The RAF Topcliffe "Perfect Flying Saucer" During Exercise Mainbrace

September 1952. NATO was staging Exercise Mainbrace, a simulated Soviet attack on Western Europe. About 80,000 personnel, more than 200 ships and about 1,000 aircraft took part.

In London, flying saucers were already on official minds. In June 1951 the Flying Saucer Working Party had advised against further investigation "unless and until some material evidence becomes available". On 28 July 1952 Winston Churchill asked: "What does all this stuff about flying saucers amount to? What can it mean? What is the truth?"

Friday, 19 September. Just before 11 am. At RAF Topcliffe, near Thirsk in North Yorkshire, Avro Shackleton crews of 269 Squadron were waiting for orders. A Gloster Meteor was coming in to land at nearby RAF Dishforth.

Flight Lieutenant John Kilburn saw "a white object in the sky", "silver in colour and circular in shape", between ten and twenty thousand feet. It trailed the jet by some five miles, moving slowly on a similar course. Then it began to descend, "swinging in a pendular motion during descent similar to a falling sycamore leaf". The Meteor turned towards Dishforth. The object seemed to follow. It stopped. It began to rotate on its own axis.

"Suddenly it accelerated at an incredible speed towards the west turning onto a south-easterly heading before disappearing," Kilburn wrote. "All this occurred in a matter of fifteen to twenty seconds." He added: "The movements of the object were not identifiable with anything I have seen in the air and the rate of acceleration was unbelievable."

Ten officers and national servicemen from 269 Squadron watched, according to historian David Clarke. The press named Kilburn, Flt Lt Cybulski, Paris and Master Signaller Thompson. The Sunday Dispatch ran "'Saucer' Chased RAF Jet Plane" with a photograph of five of the airmen. Kilburn later called it "a perfect flying saucer". The RAF would not call the report serious. But, it said, "It is being investigated."

Kilburn's statement survives at The National Archives in file AIR 16/1199. The Air Ministry's own study has been lost. Its only trace is a 1967 memo by DI55 desk officer John Dickison, released in 1998. He called the "Topcliffe-Meteor incident" "typical of reports about such aircraft at that time". There was no specific evidence the object tracked the Meteor, he noted, and its path was "not established in absolute terms".

A CIA memo by H. Marshall Chadwell said Dr R.V. Jones was "distressed" at press coverage of the Shackleton crews' sightings. Edward J. Ruppelt later wrote: "It was these sightings, I was told by an RAF exchange intelligence officer in the Pentagon, that caused the RAF to officially recognize the UFO." Clarke dates the Air Ministry's UFO desk to 1952. History.com says 1953.

No one has accused the Topcliffe witnesses of a hoax. Dickison's memo points to a misperception tied to the aircraft. For Mainbrace as a whole, weather balloons, meteors and clouds have been suggested. No published sceptical study of Topcliffe itself has been found. Months later, an Air Ministry official told a newspaper: "We take those stories with a large spoon of salt, old boy."

Topcliffe was one of several Mainbrace reports. On 20 September reporter Wallace Litwin photographed a "white sphere directly overhead" from USS Franklin D. Roosevelt. Only a poor print reached the Blue Book files. Clarke and Andy Roberts covered the era in Out of the Shadows. In March 2020 the History series Project Blue Book closed its second season with a heavily fictionalised "Operation Mainbrace".