Xb70

The North American Aviation XB-70 Valkyrie was the prototype of the B-70 nuclear-armed, deep-penetration strategic bomber for the United States Air Force Strategic Air Command. In the late 1950s, North American Aviation designed the Valkyrie bomber as a large, six-engined aircraft capable of reaching Mach 3+ while flying at 70,000 feet (21,000 m). At these speeds, it was expected that the B-70 would be almost immune to interceptor aircraft, the only effective weapon against bomber aircraft at the time. The bomber would spend only a few minutes over a particular radar station, flying out of its range before the controllers could position their fighters in a suitable location for an interception. Its high speed also made the aircraft difficult to see on the radar displays and its high-altitude flight could not be matched by any contemporary Soviet fighter. Wikipedia