For educational purposes<br /><br />The North American Aviation XB-70 Valkyrie is the prototype of the B-70 nuclear-armed, deep-penetration strategic bomber for the U.S. Air Force's Strategic Air Command. <br /><br />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).<br /><br />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. <br /><br />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. <br /><br />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.<br /><br />The introduction of the first Soviet surface-to-air missiles in the late 1950s put the near-invulnerability of the B-70 in doubt. <br /><br />In response, the US Air Force began flying its missions at low level, where the missile radar's line of sight was limited by local terrain, in this low-level penetration role, the B-70 offered little additional performance over the B-52 it was meant to replace. <br /><br />It was, however, far more expensive and had shorter range. Other alternate missions were proposed, but these were of limited scope. <br /><br />As the strategic role passed from bombers to intercontinental ballistic missiles (ICBMs) during the late 1950s, manned bombers were increasingly seen as obsolete.<br /><br />The USAF eventually gave up fighting for its production, and the B-70 program was canceled in 1961. <br /><br />Development was then turned over to a research program to study the effects of long-duration high-speed flight, as such, two prototype aircraft were built, and designated XB-70A; these aircraft were used for supersonic test-flights during 1964–69. <br /><br />In 1966, one prototype crashed after colliding in mid-air with a smaller jet aircraft; the remaining Valkyrie bomber is in the National Museum of the United States Air Force near Dayton, Ohio.
