The MiG-21F is a short-range day fighter-interceptor and the first major production version of the MiG-21 series, one of many versions that served in the arsenals of nations around the world. The E-5 prototype first flew in 1955 and made its first public appearance at the Soviet Aviation Day display at Moscow's Tushino Airport in June 1956. During the Vietnam War, MiG-21s were often used against U.S. aircraft, and between April 26, 1965 and January 8, 1973, USAF F-4s and B-52s downed 68 MiG-21s. More than 30 countries, including nations friendly to the U.S., have flown the MiG-21, and at least 15 versions were built, with more than 8,000 produced, exceeding the production total of any other modern jet aircraft. The MiG-21F in question has an unknown history, but it is known to have been built as one of thousands for foreign export and is painted and marked as a North Vietnamese Air Force MiG-21F as flown during the Vietnam War. Two 8th Air Force B-52D tail gunners are credited with downing two MiG-21Fs, one each.