Bigger coastal guns cannot cover every landing site

Would Germany have been better served by 11-inch or 15-inch coastal guns around Normandy instead of 9.4-inch weapons?

Larger guns would be more dangerous locally, but fixed defenses still face an attacker who chooses the landing site and can concentrate greater force there.

Fifteen-inch weapons would pose a serious local threat, and even 11-inch guns matter when supported by effective fire control. The defender's deeper problem is geographic: fixed batteries cannot know where the landing will occur, while the attacker can mass ships and aircraft against the selected sector. Initiative and concentration of force matter more than caliber alone.