There’s no knowing exactly what was seen by the American servicemen at RAF Alconbury, but those who witnessed the strange being said it moved with an unnatural speed, hurdling two fences in one giant leap.
The men who saw it open fired. But it made no difference, it disappeared without a trace into nearby woods.
The story of the encounter, which is said to have taken place in 1973/4, is one collected by a retired policeman and his partner who have compiled a series of books on unexplained phenomena.
And there are more that feature in Huntingdonshire - unexplained children's voices, a claim that the Earl of Sandwich had a close encounter with a werewolf at Hinchingbrooke House, and an object which disturbed a teenager tending to her horse in Godmanchester.
John Hanson, who was an officer in the West Midlands for 30 years - 15 of them with CID - began to catalogue sightings in 1995. Haunted Skies, written with partner Dawn Holloway, is now reaching its 10th volume, covering the years 1987-88.
Mr Hanson, who lives near Redditch, said: "If anyone had told me years ago that I would be doing this I would not have believed them. If anyone had told me that they had just seen a flying saucer I would have thought they were bonkers or had too much to drink."
His interest was sparked as he was retiring. His son, now a detective chief inspector, told him of an incident he had witnessed and this changed his views forever.
"My son was called to an incident in which a doctor told them there was something strange in a copse close by. He and a policewoman went to investigate and saw an object which as they approached seemed to shrink into itself and disappear," he said.
The object, the length of a double-decker bus, looked like two inverted plates, one on top of each other, surrounded by a blue field of energy hovering in the air. Running through the middle was a horizontal band of orange light, and over its surface was what looked like thin supporting ribs.
"This triggered my curiosity to find out whether there is any truth or reality in all this, or whether it was all in the mind. I have since spoken to many people, including senior pilots and servicemen, all over the world who have seen many things that they just can't explain. I don't know, and they say themselves, they don't claim to know, the origin or whether they are extra-terrestrial - it's just inexplicable phenomenon.
"All they know is that they are unexplained, which set me on my quest to record as many sightings or experiences as possible. They are part of our social history and should be preserved."
Sightings are reported to Mr Hanson by people who have heard of Haunted Skies and want their experiences recorded. In Huntingdonshire that included the reports of a 'creature' that broke into RAF Alconbury.
Marc Uptergrove, of Los Angeles, said that his father received a radio call one evening stating there was an intruder within the perimeter fence and shots had been fired. He raced out in his truck and sped towards the location of the shooting. Seeing a figure in the fog, he pulled over, thinking it was one of his guards. He rolled down his window and was screamed at by a man-like, bipedal creature. He said the thing ran off at incredible speed and his father drove after it. Within moments it had sped past another of the guards, who also fired, before it fled from the area.
The creature, he said, was hairy, and had intelligent, human-like eyes, a flat nose, and large ears. The teeth were large but not fanged and the lower face was rounded.
That was not the only strange event at Alconbury. Mr Hanson had further contact from airmen who were disturbed by the sound of children's voices.
"When we did our research we discovered that there were a number of children that were amongst those killed nearby when a stationary train was hit by The Flying Scotsman in 1897," Mr Hanson said.
Then there was a sighting by Pauline Emerson, who in March, 1988, lived in Bridge Place, Godmanchester. Then aged 14, she was feeding her horse when something frightened the animal.
She said she heard a faint noise, which she took to be an aircraft, glanced upwards and saw a black dense square with a 'bump' in its middle, covered in perforations with what looked like antennas sticking out of each corner. About one and a half metres wide and 20 metres long, as it passed overhead, it made a disgusting noise, leaving a horrible smell in the air. She ran into the house screaming for her mother and father.
During an interview Pauline, who now lives in Lincoln, said that her eyesight had been affected by the incident - she complained of blurred vision and was later treated for enlarged pupils.
At Hinchingbrooke House, Mr Hanson said, the Earl of Sandwich was alleged to have demolished a wing of the building because he claimed it was inhabited by a werewolf.
There is no let-up in Mr Hanson's quest - as soon as volume 10 is finished, work will begin on volume 11 - this time focussing on the Essex area.
INFORMATION: Contact Mr Hanson via email@example.com.