Project Blue Book Case #907. On March 13, 1951, an unidentified object was observed over McClellan Air Force Base near Sacramento, California. McClellan was a major Air Materiel Command logistics and maintenance depot — and, notably, the base that housed the Air Force's intelligence operations for the Pacific region.
McClellan AFB processed intelligence data from across the Pacific theater, making it a sensitive installation where security clearances were high and personnel were trained in the careful observation and documentation of unusual events. The base also handled maintenance and overhaul of aircraft from across the western United States, meaning its personnel had hands-on familiarity with virtually every aircraft type in the inventory.
March 1951 was during the Korean War, when Pacific-focused intelligence operations at McClellan were at peak activity. The base was processing reports from combat units, reconnaissance missions, and signals intelligence operations across the Pacific. Any unidentified object over this intelligence hub demanded serious attention.
Sacramento's position in the Central Valley provided clear conditions for aerial observation, and McClellan's multiple runways and busy flight operations meant there was no shortage of conventional aircraft for comparison. The object observed on this date did not match any of them.
The case was classified "Unknown."