In late 1959, Boeing began development of a manned reusable space plane, the X-20 Dyna-Soar (Dynamic Soaring). It was to be placed into orbit by a Titan III booster and constructed of several new, exotic alloys. Dyna-Soar's first orbital flight was scheduled for early 1965, but it didn't happen. Despite a cadre of astronauts in training and an excellent government review of the program and inspection of the full-scale engineering mockup, the U.S. military canceled the Dyna-Soar program in December 1963 because it had no viable military mission and was too expensive for a research vehicle. The partially completed prototype and the mockup were scrapped, as well as initial tooling set up for a production line for 10 space planes. It would be another 18 years before a first-generation space plane would be flying: the Space Shuttle, which first flew in April 1981.