Designed by North American Aviation in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly Mach 3+ at an altitude of 70,000 feet (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.The introduction of effective high-altitude surface-to-air missiles (SAMs), the program's high development costs, and changes in the technological environment with the introduction of intercontinental ballistic missile (ICBMs) led to the cancellation of the B-70 program in 1961.
Although the proposed fleet of operational B-70 bombers was canceled, two prototype aircraft were built as the XB-70A and used in supersonic test flights from 1964 to 1969. One prototype crashed following a midair collision in 1966; the other is on display at the National Museum of the United States Air Force in Ohio.
