The Lockheed Blackbirds hold a unique place in the development of aeronautics . In their day , the A-12 , YF-12 , M-21 , D-21 , and SR-71 variants outperformed all other jet airplanes in terms of altitude and speed . Now retired , they remain the only production aircraft capable of sustained Mach 3 cruise and operational altitudes above 80,000 feet . In this paper the author describes the design evolution of the Blackbird from Lockheed 's early Archangel studies for the Central Intelligence Agency through Senior Crown , production of the Air Force 's SR-71 . He describes the construction and materials challenges faced by Lockheed , the Blackbird 's performance characteristics and capabilities , and the National Aeronautics and Space Administration 's role in using the aircraft as a flying laboratory to collect data on materials , structures , loads , heating , aerodynamics , and performance for high - speed aircraft .