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.
With the growing realization that Soviet SAMs posed an increasing threat to American bombers, the Pentagon started to explore low-level penetration as an alternative. Low-level penetration involved flying under the radar horizon using terrain to mask a bomber’s approach, which greatly reduces enemy response times. Moreover, the development of intercontinental ballistic missiles greatly reduced the United States’ reliance on manned bombers. Many leading military strategists of the time believed bombers were too vulnerable to survive the journey into Soviet airspace. As a result, President John F. Kennedy decided to cancel the XB-70 as a frontline bomber program on March 28, 1961.
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