U-2s (and other military spy planes) do not have the flight characteristics of many UFOs.
The bona fide UFOs make sharp turns in mid-air (sometimes ninety to one hundred and eight degrees), sometimes split into two or more objects, and change colors as they move.
Other bona fide UFOs hover at very low altitudes (sometimes hundreds of feet).
This thread needs a little more info, so...
Look—many folks serious about this topic find it unlikely that alien visitors are from distant galaxies.
The most disturbing (and more likely) ideas are that they have long-standing underground civilizations (and view us as the “surface savages”), are from another dimension which we don’t understand and can’t measure (like ants can’t understand human cities), or are time travelers from the distant past or future.
It is human arrogance to believe that we are at the top of the pecking order of the universe and have discovered all of the important secrets. I don’t buy it.
I saw one of those 90 degree turn UFOs in the winter of 1967 or 1968 in Andover MA not far from the high activity area of Southern NH where that couple was allegedly abducted not long before then IIRC.
A 90 degree turn is outside physics as we understand it, and certainly there would be no humans on board expected to survive such a turn! I guess these things could just be autonomous robot drones running on cosmic GPS mapping!