Several schemes were tested for in-air refueling. One of the first Thunderjets used for air refueling tests was an EF-84E 49-2091 fitted with a probe at about 2/3 span on the leading edge of the left wing. The two schemes that proved to be most suitable in operation were the probe-and-drogue method, and the flying-boom system developed by Boeing. Some F-84E and G Thunderjets were fitted with probes in the wing-tip auxiliary tanks. Starting with Block 20, all F-84Gs were manufactured with fuel recepticles covered by retractable doors, to receive the Boeing boom, at the inner leading edge of the left wing.
F-84G from 309 FES refueling from KB-29. USAF Photo via Joe Vincent.
Another scheme was an aerial refuelling system that used fighter planes as tankers through the use of a "buddy" in-flight refuelling system. The buddy system incorporated a tank the same size and shape as a 450-gallon aircraft external fuel tank that was divided into two compartments, one containing fuel, the other the refuelling mechanism. Fuel was transferred from the tanker via a "drogue" to a "probe" in the leading edge of the receiving aircraft.
A Republic RF-84F Thunderflash photo-reconnaissance fighter in need of fuel approaches a Republic F-84F thunderstreak fighter-bomber equipped with a "buddy" refueling system tank. Republic photo via Jon Bunker.