I am rather sure, we already heard those ideas (quite a lot as I remember) but I want them so dearly I just want to remind:
u-boat pens would be a wonderful thing to build in harbour provinces
but maybe we could see a complete overhaul to the "harbour" concept?
something like harbour defences that reflects how good are ships protected from airattacks & maybe even u-boat raids (if they come into play)
or even several attributes of a harbour that can be enhanced by different buildings e.g. logistic efficiency (how quick supply and fuel of naval units can be replentished) , supply depot (how much can be stored there), supply put-through (if other units need to be supplied through this harbour), harbour security (against sub attacks, sabotage, AA against ship), sub pens (passive defence for ships/ subs),...
and: I would love to see a complete new convoy system with convoyships present on the map, that have their load (Ress, suplly, fuel) "on board" and really transport this stuff
Should include:
The loss of cargo (Ress, supply, fuel) when they are sunk
The ress are added to the pool of the receiver when (and if) they arrive ... and not instantanous as it is now
all of this should of course be automatic as it is now - no micromanagment needed