Less than two weeks before the more famous Roswell incident of July 1947, when it is alleged that a flying saucer crashed in the New Mexico desert, Kenneth Arnold saw nine “UFOs” flying at high speed.
Mr Arnold, 32 at the time, said he was flying from Chehalis to Yakima, both in Washington, at the time and was startled by a strange flash of light.
He said: “I observed a chain of nine peculiar looking aircraft flying from north to south” near Mt Rainier”.
The private pilot said he was at about 9,200 feet, and it was about 3pm as he watched the craft for up to three minutes.
He estimated they travelled at a minimum of 1,200 miles an hour.
He landed at Yakima, and after telling a friend who did not believe him, details of his encounter got out.
Initially he described them as “pie pans”, almost like a crescent or boomerang, but added that they were like “saucers skipping on water”.
The media coined the term flying saucers after that.
US Army Air Force officials Lt Frank Brown and Capt William Davidson of Hamilton Field in California, interviewed Mr Arnold on July 12.
He also wrote a report on the encounter.
The military men concluded in a report he was telling the truth, but had seen a mirage.
The report said: “It is the present opinion of the interviewer that Mr Arnold actually saw what he stated he saw.
“It is difficult to believe that a man of his character and apparent integrity would state that he saw objects and write up a report to the extent that he did if he did not see them.”
A number of explanations were given including that he saw snow-capped peaks of the Cascade Mountain Range, meteors, spots of water on the window, orographic clouds, which rise up, or even pelicans.
In an interview three years later, Mr Arnold claimed to have had three further similar sightings, as had other pilots.
He said: “Being a natural-born American, if it’s not made by our science or our army air forces, I am inclined to believe it’s of an extraterrestrial origin.”
The following month the Roswell case happened when the air force issued a press release about finding a crashed flying saucer before back tracking to say it was a weather balloon.
Behind the scenes the FBI took these cases seriously and investigated.
Project Sign began at the end of 1947, and later evolved into Project Blue Book.
In 1950 Hollywood released the film The Flying Saucer – which was the first time an alien ship was depicted as a flying disc.
In 1951 The Day The Earth Stood Still used a flying saucer to warn humanity about nuclear annihilation.
It was not until 1952 that the USAF came up with the term unidentified flying object (UFO).
The 1950s became the golden era for UFOs with cold war paranoia fuelling sighting after sighting.
Nick Pope, who once investigated UFOs for the Ministry of Defence (MoD) said: “On 24 June 1947 a pilot, Kenneth Arnold, saw strange objects that the media dubbed ‘flying saucers’. “This marked the genesis of the modern UFO mystery.
“Now, almost exactly 70 years later, the UFO mystery lives on and there’s still huge interest in this fascinating topic.”