1952 Washington, D.C., UFO incident
From July 12 to 29, 1952, a series of unidentified flying object (UFO) sightings were reported in Washington, D.C., and later became known as the Washington flap, the Washington National Airport Sightings, or the Invasion of Washington. The most publicized sightings took place on consecutive weekends, July 18–19 and July 26–27.
Source: Wikipedia — 1952 Washington, D.C., UFO incident (CC BY-SA 4.0)