US Air Force B-70 bomber

Answer 1

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 Mach 3+ at an altitude of 70,000 ft (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.

Source: Wikipedia

Additional answer: Note: The current photo above is not the B-70. The photo is of the B-58 Hustler, which was the earlier low-level high-speed penetration strategic bomber used by the US Air Force Strategic Air Command until the mid-1960's. The B-70 was of a similar design & flight profile to the commercial Concorde supersonic airliner. The B-70 never made it into production or service because the Soviets were successful in developing high altitude high-speed missile defenses. The Soviets also developed the MiG-25 Foxbat Mach 2.5 interceptor to counter the B-70.