11 May 1964 – In a small city high in the California desert, the first prototype North American Aviation XB-70A-1-NA Valkyrie, 62-0001, rolls out of the hangar.
The XB-70 was the prototype version of the planned B-70 nuclear-armed, deep-penetration strategic bomber for the United States Air Force Strategic Air Command. The six-engined Valkyrie was capable of cruising for thousands of miles at Mach 3+ while flying at 70,000 feet and had been designed in the late 1950s by North American Aviation (NAA). It was planned to use high-speed, high-altitude bombing following the trend of bombers trying to fly faster and higher.
Flying at these speeds was expected to render the XB-70 immune to interceptor aircraft but the introduction of Soviet surface to ground missiles in the late 1950s put the invulnerability of the aircraft in doubt.
The USAF gave up on the production of the XB-70 and turned the plans for the aircraft over to research for studies on supersonic Flight. Two prototype XB-70A were built and used for tests from 1964-1969. In 1966 a Valkyrie crashed with a smaller airplane while flying in a tight formation. The only remaining Valkyrie bomber is in the National Museum of the United States Air Force near Dayton, Ohio.
Sources: Wikipedia, This Day in Aviation History by Bryan R. Swopes.