December 7, 1941 The United States enters World War II.
January 14, 1942 Sikorsky XR-4 makes its first flight, testing proceeds rapidly.
April 20, 1942 First demonstration of XR-4 to military officials; it is declared ready for delivery.
May 17, 1942 XR-4 delivery flight to Wright Field after record 761-mile cross- country flight – first helicopter accepted by military.
August 17, 1942 Commander Army Air Forces, Gen. H. H. Arnold states he’s “willing to take a flyer” on helicopter program and pursue concurrent testing and production.
October 1942 XR-4 demonstrates use of General Electric hydrophones on Lake Erie to detect submarines.
January 22, 1943 USAAF orders 900 R-6As for liaison and rescue operations; Nash- Kelvinator to license build to allow Sikorsky to focus on R-5 production.
May 6-7, 1943 XR-4 demonstrates shipboard operations on the USS Bunker Hill; the Navy remained unconvinced, but the USAAF is satisfied that helicopters can safely operate from surface vessels and begins to employ the idea the following year.
May 26, 1943 USAAF contracts for 250 Sikorsky R-5As for Anti-Submarine Warfare/utility work, 100 Sikorsky R-4Bs or use as trainers
June 1, 1943 The Joint Aircraft Committee separates Sikorsky from Vought- Sikorsky at the request of the Navy to prevent helicopter production from interfering with Vought fighter production.
August 18, 1943 Sikorsky XR-5 makes its first flight, but is plagued by heavy vibration, and the R-5 program will go on to endure considerable engineering delays.
October 15, 1943 Sikorsky XR-6 makes its first flight.
Apr 23–May 4, 1944 Lt. Carter Harman evacuates 21 wounded and injured personnel in Burma with a Sikorsky YR-4B during a service test with the 1st Air Commando Group. This allows the USAAF to continue the ramping up of helicopter production and begin to commit helicopters into official tables of equipment of combat units. In addition to highlighting the promise of helicopters in unimproved regions, the experiment also showcases the limited durability and poor maintainability of 1st generation helicopters.
June 20, 1944 XR-1A delivered to Wright Field - two years behind schedule.
October 11, 1944 The USAAF’s 1st Aircraft Repair Unit (Floating) departs for Pacific – the first unit to deploy to a combat zone with helicopters as standard equipment.
September 6, 1944 The USAAF helicopter school at Freeman Field, Indiana opens.
December 1944 The USAAF helicopter school moves to Chanute Field, Illinois.
January 22, 1945 The 10th Air Force Air Jungle Rescue Unit receives a YR-4B from Wright Field for rescue operations in Burma and later performs the first special operations helicopter mission.
March 1945 The USAAF’s 162nd Liaison Squadron becomes the first unit equipped with R-6A helicopters.
April 20, 1945 The USAAF’s 8th Emergency Rescue Squadron arrives in Kunming, China with 5 YR-6As.
June 1945 The USAAF helicopter school moves to Sheppard Field, Texas.
June 16-29, 1945 R-4Bs and R-6As of the 5th and 6th Aircraft Repair Units (Floating) medevac 70 wounded soldiers from frontlines on Luzon.
August 16, 1945 Work on all military helicopters yet to enter production lines ceases.
World War II realized the development and employment of practical helicopters, saw the establishment of a viable helicopter industry and convinced the military and general public that this was a technology with future potential and was worthy of further investment. For the first time, the United States became the center of rotary wing development. In spite of a promising start, Germany failed to invest in the promising Focke and Flettner designs until it was too late. Great Britain also became convinced that the helicopter was a viable military platform, but lacked the excess industrial capacity and resources to support development, so it relied on U.S. lend-lease quantities of helicopters to support its requirements, which in turn strengthened the interest and investment in the fledgling U.S. helicopter industry. Autogiros enjoyed a brief resurgence of interest in the United States and even saw combat in the Soviet Union and Japan, but by 1944, the question of the superiority of the helicopter over the Autogiro in terms of capability and performance had been conclusively settled in favor of the former.
World War II marked the advent of the practical single main rotor helicopter with auxiliary anti-torque tail rotor. This configuration, refined by Sikorsky, has remained the most common configuration since this period. Many others have persisted, though often in the form of proprietary or operational niches. Other significant milestones included Arthur Young and Bartram Kelly’s successful implementation of the semi-rigid rotor for Bell Aircraft and Frank Piasecki’s tandem rotor. Germany’s developments at this time were largely evolutionary implementations of late 1930s designs, with the notable exception of Friedrich von Doblhoff’s innovative tip-jet designs.
