I don't remember if it's already been mentioned, but I'd like to suggest this:
- Ground and Sea AI able to do some kind of "dodging" when enemy air units are around (maybe not ground AAA units, and not necessarily intelligent evasive manouvers, but taking the same heading as a torpedo plane approaching or some kind of zigzag when a dive bomber approaches)
- Ships AI should identify other ships so they don't collide
- Ship groups, something like ground columns. Example: Small convoy, Medium Convoy, Large Convoy, Carrier Group, etc.
I know it's a hell of a modification to ask, but it would be awesome to have these modelled.