One of two prototype XB-70A Valkyries takes off on August 17, 1965 (NASA).

‘The XB-70 fulfilled General Curtis E. LeMay’s dream of a bomber that could penetrate the Soviet Union with impunity, carrying enough ordnance to decide the outcome of a war in a single strike’

The magnificent 500,000-pound Valkyrie could cruise at Mach 3. It had monumental firepower, wingtips that folded down to enhance its exotic lines, and—best of all—a shape that did the impossible: obtain something for nothing from the air. North American Aviation’s XB-70 fulfilled General Curtis E. LeMay’s dream of a bomber that could penetrate the Soviet Union with impunity, carrying enough ordnance to decide the outcome of a war in a single strike. To the public, the Valkyrie represented the epitome of American aeronautical genius, and so it was. Yet the XB-70 took years to conceive, design and build. It was fatally compromised by a declining defense budget and the advent of improved surface-to-air and intercontinental ballistic missiles.

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Today the legacy of the space age—from Sputnik to the International Space Station—has left the public somewhat jaded about avia­tion advances. Yet during the 15 years from the initial requirement to the XB-70A’s retirement, most Americans were still excited about new airplanes. With its striking, lethal beauty, the Valkyrie captured the public’s imagination like few other aircraft.

Considered by many the most extreme example of aircraft engineering to date, the XB-70A was in truth a simplified version of even more extravagant concepts. American aero­nautical engineers were tasked in 1954 with achieving General LeMay’s goal of a true strategic bomber. His call came when the Soviet Union was recognized as a genuine superpower that possessed nuclear weapons and subscribed to a first-strike policy. And LeMay knew that improvements in Soviet ra­dar and missile systems would raise the attrition rate for Boeing B-47 and B-52 bombers to an unacceptable level by the early 1960s.

LeMay charged the Air Force and the in­dustry with a dual task. They were to develop two weapon systems in parallel that would have some commonality in components, but using two entirely different types of power plants. Weapon System 125A was to be a nuclear-powered bomber, one that created an astounding story all its own before being canceled. Weapon System 110A was to use a more conventional power plant, possibly enhanced by high-energy chemical fuels.

At this point all the competing design firms believed that sustained supersonic flight used impractical amounts of fuel. Thus the specs for WS-110A called for a Mach 0.9 cruise to the combat zone, followed by as high speed a supersonic dash as possible, for as long as 1,000 to 2,000 miles. And while an altitude of 60,000 to 70,000 feet was desired, manufacturers were also told to investigate the possibility of low-level operations.

Boeing and North American both became contenders for the WS-110A prize. They de­veloped a series of highly varied designs, some with gross weights of 750,000 pounds. Both firms turned to a “floating wing panel” system originally advocated by German designer Richard Vogt. On one North American design, the 190,000-pound floating wing panels, roughly the size of a B-47, were to be drained of fuel in combat, then jettisoned, with the now smaller, cleaner element of the bomber capable of Mach 2. LeMay complained that it looked like a three-ship formation, not an airplane.

North American and Boeing came to believe the Air Force’s goals could be achieved by a smaller plane that flew at supersonic speed for the entire mission. Competing engine manufacturers—Allison, General Elec­tric and Pratt & Whitney—agreed. The Air Force then revised its specs, calling for a cruise speed of Mach 3 to Mach 3.2, capability of flying at 70,000 feet and a range of be­tween 6,000 and 10,000 miles.

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