FBI Correspondence on the Cascade Mountains Lights
Federal Bureau of Investigation
Released via FBI Vault
1949
A terse memorandum routed through J. Edgar Hoover's office concerning repeated reports of luminous objects over the Cascade Range in Washington State, two years after the Kenneth Arnold sighting made 'flying saucer' a household phrase.
Why it was classified
Air Force investigators worried that public reporting of unidentified craft near nuclear and aviation facilities could be exploited to map U.S. air defense response times.
Why it matters
It shows the FBI treating UFO reports less as a curiosity and more as a counterintelligence hygiene problem — the template for seventy years of official ambiguity.