There is no doubt that the rise of the black/phantom helicopter phenomenon began in earnest in the early-to-mid years of the 1970s – and they weren’t just seen in the United States. The familiar, beating sounds of helicopters were also heard above the homes of people in the U.K. Although those helicopter-based incidents began to be reported in the U.K. around September 1973, it wasn’t until shortly after a new year began – 1974 – that word got out regarding what was afoot. It was thanks to the media that the story reached the public domain.

An insider source in the British Government quietly informed the press that an arm of the British Police Force – called Special Branch – was secretly investigating reports of unidentified helicopters, and all across the U.K. Initial fears were that the helicopters were flown by terrorists who were getting ready to launch attacks across the country. No wonder, then, that Special Branch quickly got involved. It quickly turned out, though, that there was no data at all to support the idea that terrorists were the culprits. So, who was responsible? When the story hit the nation’s media, Special Branch released a statement which confirmed their officers were deeply involved in an investigation of the mysterious helicopters, but, admittedly, had very few answers.

One of the areas which was hit by the helicopter invasions was the English county of Cheshire. In response to this onslaught of sightings, the Cheshire Police Force released the following statement: “We don’t know of any reason why the helicopter should make these trips at night. Obviously we are anxious to find out. Apart from anything else, the helicopter crosses one of the main flight paths to Manchester Airport. There is an obvious danger to the aircraft going into the airport. We are very interested to know what is happening. We hope to be able to trace the pilot and put some suggestions to him. It would appear the pilot is in breach of civil aviation laws. A special license is needed to fly a helicopter at night.”

Within days, the Derbyshire Police Force circulated its own statement to the press and the BBC: “All sorts of things spring to mind but we have pretty much ruled out that it is anything to do with illegal immigrants, and nothing appears to have been stolen in the areas where the aircraft has been sighted.”

At the time, not much more was known about the strange helicopters. Today, however, it’s a very different situation. In the 2000s, and as a result of the provisions of the U.K.’s Freedom of Information Act, Special Branch finally released its dossier on the mysterious helicopters. One of the most intriguing files in the large collection of material was titled Alleged Unauthorized Helicopter Flights in Derbyshire and Cheshire.

A Special Branch officer whose name is deleted from the now-declassified files wrote: “The machine was observed on a number of occasions over a period of two weeks to be apparently practicing landings in the vicinity of the sites of quarries and explosive stores in the Derbyshire countryside. Special Branch Constable [Deleted] has made numerous inquiries to discover the ownership and reasons for the flights from various sources but has yet to establish any positive facts. He has contacted an experienced Royal Air Force helicopter pilot with night flying experience who explained that night flying in the Derbyshire areas would be extremely dangerous due to the nature of the terrain and to the number of overhead pylons in the area.”

Roughly eight weeks after Special Branch began to dig further into the Derbyshire-based encounters, a clandestine meeting was held in the heart of London, which was attended by representatives of Special Branch, MI5 – which is the U.K.’s equivalent of the United States’ FBI – and the Ministry of Defense. Further into 1974, ambitious plans were made to have military fighter-planes pursue the helicopters and force their pilots to land their craft. Rather notably, in the immediate aftermath of this decision, the wave of helicopter encounters in the U.K. came to a sudden end. Hmmmm…