This is the North American Aviation XB-70 Valkyrie gigantic supersonic strategic nuclear bomber, that never entered service.
There were only two prototypes built of the XB-70 Valkyrie, before the project was cancelled.
The supersonic bomber powered by six engines, could fly at Mach 3+, at 70,000 feet and could penetrate deeply into Soviet territory.
The North American Aviation was the prototype of the B-70 nuclear-armed, deep-penetration strategic bomber for the Strategic Air Command of the U.S. Air Force. In the 1950s, the North American Aviation company designed the Valkyrie bomber as a large, six-engine aircraft capable of reaching Mach 3+ while flying at 70,000 feet (21,000 m); these speed and altitude capabilities would allow the evasion of interceptor aircraft, the only effective weapon against bomber aircraft at the time.
In 1961, improved, high-altitude surface-to-air missiles (SAMs), the U.S. Air Force’s doctrinal change to low-level penetration bombing, the large development costs of the B-70 program, and the introduction of intercontinental ballistic missiles (ICBMs) to the U.S. nuclear arsenal, led to the cancellation of the B-70 program. As such, two prototype aircraft were built, and designated XB-70A; these aircraft were used for supersonic test-flights during 1964–69. In 1966, one prototype crashed after colliding in midair with a smaller jet aircraft; the remaining Valkyrie bomber is in the National Museum of the United States Air Force, in Ohio.