GRANITE CITY, ILLINOISFebruary 1952

On the night of February 13, 1952, radar operators at Granite City Engineer Depot in Granite City, Illinois tracked an unidentified object while conducting a bombing run evaluation for the 97th Bombardment Wing. The radar crew was monitoring an aircraft at 29,000 feet when they locked onto a separate target about 40 miles away. At first, the target behaved like a normal aircraft, but when the radar equipment was switched to an expanded scale for closer tracking, the object's behavior became extraordinary.

About 20 miles from the radar site, the object suddenly increased its speed and changed direction to approximately 197 degrees. It then began descending rapidly. During the 25-second window when operators tracked it on the expanded scale, the object's horizontal ground speed registered speeds of 920, 893, 840, 804, and 841 miles per hour. Operators estimated that at one point, the object was traveling at approximately 1,020 miles per hour. The radar tracked the object maintaining a heading around 197 degrees before gradually turning west to about 200 degrees. After losing the close-range plot, radar reestablished contact with the object at about 30,000 feet, heading east.

The Radar Bomb Scoring Group reported that immediate checks of the radar equipment showed it was operating normally, so the unusual readings could not be blamed on equipment malfunction. In their official assessment, the operators concluded the target was most likely another aircraft conducting a practice bombing run, banking and descending across St. Louis before pulling out of its descent and changing course. However, the Air Force's evaluation of the case remained unidentified, and they noted that additional information about atmospheric conditions, particularly temperature inversions at high altitude, would have been helpful in determining whether such conditions might have affected the radar signals.

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