North American Aviation
NAA XB-70 Valkyrie

The North American Aviation XB-70 Valkyrie is a retired prototype version of the planned B-70 nuclear-armed, deep-penetration supersonic strategic bomber for the United States Air Force Strategic Air Command. Designed in the late 1950s by North American Aviation (NAA) to replace the aging B-52 Stratofortress and B-58 Hustler, the six-engined, delta-winged Valkyrie could cruise for thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m).

The B-70 was planned to use a high-speed, high-altitude bombing approach that followed a trend of bombers flying progressively faster and higher since the start of crewed bomber use. Through that same period, only two weapons proved effective against bombers: fighter aircraft and anti-aircraft artillery (AAA). Flying higher and faster made it more difficult for both; higher speeds allowed the bomber to fly out of range of the weapons more quickly, while higher altitudes increased the time needed for fighters to climb to the bombers, and greatly increased the size of the AAA weapons needed to reach those altitudes

Downsizing, upswing, cancellation

Then interest increased due to the politics of presidential campaign of 1960. A central plank of John F. Kennedy's campaign was that Eisenhower and the Republicans were weak on defense, and pointed to the B-70 as an example. He told a San Diego audience near NAA facilities, "I endorse wholeheartedly the B-70 manned aircraft." Kennedy also made similar campaign claims regarding other aircraft: near the Seattle Boeing plant he affirmed the need for B-52s and in Fort Worth he praised the B-58.