Kenneth Arnold reports nine high-speed objects near Mount Rainier

On the afternoon of 24 June 1947, Idaho businessman and private pilot Kenneth Arnold was flying a CallAir A-2 from Chehalis to Yakima, Washington, when he reported observing nine bright, crescent-shaped objects flying in formation between Mount Baker and Mount Rainier.

Arnold described the objects' motion as resembling 'a saucer if you skipped it across the water,' a phrase the press condensed into 'flying saucer.' He estimated their speed at over 1,200 miles per hour — well in excess of any known aircraft of the era.

The Army Air Forces investigated the report and ultimately attributed it to a mirage. Project Blue Book later carried it as 'unidentified.' Regardless of the underlying cause, the case is conventionally treated as the inaugural event of the modern UAP era and the moment a recognizable public vocabulary for the phenomenon entered American discourse.