Project Blue Book Case #1700. On July 28, 1952, an unidentified object was observed over Heidelberg, West Germany — the headquarters of U.S. Army Europe (USAREUR). While Wiesbaden hosted the Air Force's European command, Heidelberg was where the Army controlled all its ground forces on the continent. Together, these two German cities constituted the dual nerve center of American military power in Europe.
July 28, 1952, was the day after the second Washington, D.C., radar events — the most famous night in Blue Book history. The simultaneous appearance of unknowns over the Army's European headquarters and the American capital extended the great wave's peak to two continents.
Heidelberg's historic university city, nestled in the Neckar River valley, was home to the sprawling Campbell Barracks complex that housed USAREUR. The castle-topped city had been deliberately spared from Allied bombing during WWII, and its medieval beauty contrasted sharply with the Cold War tension of its military mission.
The case was classified "Unknown" — adding a third major European military headquarters (after Wiesbaden/USAFE and Ramstein) to the list of facilities that reported unexplained objects.