#36: Top Secret Secrets
The speculation that the US government conducts top-secret experiments is as classic as the widespread stories about alien abductions. At this point, learning about a government cover-up of high-tech planes and alien encounters is a canon event. While we may never know the cold hard facts about any possible secrets, it does seem likely that they exist.
Why wouldn’t they exist? Every government in the world does stuff that its regular citizens have no clue about. The US has a sizable military budget, and a lot of that is probably spent on research and development. Hiding certain technological advancements just seems smart at this point. Understandably, they wouldn’t want other countries stealing their ideas or making weapons with their own technology to use against them.