After much thought and discussion, we have decided how we will treat ocean-facing, Kriegsmarine batteries. They will be portrayed on the game map as infantry units; this portrayal represents the defensive capability of the guns crews and on-site support personnel. The Allied Naval units assigned the mission (historically) to the neutralize these sites will not appear as available Naval Assets (for player employment) until their assigned Kriegsmarine battery target was "disappeared" (historically), as threats to Allied naval operations.
We did consider the creation of a Counter-Naval game engine along the lines of the current Counter-air system...shore batteries vs naval assets, RADAR, SONAR, U-Boats, E-Boats, Anti-naval Air, Weather and Sea States...but set these thoughts aside as high-complexity, low-value additions to a ground-oriented game. IOW, don't start a good ground game with a complicated set of Naval rules rules that will only be in effect for a few game turns. Good scenario design will account for the impacts of the naval war on the ground war.
