The Lockheed SR-71 "Blackbird" is a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation.^{[N 1]} It was operated by the United States Air Force (USAF) and NASA.^[1]

The SR-71 was developed as a black project from the Lockheed A-12 reconnaissance aircraft during the 1960s by Lockheed's Skunk Works division. American aerospace engineer Clarence "Kelly" Johnson was responsible for many of the aircraft's innovative concepts. The shape of the SR-71 was based on that of the A-12, which was one of the first aircraft to be designed with a reduced radar cross-section. Initially, a bomber variant of the A-12 was requested by Curtis LeMay, before the program was focused solely on reconnaissance. Mission equipment for the reconnaissance role included signals intelligence sensors, side-looking airborne radar, and a camera;^[2] the SR-71 was both longer and heavier than the A-12, allowing it to hold more fuel as well as a two-seat cockpit. The SR-71 entered service in January 1966.

During aerial reconnaissance missions, the SR-71 operated at high speeds and altitudes (Mach 3.2 and 85,000 feet, 25,900 meters), allowing it to outrace or entirely avoid threats.^[2] If a surface-to-air missile launch was detected, the standard evasive action was simply to accelerate and outpace the missile.^[3] On average, each SR-71 could fly once per week due to the extended turnaround required after mission recovery. A total of 32 aircraft were built; 12 were lost in accidents with none lost to enemy action.^[4][5] During 1989, the USAF retired the SR-71 largely for political reasons; several were briefly reactivated during the 1990s before their second retirement in 1998. NASA was the final operator of the Blackbird, who used it as a research platform, and was retired in 1999.^[6] Since its retirement, the SR-71's role has been taken up by a combination of reconnaissance satellites and unmanned aerial vehicles (UAVs); a proposed UAV successor, the SR-72, is under development by Lockheed Martin, and scheduled to fly in 2025.^[7] The SR-71 has several nicknames, including "Blackbird" and "Habu".^[8] As of 2022 the SR-71 holds the world record it set in 1976 as the fastest air-breathing manned aircraft, previously held by the related Lockheed YF-12.^[9][10][11]