If you do a search for it, you'll find many entries. And I have a personal story to tell you about something I witnessed with a friend in the early 1990s, when "black unmarked helicopters" flew all over our local skies, including my house often, and seen by visitors.
They weren't a conspiracy theory. They were there.
Anyway, my friend and I would take off in my truck if it was winter and hers in the summer (she had AC) and go tramping in the woods exploring.
One day we were headed north to Alabama on a main artery and I looked in the side mirror and was horrified at the size of the black helicopter just above and in back of us. I asked her to look -
it was above us now. There it was - a huge, black military helicopter, unmarked, and MAKING NO SOUND AT ALL. In complete silence, it veered over us to the right and we could see it fly over a sod farm. It was low and silent. We had slowed down to watch it go. Couldn't believe what we had seen.
And as we watched it, it just d i s a p p e a r e d...
We get together often, and we talk about "that day with the helicopter"...which we will NEVER forget.