On the nights of July 19–20 and July 26–27, 1952, radar operators at Washington National Airport and Andrews Air Force Base simultaneously tracked unidentified objects over the restricted airspace above the U.S. capital; intercepting F-94 jets found the objects only to watch them vanish from radar, then reappear when the fighters departed.

Senior controller Harry Barnes stated the objects' 'movements were completely radical compared to those of ordinary aircraft.' The incident prompted the largest USAF press conference since World War II and alarmed the Truman administration enough to produce the Robertson Panel in January 1953. Project Blue Book attributed the radar returns to temperature inversions.