Project Blue Book Case #3523. On May 4, 1955, an unidentified object was reported at Keflavik Airport — the U.S. Naval Air Station and NATO air base in Iceland. This was the second Blue Book unknown from Iceland (following Case #3699 from August 1955, which despite a higher case number, may have been filed at a different time), reinforcing Keflavik's status as a recurring location for unexplained sightings.
Keflavik's strategic importance in 1955 was at its Cold War zenith. The base served as the primary staging point for maritime patrol aircraft monitoring Soviet submarine and naval activity in the GIUK gap — the critical passage between Greenland, Iceland, and the United Kingdom through which Soviet Northern Fleet vessels would transit to reach the Atlantic. P2V Neptune and P5M Marlin patrol aircraft flew daily sorties from Keflavik.
The aircrews and radar operators at Keflavik were among the most experienced aerial observers in NATO. They were trained to identify aircraft, ships, and submarines at extreme ranges and in the challenging atmospheric conditions of the North Atlantic. Their inability to identify the object they observed was therefore highly significant.
Investigation through NATO and Icelandic channels failed to identify the object. The case was classified "Unknown."