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's 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, 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's high devel… (More on Xb-70)