In the 1957 year, the U.S. Air Force accepted an offer from North American Aviation to replace the Boeing B-52 Stratofortress fleet with the ultra-fast North American XB-70 Valkyrie, capable of speeds of more than 3200 kilometers per hour.
Am joer 1957 hunn den devis vun der us-loftwaff vun der firma North american aviation park ersetzen boeing b-52 stratofortress op ultraschnelle North american xb-70 valkyrie, d ' kilometere vu méi wéi 3200 kilometer an der stonn.