this is what I did on the Global map:
Destroyers no longer block Subs or the Sub's "First Strike" capability. They are now a A1 D1 M2 +1 w/NB C5 unit. They also have 1 preemptive "ASA" (Anti-Sub Attack) shot.
When attacking a Sub, the Destroyer will fire a one time "ASA1" (hits at 1) shot. If successful, the Sub is immediately destroyed and may not return fire. If the Sub survives, it may then submerge or take its normal "First Strike" shot.
The Destroyer also has 1 preemptive "ASD" (Anti-Sub Defense) shot for combat and 1 for movement. It hits at 1 out of 10. So when a Sub attacks a Destroyer, it will undergo 1 ASD shot when the Sub enters the Destroyer's Sea Zone and 1 ASD shot at the beginning of Combat. Both of these attacks occur before the Subs First Strike.
Destroyers will fire 1 ASD shot when Subs pass through the Destroyer's Sea Zone whether during Combat Move or Non Combat Move.
When moving through or into Sea Zones containing a Destroyer, you should form your Subs into "Wolfpacks" and move them together where possible. The Destroyer only has 1 movement ASD shot and will only fire once. If you move into or through the Sea Zone separately, the Destroyer will fire each time a Sub enters it's Sea Zone.
Destroyer ASA/D shots will stack. Meaning if there is only 1 Sub and multiple Destroyers, the sub will undergo as many ASA/D shots as there are Destroyers.
Subs remain A2 D1 M2 +1 w/NB C6. Subs cannot be blocked by any Naval Vessel. Subs are now susceptible to counterattack from Fighters and Tac Bombers. When attacking naval units who have air units present, Subs will undergo counterfire from the air units regardless of the outcome of their "First Strike".
When defending against attack by air units the sub may still submerge before the attack (except for the Tac Bombers ASA shot mentioned below).
All other rules regarding Subs are unchanged.
When moving a sub through a contested Sea Zone, you must move in one continuous movement. If you stop in the contested Sea Zone you will be unable to pass through.
In addition to it's normal unit stats, Tac Bombers now have 1 ASA1 and ASD1 each. Their ASD shot hits at a 1 out of 6. It is only fired during the Combat Phase.
Added Convoy Zones and a lot more Blockade Zones. Gave some of the SZs a PU value.
Here's a shot of the Atlantic:
There is a Russian Convoy Zone in the Indian Ocean and the north Pacific as well. I find it fun anyway : )