Development

Developed by Igor Sikorsky from his famous VS-300 experimental helicopter, the R-4 became the world's first production helicopter, and the U.S. Army Air Force's first service helicopter.  The VS-316 was designated the XR-4, under the United States Army Air Forces' series for "Rotorcraft". The XR-4 made its initial flight on 13 January 1942 and was accepted by the Army on 30 May 1942. The XR-4 exceeded all the previous helicopter endurance, altitude and airspeed records that had been set before it. The XR-4 completed a 761-mile (1,225 km) cross country flight from Connecticut to Wright Field, Ohio, set a service ceiling of 12,000 feet (3,700 m), 100 flight hours without a major incident, and an airspeed approaching 90 mph (140 km/h).

The British Admiralty having learned of the VS-300, made a ship available that had been intended to show the USN their work with autogyros and ship operations. The Empire Mersey was fitted with a landing platform. After her loss in 1942 to a U-boat, she was replaced by the SS Daghestan. The British would receive two of the first eight helicopters built.

On 5 January 1943, the United States Army Air Forces ordered 29 prototypes. The first three prototypes were designated as the YR-4A and used for evaluation testing. The YR-4A benefited from a larger, 180 hp (130 kW) Warner Super Scarab (R-550-1) engine, compared to the 165 hp (123 kW) R-500-3 engine in the prototype, and a rotor diameter increased by one foot (30 cm). Evaluation of the YR-4A demonstrated a need for further improvements, including moving the tailwheel further towards the rear of the tailboom, venting the exhaust to the side instead of downward, and increasing the fuel capacity by five gallons (19 liters). These and other design changes led to the designation of later prototypes as YR-4B, which were used for service testing and flight training.

Operational history

On 22–23 April 1944, U.S. Army Lieutenant Carter Harman of the 1st Air Commando Group conducted the first combat rescue by helicopter using a YR-4B in the China-Burma-India theater.  Despite the high altitude, humidity, and capacity for only a single passenger, Harman rescued a downed liaison aircraft pilot and his three British soldier passengers; two at a time.  On 22–23 January 1945, another rescue by the R-4 involved several legs for refueling and navigating through passes between mountains nearly 10,000 feet (3,000 m) tall, to reach a weather station located at an elevation of 4,700 feet (1,400 m). The higher than normal altitude required a downhill run of 20 ft (6.1 m) to get airborne.

While the R-4 was being used for rescues in Burma and China, it was also being used to ferry parts between floating Aviation Repair Units in the South Pacific. On 23 May 1944, six ships set sail with two R-4s on board each vessel. The ships had been configured as floating repair depots for damaged Army Air Forces aircraft in the South Pacific. When the helicopters were not being used to fly the parts from one location to another, they were enlisted for medical evacuation and other mercy missions.

In Royal Air Force service, the R-4 was called the Hoverfly. The Helicopter Training School, formed January 1945, at RAF Andover, was the first British military unit to be equipped with the helicopter. Many of the RAF Hoverfly Is were transferred to the Royal Navy for training and one was used in 1945/46 by Fairey Aviation to develop rotor systems for their Gyrodyne helicopter.