So, take this for what it's worth. I have known a few individuals who have been involved in various areas of the military. One was an aircraft engineer working on black projects. One was in COMSEC. One was a nuclear engineer.
One of them walked into the wrong hanger once and was face-to-face with a disc type something-or-other that he was not supposed to see, and was basically told "You didn't see that, and don't ever say you did."
One told of several incidents, and one in particular that was rather startling, tracking objects across North America that were going at seemingly impossible speeds and changing vectors in ways that would tear any convention craft apart. They were picked up on multiple instrument arrays across the country.
One was working on advanced propulsion, real science fiction type stuff, but was moved to other projects when he started asking the wrong questions. I'm being deliberately obtuse here.
There are reliable individuals. They aren't crazy, and they aren't conspiracy nuts.
I am convinced that these things are not anomalies, and that they are terrestrial in origin. All but one of my afore-mentioned friends disagree with me. They think they are alien, but this is only their opinion. None of them had any "inside" knowledge that the military is aware of alien craft. But when you are an engineer, and know what's physically possible given our current level of technology and materials science, I suppose I cannot fault them for jumping to that conclusion.
The thing is, calling it "alien" doesn't solve that particular difficulty. If you assume that the things are real, then what they are doing is physically possible. And if it is physically possible, then it is theoretically possible for us to do it. So applying occam's razor, you don't need to invoke aliens. It is far more likely that someone figured it out, especially someones with multi-billion dollar black budgets working over decades with the brightest minds on the planet.