Thanks for a great thread with so many good ideas! Love to hear if you ever got to playtest them.
I think a major problem with the subs in all A&A games is that they don’t last very long and therefore Germany never wants to spend the money on them. In reality they had over 200 subs and remained a threat all the way into 1943.
So proposals to modify based on your approach.
Convoy box markers are placed between two sea zones and counts as an extra sea zone. Its worth is 2 IPCs extra and form a chain to the capital. Example the Canadian chain is 2 Convoy boxes and connects West and East Canada with UK. If the designated source of the Convoy chain is reduced below the IPC value the bonus for the Convoy box is also reduced starting with box furthest from the capital. For example when UKs African territories are reduced below 6 IPCs the convoy closest to South Africa is reduced in value. See list below based on 1942.2.
Any sea unit except transports that enter an enemy convoy zone and ends its movement there with no enemy sea units present disrupts it, flipping it to show it gives no IPCs and requiring 1 IPC to repair. Only destroyers, carriers and fighters starting on carriers may fire at subs in Convoy boxes, and subs only fire at destroyers and carriers in Convoy boxes. Thus if no enemy destroyers or carriers are in the Convoy box, the Convoy is disrupted without combat.
Subs have the following advantages: when moving to a Convoy box they get 1 extra move. They may also when moving to a Convoy box move through enemy sea zones containing destroyers but each destroyer then get a shot of ‘1’ in one cycle of combat only with no fire from the subs. When defending or attacking in a Convoy box or in sea zone bordering a friendly IC subs may submerge after one cycle of combat even if enemy destroyers are present.
Russia’s Convoy boxes only come into play if UK and/or US pay from their IPCs and place a maximum of 2 IPCs (UK and US combined) in each of the Murmansk and Vladivostok Convoy boxes during their Purchase and repair phase. The IPCs must then be underway one Russia turn before being available at the start of the next Russia turn. Since UK and US play after Russia the first available Convoy bonus is Russia turn 3. US and/or UK may also pay to repair Russia Convoys.
Constructed ICs (not at-start ICs) that have their Convoy chain disrupted may not produce units. In normal play this will affect Japan making Convoy chains more important to them.
List of Convoy chains:
Murmansk Chain (Russia) 1 Convoy box, sz3/4.
Vladivostok Chain (Russia) 1 Convoy box, sz63/64.
Narvik Chain (Germany, Norway, Finland) 1 Convoy box, sz6/5.
Tripoli Chain (Germany, Africa) 1 Convoy box, sz14/15.
Canadian Chain (UK, Canada) 2 Convoy boxes sz10/2, sz2/7.
Africa Chain (UK, Africa) 3 Convoy boxes, sz9/8, sz9/13, sz13/23.
Indian Ocean Chain (UK, Transjordan, India, Burma, Australia, New Zealand) 3 Convoy boxes, sz34/35, sz35/37, sz 37/38.
Manchuria Chain (Japan, Manchuria) 1 Convoy box, sz62/60.
Formosa Chain (Japan, French Indochina Thailand, Kiangsu, Kwangtung, Malaya) 2 Convoy boxes, sz36/61, sz 61/60.
Java Chain (Japan, Phillippines, New Guinea, Borneo, East Indies) 2 Convoy boxes, sz37/47, sz47/48.
Pacific Chain (USA, Hawaiian Islands, Mexico) 2 Convoy boxes, sz55/56, sz53/56.
Caribbean Chain (USA, Brazil) 2 Convoy boxes, sz22/18, sz18/11.
Total Allies 12 Convoy boxes 24 IPCs (excluding Russia)
Total Axis 7 Convoy boxes 14 IPCs
The sub special abilities are designed to make them survive longer if they are used for Convoy disruption. Maybe even a viable buy for Germany. You would mainly buy them for this purpose although still useful in a normal naval combat. Thoughts?