Bentwaters-Lakenheath, England, August 1956August 1956

Beginning at about 9:30 p.m. on August 13, 1956, and continuing into the predawn hours of August 14, ground-based radar at the U.S. Air Force station at RAF Bentwaters in eastern England detected a series of unidentified radar returns moving at unusual speeds. Over the next six hours, controllers at Bentwaters, at the nearby RAF Lakenheath, and at the RAF area chain control reported a sequence of objects: targets that appeared to merge with one another, that paced or stalled in mid-air, and that reversed direction faster than any known aircraft of the period was capable of doing.

A USAF C-47 transport flying near Bentwaters observed a luminous object pass beneath it. A control tower at Bentwaters and a separate tower at Lakenheath both reported a bright object visible to the eye in the same direction the radar operators were tracking it. By around 11:00 p.m., the activity had shifted toward Lakenheath, and the radar there began tracking new targets that appeared to hover, then accelerate to over six hundred miles per hour without an apparent acceleration phase.

A Royal Air Force de Havilland Venom interceptor was scrambled from RAF Waterbeach to investigate the Lakenheath returns. The pilot acquired the object on his airborne radar, then reported that he could not establish a stable visual track. According to the Lakenheath ground crew's contemporaneous transcript, the object appeared to move behind the Venom and then maintain a position behind the aircraft despite the pilot's attempts to evade by changing speed and altitude. A second Venom was scrambled but did not establish radar contact before the objects departed the airspace.

The Bentwaters-Lakenheath case became one of the most-studied radar-visual incidents of the Project Blue Book era. The University of Colorado's federally-funded UFO study, known as the Condon Committee, examined the case in detail in its 1968 final report. The Committee concluded that the incident could not be attributed to known atmospheric phenomena, equipment malfunction, or conventional aircraft, and singled it out as a case that deserved more thorough investigation than the available records had allowed.

Project Blue Book filed the incident as "unknown," with the case file documenting the radar transcripts from Bentwaters and Lakenheath, the witness statements from the C-47 crew and ground-tower observers, the operational record of the Venom interceptor flights, and correspondence between the U.S. Air Force, the Royal Air Force, and the British Air Ministry about how to characterize the event publicly.

The full case file (44 scanned pages of operational radar logs, air-traffic-control transcripts, witness statements, and inter-agency correspondence between the U.S. and U.K. air forces) is reproduced below as held by the National Archives.