For what it’s worth, secret military programs might be called UFO’s. And being that military programs tend to happen around military bases, military people would be the most likely to notice them.
In the 1960s there was a bestselling book on UFOs called Flying Saucers: Serious Business, by Frank Edwards. Edwards actually discusses how the style of UFOs evolved over the years and includes pictures. Incredibly, though, Edwards doesn’t even mention the obvious conclusion – that people were faking the pictures and mimicking what UFOs looked like in movies. Instead, he implies that the aliens were upgrading their designs.
I read this book when I was a kid and thought it was the coolest thing ever … but even back then, I noticed that the UFOs in the oldest pictures were oddly old-timey looking.