Application and Operations
The predominant use of helicopters during WWII was in the evaluation of helicopters for military purposes. This general occurred off the battlefield, but sometimes in combat as well. The next largest use of helicopters was in training helicopter pilots for the intended numbers of operational helicopters in production in the latter half of the conflict. Logistical support and search and rescue constituted the primary in-theater contribution of helicopters. By the time of its surrender, Germany had begun integrating helicopters into one transport organization, but generally failed to accomplish any significant operational tasks with its helicopters outside of demonstrations, which though impressive, were hardly critical to the war effort. Most operational movements of German helicopters were to position them rather than to employ them. Great Britain utilized American built Sikorsky R-4s for evaluation, training and limited special assignments such as spotting for naval gunfire exercises.
The only regularized use of helicopters in combat zone occurred with the United States operating in the Pacific and in the China-Burma-India theaters. Beginning in April, 1944, the U.S. Army Air Forces began a service test in Burma with four Sikorsky YR-4Bs (another crashed in transit). Though one was soon lost in an accident and another two were cannibalized for parts, one of these YR-4Bs piloted by Lt. Carter Harman managed the first combat rescues of wounded or stranded personnel. Though only able to sustain operation before succumbing to parts issues, this service test validated helicopter use and allowed other deployments to proceed. In early 1945, another YR-4B arrived in Burma, this time to support the 10th Air Jungle Rescue Unit. It proved more successful than the other YR-4Bs deployed the previous year and logged numerous rescues and at least one special operations mission. In the fall and winter of 1944, 6 Liberty ships modified as floating repair depots deployed to the Pacific as Aircraft Repair Units (Floating). Each of these Army Air Forces vessels accommodated two helicopters (initially R-4s, but replaced later in some instances by R-6s), which were intended to ferry small components from ship to shore to support aircraft operating off of forward island bases that had not yet established an integral maintenance depot. These helicopters performed well in this role, though not without occasional loss due to accident, usually due to a lack of power. Among the more notable accomplishments by these helicopters was the rescue of approximately 70 wounded soldiers from the highlands of central Luzon in the Philippine Islands during late June, 1945. In spite of limited payloads and detrimental density-altitude conditions, the Sikorsky R-4B and YR-6As of the 5th and 6th ARU(F)s achieved their notable, but largely forgotten, rescues. In China, the 8th Emergency Rescue Squadron was the first forward deployed unit to have helicopters at the core of its allocated equipment. With its deployment in May 1945 of five R-6As, the squadron demonstrated that helicopters had a useful role in combat search and rescue of downed aircrews. The Army Air Forces was also forming Liaison Squadrons built around helicopters in preparation for the invasion of Japan.
Why did the U.S. deploy its helicopters to the Far East, but not to Europe? The answer is that Europe was reasonably suited to the light planes that could perform many of the same missions as helicopters, whereas the forbidding terrain of the CBI and the Pacific islands frequently eliminated even STOL-type light planes as a viable option. WWII demonstrated that the ability to hover was not merely an interesting stunt, as it had been earlier in the war, but it was a capability desperately desired by the military when operating in challenging environments.
Design and Manufacture
Though both Focke and Flettner were engaged in producing multiple examples of the same model helicopter before any other manufacturer, only Focke initiated mass production. Political delays and the allied bomber offensive delayed production until the very end of the war and Focke succeeded in fielding only one true production example of the Focke-Achgelis Fa 223. Contrary to post-war claims by Flettner that he had orders for 1,000 Fl 282s, undoubtedly intended to improve his postwar standing among the allies, he did not. The Flettner intermeshing design worked well from a performance standpoint, but was mechanically over-complex with a massive gearbox wholly unsuited to mass production. Its battlefield utility suffered greatly as the intermeshing design made it dangerous to approach and made its intended shipboard applications particularly hazardous. Its need to accommodate passengers in a space on the opposite side of the engine and transmission made it unsuitable for utility missions and it lacked the ability for internal or exterior carriage of cargo or stretchers. The Fa 223 was far better from a utilitarian standpoint, with the greatest internal capacity and useful load of any fielded helicopter of the period, but the lateral rotor arrangement was particularly problematic when hovering as wind and terrain conditions could cause roll instabilities to develop as they moved in and out of translation and ground effect.
In the United States, helicopter production caused strains on existing aircraft production facilities that were already overburdened with conventional combat aircraft orders. The U.S. Navy and Army Air Corps engaged in political football over helicopter production, because when the U.S. entered the war, Sikorsky, the only quantity manufacturer of helicopters in the country during the conflict, was part of Vought-Sikorsky, a division of United Aircraft, whose plant was under Navy cognizance and was slated for the manufacture of what would be the Vought F4U Corsair.