Skunkworks projects (U-2 and SR71) IIRC.
I was stationed at a place (Kadena) where the SR flew almost daily, headed west. We called them the “Habu” at the base, locally. There were also one or two U-2s around.
There’s the old tale of how Kennedy was going to announce the new 3000 MPH plane, the RS71. He said “SR71” and they ended up changing the designation.
What’s next? Well I don’t believe it’s a hypersonic vehicle to move stuff or people from one place to another. I could believe a kill vehicle with something like a daisy cutter / bunkerbuster , or even an EMP on board for a one-way trip.