erasing much of the XB-52’s speed advantage. But, the Air Force planners said, if Boeing could come up with an all-jet, long-range bomber.... That was on a Friday. Boeing’s team, led by ...

The XB-70 Valkyrie, a Mach 3-capable bomber developed during the Cold War, was designed to outpace Soviet air defenses. Powered by six turbojet engines, it could reach 2,076 mph at 73,000 feet.