Edward J. Ruppelt

On June 24, 1947, private pilot Kenneth Arnold was flying near Mount Rainier (Washington) when he reported nine bright objects in formation moving at great speed between Rainier and Mount Adams. He timed their passage against the peaks and estimated a speed of about 1,700 km/h, far above any known aircraft of the era. His description of the motion —'like a saucer skipped across water'— led the press to coin the term 'flying saucer.' It is the foundational sighting of the modern era of the phenomenon: the one that triggered the 1947 wave and the vocabulary we still use. Later prosaic explanations (mirages, meteors, birds) never closed it conclusively.

On 23 September 1947, Lieutenant General Nathan Twining sent General Schulgen a classified memorandum stating that "the phenomenon reported is something real and not visionary or fictitious". It is the first documented institutional assertion by a USAF commander that the phenomenon was real — the historical floor of the entire later debate.

In a 1948 TOP SECRET document, the Project Sign team concluded the interplanetary hypothesis was the most probable explanation of the phenomenon; General Vandenberg rejected the estimate and ordered it destroyed, with no documented scientific rebuttal.

Captain Thomas Mantell died when his F-51 crashed after he chased a bright object above the aircraft's safe operational ceiling without oxygen: the first documented US military fatality in pursuit of an unidentified object.

On the weekends of 19 and 26 July 1952, controllers at Washington National and Andrews AFB tracked unidentified returns over the restricted airspace of the Capitol and the White House, visually confirmed by pilots and chased by F-94 fighters. The episode triggered the largest USAF press conference since the war and catalyzed the Robertson Panel.