In my experience you only need two units per port to avoid AI suicide invasions. I use 3xGAR and 2xMIL+1xMP. But it's still is a lot of IC to counter an error.
In my experience you only need two units per port to avoid AI suicide invasions. I use 3xGAR and 2xMIL+1xMP. But it's still is a lot of IC to counter an error.
Generally, two divisions (composition really doesn't matter) are enough to make the AI hesitate. I've seen it invade a defended port if it has no other options, but it's an extremely rare thing. Having the ports garrisoned and a Corps with one ARM division and 3 or 4 INF divisions as a reaction force should be enough to cover all of France, at least against the AI.
I find it much easier to take out the UK as opposed to trying to build airbases and air units to defend Germany AND garrison France after the fall. Unless of course your going straight historical.