The 1974 Project
It's no secret that every military branch keeps secrets from the general public. The Air Force easily has some of the best-kept secrets out there, which is why the public is so interested in what they're up to! One project of the Air Force that thinned the veil was the 1974 Project. The plans for this project were eventually released and declassified after it never went through. This was a plan for a supersonic flying saucer, but it's not clear why they were trying to build it...