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XB-70 Valkyrie

3.1 Mach

The Valkyrie was a prototype long-range, high-speed bomber designed by North American Aviation in the late 50's. The XB-70's design called for a bomber capable of deploying nuclear payload deep into enemy lines while avoiding interceptors. Piloted by a crew of two, the Valkyrie was powered by six engines, capable of breaking Mach 3. The Valkyrie program was canceled in the 60's due to development of the more-practical ICBM. Unit cost: $750 million.