I remember seeing someone made a "land unit" that could be static that would give you credit when you destroyed it.
I suggested for the Modern Sub team to have know target locations for nukes, TLAMs or what have you but I don't think they're that far ahead in their project for that. For fleet boats I wonder if someone could tweak the files so that it's mobile? (For that matter I don't think a submarine would engage a tank... but what do I know you guys are geniuses I'm sure you'll find a use for it).
Edit: Linky Linky..
http://www.subsim.com/radioroom/showthread.php?t=177771