Designed and constructed during the "Cold War", the Valkyrie first flew in 1964. The United States issued a requirement for a heavy bomber capable of cruising at Mach 3 with range enough to reach the USSR to deliver a nuclear weapon. Rapid progress of intercontinental ballistic missile programs soon negated the role for which the Valkyrie was intended and the program was cancelled. Two prototypes were constructed however, the number two ship was lost in a tragic accident in 1966 when a chase plane collided with it during a test flight. The first airplane continued to fly with NASA until her retirement in 1969 and is now on display at the National Museum of the US Air Force near Dayton, OH.