Project Paperclip - An actual true conspiracy
This isn't really that sinister a conspiracy but it was a top-secret project for years before knowledge of it basically became harmless history. This is a neat thing to know about. Educate yourself on the relationship between our government and Nazi Scientists!

"The U.S. Military rounded up Nazi scientists and brought them to America. It had originally intended merely to debrief them and send them back to Germany. But when it realized the extent of the scientists knowledge and expertise, the War Department decided it would be a waste to send the scientists home. Following the discovery of flying discs (foo fighters), particle/laser beam weaponry in German military bases, the War Department decided that NASA and the CIA must control this technology, and the Nazi engineers that had worked on this technology. "

http://www.mt.net/~watcher/nwonazi.html