Boeing C-137 Stratoliner procurement of the Boeing 707 was very limited, amounting to three Model 707-153s designated VC-137A. When delivered in 1959 these had four 13,500 lb (6123 kg) dry thrust Pratt & Whitney J57 (JT3C6) turbojets; when subsequently re-engined with 18,000 lbf (80.1 kN) dry thrust TF33-P-5 (JT3D) turbofans they were redesignated VC-137B. Only one other variant served with the USAF: this was the VC-137C "Air Force One" presidential transport, the two examples of which were Model 707-320B Intercontinentals with specialized interior furnishings and advanced communications equipment. Two further non-presidential C-137C aircraft were later added. To supplement its VC-137s, the USAF converted
Boeing VC-25 in general. The two aircraft often operate in conjunction with "Marine One" helicopters, which ferry the President to airports whenever a vehicle motorcade would be inappropriate. Two new aircraft, designated as VC-25B, are scheduled to be delivered by 2024. By 1985, the pair of Boeing 707-based VC-137s used as the Presidential aircraft had been in service for 23 and 13 years respectively, and the USAF began searching for an eventual replacement. The Request for Proposal issued stated that the aircraft to be selected should have at least three engines and an unrefueled range of at least . Both Boeing with