Satellites would transform wartime naval reconnaissance

How would the Second World War change if an Allied power had satellite navigation?

Dramatically; the same capability would likely bring satellite communications and reconnaissance that exposed fleet locations and port activity.

The guided-shell hypothetical extends far beyond navigation. A state able to place and operate GPS-like satellites would probably also possess satellite communications and orbital imaging. Even intermittent photographs of major naval bases could reveal whether important ships were present without risking reconnaissance aircraft. That information would change searches, interceptions, and the timing of operations across the war. The wider space-based intelligence system would matter more than accurate navigation alone.