The US government might still be keeping aliens from the world, but they're no longer keeping this schematics of a supersonic flying saucer the US Air Force was considering trying to build back in the 1950s. Meet Project 1794.
According to recently declassified documents, Project 1794 was intended to yield a terrestrial flying saucers that could "[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." In addition, the finished product would have taken off and landed vertically, like any flying saucer should.
Ultimately the project was scrapped in 1960 when prototypes had a little bit of trouble living up to the "100,000 ft ceiling" part, and had a bit of trouble so much as reaching double digits. So now all we're left with is a whole bunch of "what if"s and some government documents with pictures of USAF-branded flying saucers on them. Surely that's worth something, right? [National Archive Blogs via Wired]