TheNorth American Aviation XB-70 Valkyriewas the prototype version of the proposedB-70nuclear-armed deep-penetrationstrategic bomberfor theUnited States Air Force's (USAF)Strategic Air Command. Designed byNorth American Aviationin the late 1950s, the Valkyrie was a large six-engined aircraft able to flyMach3+ at an altitude of 70,000 feet (21,000m), which would have allowed it to avoidinterceptors, the only effective anti-bomber weapon at the time.

Improved high-altitudesurface-to-air missiles(SAMs), the change to low-level penetration bombing, the program's high development costs, and the introduction ofintercontinental 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 theXB-70Aand used in supersonic test flights from 1964 to 1969. One prototype crashed following a midair collision in 1966; the other is on display at theNational Museum of the United States Air Forcein Ohio.