At Mach 3, you travel about 3,000 feet per second. That's over half a mile (or 10 football fields). And at 70,000 feet, you're twice as high as the average airliner. Only a handful of aircraft have been capable of both feats, and fewer could cruise comfortably at both for several thousand miles.
Most were stealthy reconnaissance aircraft or engine-and-a-cockpit interceptors. The North American XB-70 Valkyrie was neither: It was a huge strategic bomber capable of carrying thousands of pounds of nuclear weapons at supersonic speeds. It first flew in 1964, faster than nearly every other aircraft before or since. It was also one of the largest and heaviest planes made, and it was obsolete before it even took flight.
Here's the story of the incredible, and nearly forgotten, supersonic superbomber.
An Up-Close Look at America's Forgotten Supersonic BomberSee all photos
Pushing the envelope
At the start of the Cold War, the prevailing thought was that aircraft needed to fly higher and faster to evade enemy aircraft. Outrun them and fly higher, it was thought, and you're essentially invincible. The Valkyrie comes from my favorite era in aviation, when bonkers design after bonkers design not only made it off the drawing board but to production.
The Air Force wanted a plane that combined the payload of its then-new B-52 Stratofortress with the supersonic speed of the B-58 Hustler. North American Aviation's proposal was the XB-70, which was later named the Valkyrie, following an Air Force contest. The designers pushed the limits of technology to create an aircraft that flew higher and faster than any plane its size had ever achieved before. Six huge General Electric YJ93 turbojet engines delivered 28,800 pounds of thrust each and used afterburners. Though highly inefficient at creating thrust at low speed, at Mach 3 afterburners are one of the most efficient ways to do a supersonic cruise. The fuel itself was used for cooling, something seen on the later (and faster) SR-71 Blackbird.
The delta wings, an excellent design for reaching supersonic speeds, would have adjustable wingtips. Along with a clever wedge air intake and other design elements, they'd allow the XB-70 to "sit" on its own shockwave, reducing drag and delivering lift. It used lightweight and strong cutting-edge materials like titanium and brazed stainless steel honeycombs.
With a top speed of Mach 3 and a cruising altitude of more than 70,000 feet, the XB-70 was designed to be too fast and too high for any Soviet aircraft to intercept. The Valkyrie also spurred engineers to envision a remarkable XB-70-influenced future. Ideas included using it as a high-speed orbital launch platform, as a mothership for other aircraft and even as a supersonic transport. With a proposed 80 to 107 passengers and a 4,000-mile range, it would carry about as many passengers as the Concorde yet was nearly twice as fast.
Nemesis of the Valkyrie
In the end, it wasn't the threat of any aircraft that ended the XB-70 program. By the Valkyrie's 1964 first flight, the Soviet Union had been building its S-75 Dvina surface-to-air missile system for seven years. It more than matched the XB-70's speed and altitude performance.
Even at home, a growing number of military brass knew the future wasn't in long-range manned bombers but intercontinental ballistic missiles, or ICBMs. Though the first generation of Titan and Atlas missiles had significant issues as reliable nuclear deterrents, their successors were improved. By the time the XB-70 had flown, both Titan II and Atlas were well on their way to becoming dependable launch vehicles for both military and civilian use. They'd continue in those roles for decades. The need for an expensive supersonic bomber to fly long-range missions into the USSR had become a thing of the past.
President John F. Kennedy canceled the program as a defense project in 1961, but that wasn't the end of the Valkyrie. NASA needed a large supersonic aircraft to test ideas for a potential American supersonic transport to compete against Concorde and the Soviet Tu-144. The space agency tested the first XB-70 built and helped North American make changes to the second aircraft, which was more stable and better capable at high speed. The data collected proved useful, though, ironically, it was used in helping to cancel the American SST program.
This second Valkyrie did the majority of the Mach 3 fights, but, sadly, it was involved in a tragic midair collision. During a 1966 photoshoot requested by GE, an F-104 Starfighter flown by NASA pilot Joe Walker got too close to the Valkyrie's right wingtip. It flipped the F-104 over the top of the bomber, taking out both of the XB-70's vertical stabilizers and killing Walker instantly. The Valkyrie flew for a few more seconds before entering an unrecoverable roll. Pilot Al White ejected and survived despite serious injuries; co-pilot Carl Cross wasn't able to eject and died.
Last flight of the Valkyrie
By the late '60s, the more cutting-edge YF-12 and SR-71 far outclassed the original XB-70, and both were far more useful as research aircraft. The loss of the second, more capable XB-70 further reduced its usefulness.
On Feb. 4, 1969, the first and only remaining XB-70 flew its last flight. It had logged just over 160 hours of flight time, very little of that at its much lauded top speed. From Edwards Air Force Base in California, it flew to Wright-Patterson AFB in Ohio and was towed on public roads to the National Museum of the US Air Force, where it is today.
The Research & Development Gallery at the National Museum of the Air Force has an incredible collection of rare and striking prototype aircraft, but all sit in the shadow of the Valkyrie. Literally. It's that big. The sharp angles look unlike anything from its day, or now. It's the future told by right angles and razor edges. The curves of the Lockheed YF-12A look positively retro in comparison.
Despite never firing a weapon in anger and flying for only five years, the Valkyrie provided hints of what was to come in aircraft design. Multiple companies copied, or were at least influenced by, the XB-70 in their entries for an American supersonic transport. You also can see echoes of the Valkyrie's shape in the B-1 Lancer, built by then-North American Rockwell. That aircraft is still in service.
In response to the XB-70's perceived threat, the Soviets developed one of the fastest interceptors ever: the MiG-25. Though it was highly flawed, its successor MiG-31 is still in service.
The XB-70 Valkyrie epitomizes early Cold War aviation. It was a wild design that pushed the limits of performance and technology. But despite its speed, it couldn't keep up with the times. Less impressive but more versatile designs from the era far outlived the XB-70 -- not least the B-52, which first flew in 1955 and will likely be in service in 2055.
But as a glimpse at that Jet Age future promised in the 1950s, it's incredible. Check out the gallery above for lots more photos of the Valkyrie then and now.
As well as covering TV and other display tech, Geoff does photo tours of cool museums and locations around the world, including nuclear submarines, massive aircraft carriers, medieval castles, epic 10,000 mile road trips and more. Check out Tech Treks for all his tours and adventures.
He wrote a bestselling sci-fi novel about city-size submarines, along with a sequel. You can follow his adventures on Instagram and on his YouTube channel.