High Quality Content by WIKIPEDIA articles! The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep-penetration strategic bomber for the United States Air Force`s (USAF) Strategic Air Command. 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.