Kenneth Arnold is usually credited with ushering in the UFO phenomenon (and the term flying saucer) with his 1947 report of mysterious aircraft flying in Washington state. He was part of a search for a missing Marine Corps C-46 aircraft that had crashed near Mount Rainier the previous December.. At 2 pm on 24 June 1947 he took off from Chehalis airport in his CallAir A and headed for the mountain. Arnold was in the midst of his search when, at an altitude of just over 9000 feet, "a tremendously bright flash lit up the surfaces of my craft." Startled, Arnold searched for a nearby aircraft that may have buzzed him, but all he could see was a DC-4 airliner. His thought then was that the light was from a P-51 Mustang, then one of the USAF's most powerful small aircraft. Before he could seek out the errant (and, in fact, spurious) Mustang, saw another flash of light, coming from "far to my left and to the north, a formation of very bright lights coming from the vicinity of Mount Baker, flying very close to the mountain tops and travelling at tremendous speed." He estimated that there were nine craft at a distance of over 100 miles. "What startled me at this point was...that I could not find any tails on them." The formation was flying almost directly across his flightpath, making it easy to make a rough calculation of their speed; assuming they were 23 miles distant, they were travelling at around 1,700 miles per hour. Another oddity was the way they moved. "They didn't fly like any aircraft I had seen before...they flew in a definite formation, but erratically... their flight was like speed boats of rough water or similar to the tail of a Chinese kite I once saw blowing in the wind...they fluttered and sailed, tipping their wings alternately and emitting those very blue-white flashes from their surfaces. At the time I did not get the impression that these flashes were emitted by them, but rather that it was the sun's reflection from the extremely polished surfaces of their wings.
Arnold abandoned his search for the C-46 (it would be found by mountaineers the following month) and landed at Yakima at 4 pm. he told his story of the strange craft to a few other people and went on to Pendleton, Oregon.There, a reporter, Bill Brecquette of the East Oregonian, was waiting for him. Arnold recounted his story, which Brecquette passed on, eliding the description of their flight pattern into "flying saucer" - the very first use of the term.
Kennerth Arnold would later write about his sighting in a book, The Coming of the Saucers.