• The Air Force’s XB-70 Valkyrie bomber was the fastest bomber ever developed.
  • The aircraft ran into development difficulties, powerful Soviet air defenses and sky-high costs, eventually forcing its cancelation.
  • The Air Force and North American Aviation, hoping to spur wider interest, came up with a variety of alternate uses for the XB-70, some of which were of questionable practicality.

In the early 1960s, the U.S. Air Force developed the XB-70, the largest, fastest bomber ever built. The ambitious airplane was eventually shot down not by enemy missiles, but advances in enemy air defenses and sky-high costs.

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Desperate to save the plane, the Air Force and contractor North American Aviation developed several alternate uses for the plane, including everything from launching intercontinental ballistic missiles (ICBMs) to space capsules.

a north american xb 70 valkyrie in flight
XB-70 prototype in flight, date unknown.
Universal History Archive//Getty Images

Named Valkyrie, after the female battle spirits of Norse mythology, the bomber was built to penetrate Soviet air defenses in a nuclear war and deliver thermonuclear bombs on targets. The XB-70 was 196 feet long, 31 feet tall at the tail, and had a maximum gross weight of 521,000 pounds.

The bomber tucked six General Electric J93-GE 3 turbojet engines into a wide, flat fuselage, giving the plane the ability to cruise at 2,000 miles per hour (Mach 3) at an altitude of 72,000 feet.

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The XB-70 was designed to fly high and fast, outracing enemy air defenses on the ground to hit targets across the Soviet Union. Unfortunately, advances in Soviet air defenses made the XB-70’s flight profile obsolete, while the Pentagon discovered the new, land-based ICBM could strike targets far more quickly and cheaply.

The XB-70 was also considered expensive, with each production bomber projected to cost an estimated $24.5 million, or $237 million today. The final production cost was significantly higher and likely sealed the Space Age bomber's fate.

xb 70a landing
XB-70 prototype landing.
Smith Collection/Gado//Getty Images

The XB-70 was canceled twice: once in 1959 by the Eisenhower administration and again in 1961 by the Kennedy administration. In the meantime, Air Force and North American engineers struggled to figure out ways to somehow keep the plane alive in an alternate role. A revolutionary plane with a fully pressurized cabin, plenty of interior room, and the ability to cruise at Mach 3 ought to be good for something ... right?

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Now, the Air Force Material Command History Office, located at Wright Patterson Air Force Base, has published a new 20-page paper outlining all of the crazy (and maybe not-so-crazy) ideas engineers had to recycle the XB-70. Download it here.

xb 70
XB-70 with X-20 Dyna-Soar and attached booster rockets.
U.S. Air Force

One of the most popular ideas for the XB-70’s post-military career was as the first stage for a space-launching system. The Valkyrie could fly to altitudes of up to 72,000 feet, negating the need for any rocket-based system to fly that distance. Several proposals saw a smaller rocket, space plane, or other space-launch system mated to the former bomber.

This included the Air Force’s proposed X-20 Dyna-Soar manned spaceplane, spy satellites, and even the Gemini space capsule. The latter was to be released from an internal payload bay, but the idea was completely impractical; at 72,000 feet, the XB-70 was far from space and still in Earth’s atmosphere.

b 52 carrying rocket plane
The X-15 Space Plane was typically launched from a B-52 bomber, as shown here, but it could have been carried by the XB-70.
Dean Conger//Getty Images

Another idea called for using the XB-70 as a hypersonic launch aircraft. The XB-70 was positioned as a launch vehicle for the North American X-15 spaceplane, a manned, rocket-powered aircraft that flew at Mach 6.7. Launched from an XB-70 mothership at Mach 3, the bomber's speed would've given the X-15 a useful boost.

Still, using a faster launch plane wouldn't have made the X-15 any faster, and the use of the expensive ex-bomber would likely have been an unnecessary expense.

The XB-70 was also pitched as a partner with the very system that made it obsolete: the ballistic missile. The Valkyrie was envisioned as carrying one large Minuteman II ICBM in an internal weapons bay, or two smaller Skybolt missiles.

Theoretically, this would've given the Air Force greater flexibility in wartime, launching an ICBM against the Soviet Union from a new and unexpected direction. But it was an awfully expensive way to launch just one or two missiles.

xb 70
U.S. Air Force

Finally, engineers tried to sell the the XB-70 in a most absurd configuration: as a military jetliner or ambulance.

The XB-70 could fit 80 passengers in airline-style seating, with the convenience of a “hot liquid buffet.” Alternately, it could transport 72 medical patients, plus attending nurses. It was even pitched as a cargo transport, with a hinged cabin allowing the loading of cargo pallets.

Needless to say, none of these ideas passed the cost-to-utility test, as the Valkyrie would've been the most expensive people-mover ever pressed into service.

Ultimately, there really wasn't any other mission suitable for the revolutionary XB-70. The airplane's excessive cost made practically every other mission prohibitively expensive, and today, the last prototype aircraft resides at the National Museum of the U.S. Air Force.

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Kyle Mizokami

Kyle Mizokami is a writer on defense and security issues and has been at Popular Mechanics since 2015. If it involves explosions or projectiles, he's generally in favor of it. Kyle’s articles have appeared at The Daily Beast, U.S. Naval Institute News, The Diplomat, Foreign Policy, Combat Aircraft Monthly, VICE News, and others. He lives in San Francisco.