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The XB-70 Valkyrie, a Mach 3 bomber designed for the U.S. Air Force, aimed to replace the B-52 but was ultimately canceled after a mid-air collision and changing military needs. Only two prototypes were built, with one destroyed in an accident.

The surviving Valkyrie contributed to aeronautical research until 1969 and is now displayed at the National Museum of the U.S. Air Force.