A "ship" in SH4 will be destroyed when it comes into contact with a "land mass", so the tanks do the same thing. A "platform" for them is just something that they can sit on to keep the from "contacting" said "land mass". Not dark magic, just misplaced technique that has been forgotten. But we'll find it...
The shore batteries are not destructible. If you put a BB off-shore from gun emplacements, they will eventually sink the ship, and be able to take on more. The guns are not very accurate against AI controlled ships though. The set-up is like that more to entertain the player, and draw his eye away from the problem that the earth doesn't lift when a naval shell strikes...
- but really, it's all just for show, or "immersion" as it's called. There could also be a "destructible" version of some of the gun emplacements, so that a person could "see" the massive destruction brought about by bombardment of the Kongo on Guadalcanal... only problem being is "where is that confounded gun emplacement anyway?"...
