During the 1990s two SR-71 Blackbird aircraft were used by NASA as testbeds for high-speed and high-altitude aeronautical research at Dryden. The SR-71 was designed by a team of Lockheed personnel led by Clarence "Kelly" Johnson, then vice president of Lockheed's Advanced Development Company Projects. The SR-71 completed its first flight on December 22, 1964. More than a decade after their retirement the Blackbirds remain the world's fastest and highest-flying production aircraft ever built. The Blackbirds were designed to cruise at Mach 3.2, just over three times the speed of sound or more than 2,200 miles per hour and at altitudes up to 85,000 feet. The extreme operating environment in which they flew made the aircraft excellent platforms for conducting research and experiments in a variety of disciplines: aerodynamics, propulsion, structures, thermal protection materials, high-speed and high-temperature instrumentation, atmospheric studies, and sonic boom characterization. NASA photo, circa 1990s.