The F-4 was used extensively during the Vietnam War. It served as the principal air superiority fighter for the U.S. Air Force, Navy, and Marine Corps and became important in the ground-attack and aerial reconnaissance roles late in the war. During the Vietnam War, one U.S. Air Force pilot, two weapon systems officers (WSOs), one U.S. Navy pilot and one radar intercept officer (RIO) became aces by achieving five aerial kills against enemy fighter aircraft. (sources wikipedia)