In 1964, the U.S. Air Force (USAF) sought a new bomber that could fly at supersonic speeds at high altitude and at high subsonic speeds at low altitude. However, then Secretary of Defense Robert McNamara found crewed bombers unnecessary as a nuclear deterrent. Moreover, the Vietnam War was ramping up, so McNamara limited the bomber project to studies and component development.
With a widening war, the strategic, fast, high-flying bomber project stalled in the 1960s, while the B-52—which excelled in a low-altitude role—remained relevant on bombing missions in Vietnam.
