XB-70 Valkyrie - The Mach 3 bomber

The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep penetration bomber for the United States Air Force&Strategic Air Command. Designed in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly at beyond Mach 3 at an altitude of 70,000 ft (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time. Two XB-70 prototypes were built for the U.S. Air Force. The aircraft program&high development costs, and changes in the technological environment with the introduction of effective high-altitude anti-aircraft missiles, led to the cancellation of the B-70 program in 1961. Although the proposed fleet of operational B-70 bombers was never built, the XB-70A aircraft were used in supersonic test flights from 1964 to 1969, performing research for the design of large supersonic aircraft. One prototype crashed following a midair collision in 1966; the other is on display...