Monmouth, New JerseySeptember 1951

On September 10-11, 1951, the U.S. Air Force received reports of unidentified objects near Fort Monmouth, New Jersey. The sightings involved both visual observation by aircraft pilots and radar contact at the fort. Here is what the Air Force investigation found.

On September 10, two Air Force pilots flying a T-33 aircraft spotted an unidentified object over Sandy Hook, New Jersey. The pilots watched the object for approximately two minutes as it traveled at high speed. The object appeared silver in color, round or disc-shaped, and moved without any visible means of propulsion. The pilots estimated it was roughly the size of an F-86 fighter aircraft.

The same day, radar operators at Fort Monmouth detected multiple targets on their screens. One target moved at an extremely fast speed and presented radar returns too strong to be explained by equipment malfunction. The operators initially thought they had spotted a ship before recognizing the object's extreme speed made that impossible.

On September 11, additional radar sightings were reported at Fort Monmouth. Operators tracked targets moving at speeds exceeding the radar sets' maximum aided tracking capability of 700 miles per hour (1,130 kilometers per hour). The radar operators described one target as remaining nearly stationary before rising almost vertically at an extremely rapid rate.

The Air Force's investigation concluded that the September 10 visual sighting by the pilots was probably a weather balloon launched from Evans Signal Laboratory a few minutes before the aircraft arrived in the area. Two of the radar sightings were attributed to weather balloons. The remaining radar returns were likely caused by anomalous propagation (unusual atmospheric conditions that create false radar echoes) or were influenced by the operators' expectations after hearing about the pilots' sighting. One radar return from September 11 could not be explained and remains unknown, though anomalous propagation was considered the probable cause.

The file notes that the radar operators were students undergoing training rather than experienced personnel. Some of the unusual readings may have resulted from operator inexperience or excitement caused by earlier reports of the sighting. The investigation revealed that news of the pilots' report had spread quickly, and Fort Monmouth personnel had been alerted to watch for unusual targets, which may have influenced their interpretations of what they observed on the radar scopes.

The complete case file, containing 87 pages of documents, is reproduced below as held by the National Archives.