Hey Sugden,
I was about to write the same post but you beat me to it! I don't live near prestwick or scotland at all for that matter but I have had growing interest of the news on the matter. I believe the Isreali air force have operated through prestwick for many years now but these other US flights are susspect.
Check out this site
http://flightaware.com/live/ and type in the Airport code EGPK (prestwick). This clearly shows both Evergreen International and Atlas air flying From USAF bases to Prestwick. Just seen some of these exact flight details on Chanel 4 news!
Can't seem to find details of where these aircraft are heading to next, but the informations probably out there somewhere.
Hope this helps.
HM!!