FWIW, in a section where Ross Anderson (Security Engineering, Ross Anderson, Third Edition, p. 329.) talks about military combat aircraft and IFF systems, he mentions how militaries hide their submarines’ top speeds and other capabilities, from other nations. So with aircraft, they have to do things to disguise their top speeds.
Then he drops this interesting tidbit:
"And as for air combat, some US radars won’t display the velocity of a US aircraft whose performance is classified, unless the operator has the appropriate clearance. When you read stories about F-16 pilots seeing an insanely fast UFO whose speed on their radar didn’t make any sense, you can put two and two together.
He seems to be saying that radar (possibly unbeknownst to the actual people monitoring the radar!) is doing strange things to disguise aircraft speed. This could explain a good sized fraction of UFO reports by the military--if it's all correct. If you know more about military radar than Ross Anderson, and just exactly how it can disguise aircraft speed, please let us know.