The 1970s STOL Prototype Duel The US Air Force Canceled Then Quietly Turned Into The C-17

The U.S. Air Force’s 1976 Advanced Medium STOL Transport (AMST) program produced no direct replacement for the Lockheed C-130 Hercules, but it quietly seeded the C-17 Globemaster III. During AMST trials, the YC-15 used externally blown flaps to maximize thrust from its four engines and demonstrated strong short takeoff and landing performance. While AMST was canceled without buying the YC-15 or Boeing’s competing YC-14, McDonnell Douglas used prototype data when the Air Force later pursued a replacement for the C-141 Starlifter under the C-X program. The C-17, selected in 1981, delivered intercontinental airlift with scaled-up STOL engineering and better runway flexibility.