Houm, AlabamaNovember 1957

On November 21, 1957, radar operators at Houm, Alabama, picked up an unusual target on their screens. The object appeared to be 15 miles long and 10 miles wide, moving slowly at about 55 knots (roughly 63 miles per hour). The radar signal was light yellow with bright spots within it. Three experienced Air Force radar specialists tracked the target as it moved toward their station, watching it slowly descend from an initial altitude of about 36,700 feet to roughly 3,000 feet before it faded away.

The operators considered several explanations as they watched the target. They ruled out weather, which seemed unlikely to move so fast while maintaining such a large size. They also considered chaff (radar-reflecting strips dropped from aircraft), but the target's enormous dimensions made that seem improbable. Significantly, civilian airliners passing 35 miles north of the track were asked to search for the object on their own radar equipment, but found nothing.

Three hours after the radar blip disappeared, the operators discovered a serious problem: the height-measuring equipment had not been functioning correctly. The error was substantial enough to affect the altitude readings by tens of thousands of feet. This equipment failure undermined confidence in the radar data. Air Force officials reviewing the case concluded that without any actual visual sighting of an object so large, and given the inability of airborne radars to detect anything in the area, the radar return must have been false, likely caused by some weather-related phenomenon or radar reflection.

The full case file, consisting of 7 pages, is reproduced below as held by the National Archives.