No doubt some portion of all UFO reports are due to secret military aircraft. However, the most interesting, and convincing reports are not likely to be explainable in this way. They feature motions that seem to virtually ignore the laws of physics, such as extreme acceleration and 90 degree turns. We would have to grant to some unknown sector of the military a technology so far beyond what is generally known as to seem even less probable than the possibility of extraterrestrial visitors. Further, it would have to extend back many decade in time to account for what has been reported, making it an even more remote improbability. We must also account for the fact that such reports often involve objects over major cities. Why would a super-secret branch of the military, intent on concealing a vastly advanced technology allow its aircraft to be seen in such circumstances? Michael