The YF-12 was a prototype interceptor aircraft developed by Lockheed's Skunk Works division for the United States Air Force (USAF) in the 1960s.
It was a twin-seat version of the famous SR-71 Blackbird reconnaissance aircraft, and was intended to serve as a high-altitude interceptor to defend against Soviet bombers.
The YF-12 was equipped with advanced radar and missile systems and could fly at speeds exceeding Mach 3.
The YF-12 set several speed and altitude records during its test flights, but the program was ultimately cancelled due to budget constraints and a shift in priorities towards air-to-ground missiles.
Only three YF-12s were built, and one of them is now on display at the Smithsonian National Air and Space Museum in Washington, D.C.