Without warning, the orange UFO swooped toward them.
The crew of the RAF Vulcan bomber banked hard and radioed they were being chased across the Atlantic by a large mysterious object.
The incident was classified as a UFO sighting and the details were immediately locked away.
Now, 30 years later, the extraordinary encounter is among thousands of previously secret cases contained in the government's "X-Files" that officials are to release in their entirety.
The cases, many from a little-known defense intelligence branch tasked with investigating UFO claims, will be published by the Ministry of Defense (MoD) to counter what officials say is "the maze of rumor and frequently ill-informed speculation" surrounding Whitehall and its alleged involvement with Unidentified Flying Objects (UFO).
The public opening of the MoD archive will expose the once highly classified work of the intelligence branch DI55, whose mission was to investigate UFO reports and whose existence was denied by the government until recently. Reports into about 7,000 UFO sightings investigated by defense officials - every single claim lodged over the past 30 years - are included in the files, whose staged release will begin in spring.
The decision to release Whitehall's full back-catalogue of UFO investigations was taken last month after the Directorate of Air Space Policy, the government agency responsible for filtering sensitive reports, gave its permission to publish the biggest single release of documents in MoD history. Now the government fears a repeat of the unprecedented demand and the website crash experienced by the French national space agency in March when it released its own UFO files. Government IT experts are believed to have drawn up contingency plans to avoid a repeat scenario when Britain's dossiers are finally made public.
Among the first tranche of UK cases will be the official government files into the famous Rendlesham incident, in which a UFO that apparently landed in Rendlesham Forest, Suffolk turned out to be a hoax.
Another case chronicles a series of reports sent to RAF Scampton, Lincolnshire, by the crew of a Vulcan bomber on exercise over the Bay of Biscay early on May 26, 1977. According to documents to be released, five crewmen, including the captain, co-pilot and navigators, watched "an object" approach their aircraft at 14,000 m above the Atlantic.
An intelligence report sent to the MoD says the crew "were unable to offer a logical explanation for the sighting".