The source reports that Kenneth Arnold said on June 24, 1947 that he saw nine saucerlike things near Mount Rainier.
“Year One had opened on June 24, 1947, when a Boise businessman named Kenneth Arnold reported seeing a chain of nine "saucerlike things" glinting in the sun as they flew at 1,200 mph – twice the speed of sound – near Mt. Rainier.”
Source: TRUE Magazine May, 1954"What Our Air Force Found Out About Flying Saucers"
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