You can call this pure conjecture if you will, but here's the story. Several years ago, I knew some people in a PhD physics program, and one of the guys there tells a story about an engineer he worked with during one of his summer internships during undergrad. He described this guy as one of those older rugged not quite polished types. The type that cursed a lot, and didn't really put up with anyone's crap. He was wicked smart though, and he'd been doing it a long time too. The story goes that the one of the government agencies approached him to help them work whatever they were doing at the time. I think he said this was around the 1950s. The engineer asked why should he work with the government when he gets to work on cutting edge stuff all the time anyway. Apparently, they let him see some of the things they had developed to entice him, and he said that it was easily 5 years beyond what anyone had seen.

Is it true? Honestly, I don't know, but the guy telling the story at the time believed him, and this was in the same conversation where scientists were talking about how they could use satellite imaging to track where someone had walked 10 minutes before in a field. That was the unclassified version of what they could talk about.