By all means if you have house rules regarding submarines, post them.
The best way for a convoy system to work is if you made North Atlantic Ocean into a series convoy zones (similar to A&A:Europe). However, once you done that, you’ve made it very difficult for Germany to access these zone. It already takes one turn for a German U-boat to reach the English channel.
Here are possible fixes:
1. Place a Naval IC in France, representing the German sub pens at Lorient. This would have the specific clause of being a navy only IC (you can only build ships from it), even after the Allies take it.
2. Add a National Objective for Germany/USA/UK stating if there are U-boats in certain sea zones that player gains/loses some number of IPCs (I’m guessing 5/10). I feel this is better than physically adding convoy zones to the map.
3. Destroyers only cancel sub abilities at a 1-to-1 basis (as discussed before).
Pros:
Gives German U-boats a real chance of surviving at least one round of combat and moving into the North Atlantic the following turn.
Cons:
Fixes 1 and 2 feel like very “specific” rules tacked on to confuse new players (kind of like the 2324324 China rules). Part of the homogeneity of A&A is lost.
The Atlantic is still too small. There isn’t sufficient room for maneuver or force the Allied player into a goose chase.
Anyways, adding convoy zones to the South Pacific looks more juicy. These occupied sea zones could have the effect of negating some of Japan’s NOs. And unlike the Atlantic, the Japanese player has to make a real effort to send out anti-submarine patrols to hunt down American subs in the Java Sea.