| North American Aviation's B-70 Valkyrie was a nuclear-armed bomber designed for the United States Air Force's Strategic Air Command in the 1950s. The Valkyrie was a large six engine aircraft able to fly at Mach 3 at high altitudes, which would have allowed it to avoid defending interceptors, the only effective anti-bomber weapon at the time. The proposed cost of the aircraft, along with changes in the technological environment due to the introduction of the first effective anti-aircraft missiles led to the cancellation of the program in 1961. Although the proposed full fleet of operational B-70 bombers was never built, two prototype XB-70s flew in flight tests in the 1960s, performing research on the design of large supersonic aircraft. One prototype crashed following a midair collision in 1966, and the other is now on display at the National Museum of the United States Air Force in Dayton, Ohio. The development of the Valkyrie, along with the U-2 and SR-71 reconnaissance aircraft caused the Soviet Union to create the MiG-25 'Foxbat',[2] and new, improved surface to air missiles (SAMs), to counter them. | 
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