The North American XB-70 Valkyrie was the largest and fastest bomber ever built by the United States, but the massive six-engine Mach 3.0-capable jet never entered production. Only one surviving prototype sits in a museum in Dayton, Ohio, even as the Boeing B-52 it was supposed to one day replace continues to soldier on.
The idea behind the XB-70 originated in the 1950s when it was assumed ever-greater speeds and altitudes would enable American bombers to survive against Soviet air defenses unmolested on their way to delivering their doomsday payloads. At the time, the only effective defense against bombers were fighters and antiaircraft artillery. Even then, anti-aircraft guns were only marginally effective and interceptors were increasingly challenged by ever improving bomber performance.
However, with the advent of surface-to-air missiles (SAM), that began to change—the balance started to tip in favor of the defender. While the U.S. Air Force was aware of Soviet advances in SAM technology, the Pentagon didn’t start to understand the scope of the problem until Francis Gary Powers’ Lockheed U-2 spy plane was shot down while overflying the Soviet Union on May 1, 1960. But development of the XB-70 continued nonetheless.
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