Production of naval units modified by available harbour facilities
Just a thought, I have no idea if it would be worth the trouble:
Would it be possible to somehow link production time of naval units to the amount of naval bases available?
Retooling of the production line somewhat covers it, but only the production of the parts themselves, the actual building of the hulls requires huge dry-dock facilities.
It could be great if it was possible to somehow add the combined levels of naval bases owned by a country, and based on that giving a bonus or a penalty to production time of naval units. Perhaps modified by how much IC is currently used in ship production.
I know that Germany, for instance, would be hit quite hard by this, prewar, but after conquering the harbours of Denmark, Norway, the Netherlands and France they should see quite an increase in ship production times, even with a "occupied country" penalty. This would also make occupying Norway and Denmark worthwhile (I never attack Norway as Germany, more useless territory to defend - Denmark however, is great for blocking the Baltic sea)