The incredible Valkyrie was envisioned as a long-range, high-altitude, triple-sonic bomber, capable of Mach 3 at 74,000 feet. Conceived during the Cold War, just two prototypes were ever completed. One crashed during flight testing, the other survives as a centerpiece exhibit at the USAF Museum in Dayton, Ohio. This is the inside story of the development, testing, and cancellation of the revolutionary XB-70 Valkyrie.