Project Blue Book Case #2388. On February 4, 1953, a bright object was observed over Yuma, Arizona — the second Blue Book unknown from this desert weapons testing hub (the first being Case #1310 from June 1952). Yuma's combination of the Army Proving Ground and the Marine Corps Air Station made it one of the most heavily used military test areas in the country.
The recurrence of unknowns at Yuma — separated by eight months — suggested the testing range area was either a genuine focal point for anomalous activity or a location where unusually attentive military observers produced more reports than average. Either explanation was significant.
February 1953 was in the post-Robertson Panel period, when Blue Book was under pressure to find conventional explanations. The Yuma case survived this scrutiny.
The object did not match any test flight, weapons launch, or training exercise at either the Proving Ground or MCAS Yuma. The case was classified "Unknown."