The legendary XB-70 cruised at greater than Mach 3 at 75,000 feet (22,800 meters)-powerful performance for the 1960s. The dream began on Dec. 23, 1956, with a $360 million development contract award to NAA to begin work on three prototypes. Powered by six General Electric YJ93-GE-3 engines, the bomber rode on its own shockwave, an acclaimed aerodynamic advance.