The North American X-15 was a rocket-powered hypersonic research aircraft developed by North American Aviation for a joint NASA, U.S. Air Force, and U.S. Navy program. NASA describes the X-15 program as a nearly decade-long effort that investigated piloted hypersonic flight, reached unofficial records of Mach 6.7 and 354,200 feet, and produced data later used across Mercury, Gemini, Apollo, and Space Shuttle development.