." In U.S. Navy testing, the R-4 became the first helicopter to land on a ship.