The 'Washington Invasion' was a series of incidents in the latter part of July 1952, centered on Washington, DC, which came at the peak of a major flying saucer flap that year. Events began in the early hours of July 20 when two radars covering the capital picked up eight UFOs in restricted air space, flying at a few hundred kilometers per hour and suddenly accelerating to a tremendous speed. A number of military and civilian pilots reported seeing strange lights in the sky around the same time.
On the night of July 26–27, more strange lights and radar contacts were logged. Interceptor planes from Wilmington, Delaware were scrambled. One pilot, Lt. William Patterson, reported himself surrounded by a ring of great blue-white lights, which disappeared before he was given permission to fire on them.
In its investigation of the incidents, the Civil Aviation Authority's Technical Development and Evaluation Center concluded that the radar images were the result of temperature inversions which could cause radar signals to be reflected back to the ground. Excitement caused by the radar anomalies could have led to misidentification of ordinary, bright sources of light with mysterious aerial objects.