In the 1950s, the United States Air Force toyed with the idea of creating a supersonic flying saucer called Project 1974. The creation, which could hypothetically "[reach speeds] between Mach 3 and Mach 4, a ceiling of over 100,000 ft. and a maximum range with allowances of about 1,000 nautical miles," was eventually cancelled in 1960 after prototypes had trouble reaching the desired "100,000 foot ceiling."

Check out the blueprint in the first image and what the finished product would've looked like in the other thumbnail. 

[via Gizmodo]