While the Saab 35 Draken may be the coolest, most futuristic combat jet ever made, when it comes to bombers that title goes to the XB-70 Valkyrie, a gigantic supersonic strategic nuclear bomber that never entered service. Seriously, when I say gigantic I really mean it. This thing is unbelievable—check the image below.
There were only two prototypes built of the North American Aviation XB-70 Valkyrie before the project—which wanted to create a nuclear bomber that could penetrate deeply into Soviet territory at supersonic speeds and very high altitude—was cancelled. Powered by six engines, the Valkyrie was that bomber: It could could fly at 70,000 feet at Mach 3+, which put it far from the reach Soviet fighter jets at the time.
But, as the critics of the time said—notably Kelly Johnson, one of the creators of the SR-71 Blackbird and the U-2 spy plane—it was dead even before it left the drawing boards in the mid-1950s (it's hard to believe that this amazing plane was designed just a decade after World War II ended, just like the SR-71.)
By 1961 the US Air Force knew that new high-altitude surface-to-air missiles could take down the XB-70, as demonstrated by the U-2 shot down in Soviet airspace on May 1, 1960. Then, the birth of the intercontinental ballistic missile—which could deliver the same or more destruction power faster and with no human risk whatsoever—was the final straw that killed this amazing bird.
There's only one of these prototypes left at the National Museum of the US Air Force in Dayton, Ohio. The other one was destroyed in a mid-air collision during a publicity photo shoot flight on June 8, 1966. Here are two photos taken just before the accident:
The photo below was taken just after the collision. The ball of fire is the F-104—the one with the orange tail above—that went under and touched the Valkyrie's right wing before flipping over and destroying the XB-70's vertical stabilizers and part of its left wing.
The XB-70 spun out of control shortly after that, crashing against the ground before the pilots could eject. This is the story of that accident: