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B-24 Tankers and B-17 Receivers
From the earliest days of aviation, the problem of range extension for aircraft was contemplated. Range extension would allow aircraft to transit large distances or bodies of water without the problem of landing for services. In a military application, it would allow the bomb-laden aircraft to take off with heavier weapons loads, and reach targets much further than normally possible. A solution to range extension, by air-refueling, surfaced very early in the history of aviation.
As told by William Wolf in his book Conquest of the Skies: Seeking Range, Endurance, and the Intercontinental Bomber, once America entered the war, the United States Army Air Corps (USAAC) initiated studies on an aerial refueling solution and three primary refueling concepts were deliberated by US air planners. The first was launching B-17 Flying Fortresses from Midway Island against Japan using modified B-24 Liberators as tankers; the second used B-24s from Hawaii with tanker support from Navy seaplanes; and the third used B-17s to tow fuel-laden gliders to serve as tankers.
But it would be Sir Alan Cobham’s prewar use of aerial refueling that was resurrected*. Washington looked to contact FRL, whose employees had dispersed, but RCAF Wing Commander Hugh Johnson, who was in charge of the tanker operations at Gander**, was located and assigned to the American project. While organizing the project it was discovered the FRL equipment left at Gander was all for tankers and none for receivers. Johnson was flown to Britain and collected the FRL equipment, drawings and several FRL technicians.
B-24s for the in-flight refueling of B-17s not viable
It was not until, June 1943 that in-flight refueling testing was begun using a B-24D tanker and a B-17E receiver at Eglin Field, Florida. Hugh Johnson was in command; Percy Allison, British Air Commission, was the technical adviser; Capt. Fred Bretcher and 1Lt. M. K. Norton were pilot and co-pilot, respectively, of the B-24D tanker; and Capt. Ralph C. Hoewing and 1Lt. John Kelting were pilot and co-pilot, respectively, of the B-17E receiver. Refueling was accomplished at 150 mph, and by the seventh refueling flight, the receiver’s tanks were filled to 101 percent and fuel was seen flowing out of its tank vents. It was found that loaded with three tons of bombs, the B-17’s radius was extended from 1,000 to 1,500 miles by refueling.
Although the tests were considered successful, the equipment for squadrons of B-24 tankers and B-17 receivers would have to be refined and manufactured by the country’s already over extended aircraft manufacturers, the tankers and receivers modified, and the crews trained. By summer 1943, B-29s were beginning to come into inventory and B-29 units were in training and expected to enter combat by early 1944. Since the B-29 carried more than twice the bomb load of a B-17 and had a round trip combat radius of 1,500 miles carrying twice the bomb load of the B-17, the costly effort to form squadrons of B-24s for the in-flight refueling of B-17s was no longer viable.
B-24 Tankers and other Receivers
In 1944, the Army Air Forces (AAF) initiated a study on the feasibility of equipping B-29s with an in-flight refueling capability. Wright Field determined it was possible to modify the bomber, but the B-24 tanker’s 1,500 gallon capacity only extended the B-29’s range by 830 miles and the project was abandoned.
The AAF also investigated a possible refueling method for smaller aircraft and engaged contractor All American Aviation to equip and test a specially modified P-38 Lightning and a B-24 tanker. In the test, the B-24 suspended an external fuel tank on a cable, with the P-38 maneuvering to catch the cable securing it into a device mounted on the forward fuselage. The twin-engine fighter was then to descend to the tank, which was to lodge into the securing device while the cable broke away. A nitrogen bottle discharged, forcing the fuel into the fighter before ejector springs released the tank. The tests were not at all successful, and in March 1945, the AAF canceled the method; thus, the AAF would not use air refueling operationally during WWII.
Notes
*Sir Alan Cobham believed that he could fulfil aviation’s full potential by developing and demonstrating in-flight refuelling. He understood that it takes more power for an aeroplane to take off than to fly. The additional power needed to take off results in a smaller range and payload for that aeroplane. Cobham established Flight Refuelling Limited (FRL) in 1934 to provide a solution for this problem. His company developed the pioneering ‘probe and drogue’ technique of in-flight refuelling which is still used today by air forces all over the world. Flight Refuelling Limited exists today as Cobham PLC, which continues to develop aviation technology (Source: Royal Air Force).
** FRL used two obsolete Handley Page HP.54 Harrow bombers as tankers — one at Gander, Newfoundland, and the other at Rineana, Ireland. These air refueling operations were not intended to extend the flight times, but to allow the flying boats to take off with minimal fuel and more mail. Imperial Airways flew 15 of these transatlantic missions before the outbreak of World War II (Source: U.S. Air Force).
Conquest of the Skies: Seeking Range, Endurance, and the Intercontinental Bomber is published by Schiffer Publishing and is available to order here.
Photo credit: U.S. Air Force
