How many Project Blue Book cases remained unidentified when the program ended?

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Declassified U.S. military video of unidentified aerial phenomena (UAP) — unidentified flying object Learn about an unidentified aerial phenomena (UAP) sighting from this video (known as the Gimbal video) captured by fighter pilots associated with the USS Theodore Roosevelt carrier strike group. The video shows instrument detections of unknown aerial objects, which the pilots were unable to identify, off the East Coast of the United States, 2014–15.

When Project Blue Book concluded in 1969, a total of 701 sightings remained classified as "unidentified".12

These cases were categorized as unidentified because there was insufficient information available to link the reports to a known astronomical, atmospheric, or artificial phenomenon. Throughout the program's history from 1947 to 1969—which includes the data from its predecessor projects, Project Sign and Project Grudge—a total of 12,618 sightings were recorded.21