Military Hardware: Tanks, Bombers, Submarines and More At Mach 3.1 and 70,000 Feet, the XB-70 Valkyrie Bomber Could Outrun Every Russian Interceptor — but the U.S. Cancelled It In the late 1950s, the U.S. spent $800 million building a Mach 3.1 strategic bomber that could cruise above 70,000 feet and outrun every... Jack BuckbyMay 8, 2026