JD - I think I saw a pic of one in AFM a year or two ago, passing through Mildenhall. Yes, i know it's basically a B57 airframe on steroids but with the wing mounted engines it could look from a distance like a Dragon with the wing pods. Check the NASA website
http://www.nasa.gov/images/content/49586main_wb_2.jpg. Actually, the more I look at it, especially the wing shape, the less I'm sure. Oh, bu$$er, ignore everything after good evening then.
Possibly a U2 going up for a sniff at Machrihanish? Mahoosive track, no one for miles and some SEALs (in those days) to keep an eye on it should it have to stay? Can't think of a better place to have an out of the way div for such a beast. The place is now owned by HIAL and the killers have long since gone so I don't think they'll be one there any time soon. I'm sure I was told that they also shot approaches at Lossie/Kinloss too??