OPERATION MAINBRACE

Opening

In September 1952 NATO ran Exercise Mainbrace, the first large exercise of its new Allied Command Atlantic: around 200 ships, about 1,000 aircraft and some 80,000 personnel, defending the northern flank off Denmark and Norway. During those two weeks, crews and airmen from three countries reported unidentified objects: a Danish destroyer off Bornholm, RAF officers at Topcliffe in Yorkshire, and men on the deck of the American carrier USS Franklin D. Roosevelt, where a reporter photographed a round white object overhead.

Edward Ruppelt, then running Project Blue Book, wrote that nobody had expected UFOs to turn up for the exercise. The photographs went to the Navy and the Air Force, a poor print ended up in the Blue Book files with no analysis attached, and the case has never been explained.

Timeline

13 or 14 September 1952Exercise Mainbrace begins. Sources give the dates as 13 to 23 or 14 to 25 September.

13 September 1952North of the Danish island of Bornholm, Lieutenant Commander Schmidt Jensen and the crew of the destroyer Willemoes report a triangular object with a bluish glow moving fast to the southeast. Jensen's speed estimate is usually given as about 900 mph, though some sources say 1,500.

19 September 1952, about 10:53At RAF Topcliffe in Yorkshire, a silvery disc is seen following a Gloster Meteor as it returns to the base. Flight Lieutenant John Kilburn of 269 Squadron and other aircrew on the ground watch it descend with a swinging, pendulum-like motion. When the Meteor turns, the object stops and rotates, then moves off to the west at high speed before turning southeast and disappearing.

20 September 1952, about 4 p.mOn the flight deck of the USS Franklin D. Roosevelt, a commotion among crew and pilots draws the attention of Wallace Litwin, a civilian reporter aboard, to a round object high overhead. He takes a series of colour photographs. A ship's officer reportedly confirms that no weather balloon had been launched in the area. Some sources give the date as 19 September, but the Navy records cited by NICAP give the 20th.

20 and 21 September 1952The Topcliffe sighting runs in the Yorkshire Evening Press and the Sunday Dispatch.

October 1952Copies of Litwin's pictures reach Air Force intelligence, forwarded as three Ansco transparencies.

1956Ruppelt's book describes the Mainbrace sightings, and repeats what an RAF exchange intelligence officer in the Pentagon told him: that these sightings were what caused the RAF to officially recognise the UFO.

Key figures

Admiral Sir Patrick Brind commanded the exercise. Lieutenant Commander Schmidt Jensen reported the Willemoes sighting. Flight Lieutenant John Kilburn wrote the Topcliffe statement now held in the UK National Archives. Wallace Litwin, a reporter aboard the Franklin D. Roosevelt, took the photographs. Edward Ruppelt recorded the case for Project Blue Book, which had already been through the Washington sightings that summer.

Physical and documentary trail

Kilburn's Topcliffe statement survives in the UK National Archives. The Blue Book files hold a poor print of one of Litwin's photographs, with no analysis report attached. The Navy examined the photographs, and the Air Force received copies in October 1952. The originals were not made public for decades. Images attributed to Litwin now circulate online, but their chain from the 1952 transparencies is not documented.

Litwin's own later accounts do not fully agree. A letter written decades afterwards differs from his 1974 correspondence on the balloon question and the number of photographs, and adds a claim that the carrier was secretly carrying an atomic bomb, which the Navy denied. How well his later memory held is unknown. The Danish and wider NATO records of the exercise sightings are not among the published sources.

The movements of the object were not identifiable with anything I have seen in the air.

Things you might not know

• It was a very big exercise. Parliament was told in October 1952 that some 220 ships took part. Units from eight NATO governments and New Zealand were involved.
• Its purpose was reassurance. Mainbrace was meant to show Denmark and Norway that NATO could defend them from a Soviet attack.
• The Topcliffe disc fell like a leaf. Kilburn compared its swinging descent to a falling sycamore leaf.
• The RAF story is second-hand. Ruppelt's line that Mainbrace made the RAF officially recognise the UFO came from what one RAF officer told him, not from a published RAF document.
• The photographs stayed out of sight. The Air Force had copies by October 1952, but the pictures were not made public for decades.
• It made it to television. The season 2 finale of the History series Project Blue Book, in 2020, was built around Mainbrace.

Competing explanations

Balloons. A weather or research balloon at height can look like a white sphere against a blue sky, and Litwin himself first took the object for one. The ship's officer's report that no balloon had been launched in the area weakens this for the carrier sighting, though a balloon from elsewhere cannot be ruled out. It fits the Topcliffe manoeuvres less well.

Aircraft, reflections and misjudged distance. With about 1,000 aircraft in the exercise, the skies were crowded. A distant aircraft catching the sun could account for some reports. It is a poorer fit for an object that stopped, rotated and then sped away while a Meteor circled.

Something the exercise could not identify. The witnesses were naval crews and RAF aircrew, the reports came from three separate places over a week, and Blue Book never explained the photographs. On this reading the case stays open because the evidence that would test it, the original transparencies and the Navy's analysis, has never been published.

Later life of the case

Mainbrace is now usually told as the moment the British military began to take the subject seriously, largely on the strength of Ruppelt's second-hand line. UK National Archives releases have made the Topcliffe statement public. The Navy's analysis of Litwin's photographs has not been released.

Finding

During a major NATO exercise in September 1952, trained observers in three places reported objects they could not identify, and one of them was photographed in colour from the deck of an American carrier. The reports are documented, the witnesses were military, and Blue Book never explained them. A balloon is the strongest ordinary explanation for the carrier photographs, but the record does not show one, and it does not fit the Topcliffe account well.

What still will not resolve: Litwin's original transparencies and the Navy's analysis of them, which would show what was over the Franklin D. Roosevelt on 20 September 1952.