The Advanced Medium STOL Transport (AMST) project was intended to replace the Lockheed C-130 Hercules tactical transport in United States Air Force service with a new aircraft with improved STOL performance. Increased need for strategic airlift led the Air Force to cancel the AMST program and seek a larger airlifter. Under the C-X program, the YC-15's basic design would become the successful McDonnell Douglas (later Boeing) C-17 Globemaster III.