Even the few Secrets that I was made privy to would amaze people.
I had a project where the client wanted to look behind a tunnel wall and determine the locations of wooden pillars inside of the tunnel 10 feet or more behind the wall.
Ground penetrating radar would probably work if the pillars are adjacent to the wall, but not 10 feet away. So I called a guy that was (RIP) an expert in this type of thing.
“Yeah - that’s a tough one. Nothing on the market will do it I don’t think. The government could do it easily enough.”
He did R&D with the government on certain things so I just took him at his word and didn’t press the subject.