The incident had been known as Britain's Roswell: a group of American servicemen stationed in Suffolk go into a forest to investigate mysterious lights and emerge convinced they have seen an alien spacecraft.
The sightings, in December 1980, remain unexplained and have become the country's most tantalising and enduring UFO riddle.
One of those involved even claimed to have touched an alien spacecraft.
Now, the man who led the only investigation into the “Rendlesham Forest Incident” has spoken about the sightings - but his decision to end thirty years of silence is unlikely to please the UFO-believers as he suggests his men could have been hoaxed.
In 1980, US Air Force Colonel Conrad was base commander of the twin airfields of Woodbridge and Bentwaters, near Ipswich, which are understood at the time to have stored nuclear weapons.
Just after Christmas mysterious lights were seen in the sky above nearby Rendelsham Forest, and after a second night of reports from his men, Col Conrad investigated himself.
During the day, he went into the forest himself to a clearing where the lights had been seen and where markings on trees and on the ground had been found, indicating a possible landing by a spacecraft.
Col Conrad said he found them "unremarkable". Nevertheless, he returned to the base and hand picked a team of his best security officers and sent them in the forest that evening to investigate.
Armed with a Geiger counter, cameras and night vision devices they staked out the "landing site". After seeing nothing suspicious, most of the team returned to base late that night. A handful remained, including his deputy, Lt Col Charles Halt, who stayed in contact with his superior by radio.
It is his account of what happened next which has fuelled rumours of a UFO landing. Over the radio, he reported seeing more lights on the ground and in the sky.
At home on the base, the commander and his wife went outside to look for the lights after hearing about the sighting. Other senior officers on the base – and their wives – did the same. But despite it being a clear, cloudless night, they saw nothing suspicious.
Lt Col Halt filed a report of the incident to the Ministry of Defence some days later and has since go on to say the lights he saw were “extraterrestrial in origin” and accuse the US and UK security services of a cover-up. Col Conrad, who had gone home convinced he had seen nothing unusual, has remained silent.
Now he has provided a series of statements about the sightings to Dr David Clarke, a Sheffield Hallam University academic and the UFO adviser to the National Archives - which this week will release some Ministry of Defence files relating to the incident.
"We saw nothing that resembled Lt Col Halt's descriptions either in the sky or on the ground," Col Conrad said.
In a damning indictment of his former deputy, Col Conrad added: "We had people in position to validate Halt's narrative, but none of them could."
He said there was no "hard evidence" of anything suspicious.
The Geiger counter was initially said to have given slightly elevated readings in the clearance, but that these were later found to indicate "normal" levels of background radiation.
Col Conrad is scathing about his former deputy.
"He should be ashamed and embarrassed by his allegation that his country and England both conspired to deceive their citizens over this issue. He knows better," he said.
The former base commander also disputes the subsequent testimony of another serviceman, Sgt Jim Penniston, who had gone into the woods on the first night of the sightings and has since claimed he touched an alien spacecraft.
Col Conrad said he interviewed the officer at the time and that, while he described seeing strange lights which had moved off into the distance, he had not mentioned touching a spacecraft.
Although he cannot explain the subsequent accounts of his subordinates, Col Conrad said he thinks the incident may have been a hoax.
Col Conrad said: "The search for an explanation could go many places including the perpetration of a clever hoax. Natural phenomenon such as the very clear cold air having a theoretical ability to guide and reflect light across great distances or even the presence of an alien spacecraft.
"If someone had the time, money and technical resources to determine the exact cause of the reported Rendlesham Forest lights, I think it could be done. I also think the odds are way high against there being an ET spacecraft involved, and almost equally high against it being an intrusion of hostile earthly craft."
Dr Clarke, who is a sceptic on UFO issues, believes Lt Col Halt saw some form of optical illusion and that his and Sgt Penniston's claims have become increasingly extreme over the years, as speculation over the sightings has increased.
"I don't think anyone, least of all Conrad, doubts that Halt and his men saw "something" in the woods. They had an extraordinary experience. And that experience would remain extraordinary regardless of whether ultimately it was a lighthouse or poacher's lanterns – which has also been suggested.
"But Col Conrad is responsible for the only proper investigation of this incident. He went to look and if there was anything to be seen, I cannot see how he could not have seen it."