On December 9th 1965 hundreds of witnesses in Michigan, Ohio, and Pennsylvania observed a UFO crash. The US Military showed up at the scene, confiscated the UFO, and has not been seen since.
UPDATE!! In recent news Oct 26th 2007: NASA to search files on '65 UFO incident. Government agency fought the move in Federal court Full article here: http://www.msnbc.msn.com/id/21494221/