An unidentified flying object (usually abbreviated to UFO or U.F.O.) is any unusual apparent object in the sky whose cause cannot be identified by the observer; though (in a narrower definition) used by investigators and in popular usage, it more loosely refers to alien spacecraft, being one explanation (among several; see extraterrestrial hypothesis) offered for such sightings. Though UFO sightings have occurred throughout recorded history, modern interest in them dates from World War II (see foo fighter), and was further fueled by the Roswell UFO Incident and Kenneth Arnold's coining of the term flying saucer (both of which immediately followed the war); since when governments have investigated UFO reports, often from a military perspective- and UFO researchers have investigated, written about, and created organizations devoted to the subject.
One such investigation, The UK's Project Condign report, notes that Russian, Former Soviet Republics, and Chinese authorities have made a co-ordinated effort to understand the UFO topic and that State military organizations, particularly in Russia, have done "considerably more work (than is evident from open sources)" on military applications which have stemmed from their UFO research. The report also noted that "several aircraft have been destroyed and at least four pilots have been killed 'chasing UFOs'. - Wiki
