The 1952 Washington, D.C. UFO flap

In July 1952 radar operators and pilots around Washington, D.C. reported unknown lights and blips over the capital. The Air Force answered with a news conference that CNN calls its biggest and longest since World War II.

By the account of the National Investigations Committee on Aerial Phenomena (NICAP), a UFO advocacy group, in The UFO Evidence (1964), the first night began at National Airport around 11:40 p.m. on July 19. Observers on the ground and military and airline pilots reported strange lights, and up to ten unknown blips showed on radar. NICAP says the returns hovered, sped up suddenly and moved very fast until close to dawn, and that objects trailed and overtook arriving airliners.

Edward J. Ruppelt, former head of Project Blue Book, wrote in 1956 that the radar sightings at Washington National Airport and Andrews AFB pushed the Democratic National Convention off the front pages. He said he fielded questions from the President's office and from reporters in London, Ottawa and Mexico City, and that a near riot broke out in the Roger Smith Hotel's lobby when he would say nothing to U.S. reporters. Maj. Gen. John Samford, the Air Force's intelligence director, then called a news conference that CNN describes as the Air Force's biggest and longest since World War II.

In the Condon Report (1968), Gordon D. Thayer found that the radar tracks from Andrews AFB, Bolling AFB and Washington National Airport mostly failed to match each other, airborne sightings or ground reports, beyond loose links such as a star seen in the direction a radar track gave. Wikipedia notes that Michael Wertheimer, who looked at the case for the Condon study in 1966, said those who had watched the radar still disagreed with the Air Force.