Details about the case can be read in the main page devoted to Operation Mainbrace.
Whilst investigating several local cases recently, Hull based ufologists, Gary Anthony and Chris Evers, stumbled across this interesting article, from a 1952 newspaper. The headline screamed at them from the page, "'FLYING SAUCER' JOINS IN 'MAINBRACE'".
A scan of the newspaper page is provided at the bottom of this page.
The article is here reprinted for your information.
A Flying saucer entered exercise Mainbrace today following a report from the RAF station at Topcliffe (York's), of a white object having been seen, which accelerated at a speed in excess of a shooting star.
RAF officers at the Mainbrace headquarters at Pitreavie (Fifeshire) would not state what view was being taken of the report.
A RAF spokesman refused to comment himself whether the report was regarded as a serious one. He added "It is being investigated."
The report led to a NAAFI saucer being placed on the plot of the exercise. The saucer, fastened with ribbons, was placed on the plot alongside the name Topcliffe, and the RAF duty controller at Pitreavie open up a new signal file, headed "SAUCER SIGHTINGS AND MOVEMENTS," where he could file further sightings of the object.
The object was seen by about 10 RAF officers and men, the crews of Shackleton aircraft operating from Topcliffe. The signal reporting what they had seen was passed by the intelligence officer at Topcliffe to the maritime headquarters at Pitreavie and to coastal command headquarters at Northwood, Middlesex. The signal said that the object was seen at 10:53 am yesterday, when a Meteor aircraft was flying at 5000 ft and was descending. A white object was seen five miles astern of the aircraft at approximately 15,900 ft.
It was moving at a comparatively slow speed on a course similar to that of the aircraft. The object was silver in colour and circular. It maintained a slow forward speed before beginning to descend, swinging like a pendulum.
It was thought by those who saw it to be a parachute or cowling from a meteor, but an RAF spokesman said today that no cowling or parachute had fallen in the vicinity of the station.
The signal reported that the aircraft turned towards Dishforth and the object, while still descending appeared to follow.
It then began a rotary motion about its own axis, but it suddenly accelerated at incredible speed in a westerly direction, then turned to a south-easterly course.
Those who saw it stated that its movements were not identifiable with anything they had seen in the air and that the acceleration was in excess of that of a shooting star.
The duration of the incident was between 15 and 20 seconds. The object was seen by Flt.-Lt. Kilburn and Flt.-Lt. Cybulski, both captains of aircraft, by FO Paris, Master Signaller Thompson, and by about 6 other aircrew members.