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1947 – 1969 · Run B #169
The file system every local case below is checked against: in the summer of 1947, beginning with Kenneth Arnold's sighting of 24 June 1947 over the Cascades, the United States received its first great wave of “flying saucer” reports — over 800 reports made publicly in five weeks, by the wave's own chronicle — and the Air Force answered with a standing investigation in three successive forms, headquartered at Wright-Patterson Air Force Base in Ohio. Project Sign ran from January 1948 (authorized 30 December 1947) into 1949; Project Grudge, its scaled-down continuation, followed; and Project Blue Book, ordered in March 1952, ran until the Secretary of the Air Force terminated it on 17 December 1969. Across the three projects the Air Force investigated 12,618 reports; 701 remained officially unidentified when Blue Book closed — 303 of them from the single flap year 1952, which alone produced 1,501 reports. The records were retired to the National Archives in 1975 (Record Group 341; the case files as microfilm publication T-1206), each file holding the observers' reports, the correspondence, the press clippings, and a record card stating the Air Force's own evaluation. Those evaluations — explained, insufficient data, or unidentified — are the verdicts this section prints. Nothing here rests on a retelling where a file exists.
Air Force fact-sheet figures as carried in the Department of Defense UFO packet (12,618 sightings, 1947–1969; 701 unidentified; the year table: 1952, 1,501 reports and 303 unidentified); National Archives record statement (Record Group 341, microfilm T-1206, transferred 1975); Project Sign's authorization and dates from the Sign final report (project number XS-506, 22 January 1948, under the Deputy Chief of Staff letter of 30 December 1947).