My sons and I have played AA for 10 years or so now. We began with the original version, then AA50 and purchased 1940 2nd edition Europe & Pacific in Nov of last year.
We recently adopted a new house rule for submarines that I wanted to share with this forum.
After purchasing new subs or if existing subs are not used in combat or in a SZ for convoy disruption, a player may choose to submerge or hide a sub and remove from the board & move it any number of legal spaces. As we are family, we use an honor system and simply write down the SZ number moved from & to or in the case of my sons they keep track on the iPads.
The theory is to provide an element of surprise and increase subs value especially late in the game.
For example, if US buys 2 subs in Pacific, on the next turn US player can remove subs from SZ10 write down SZ the subs have moved to and place them in the corner of the board. We use the ‘mobilization zone’ on the PAC board as the sub pen. Once a sub is used in combat or convoy disruption it remains visible on the board until the next round where the player can choose to move/submerge it into a different SZ.
As you can imagine, Germany can benefit by having one or 2 subs in Atlantic that the Allies have to account for but not really know where they are. Same goes for UK & ANZAC in the South Pacific. And even Japan can move sub down to New Zealand in 2 turns unbeknownst to ANZAC & kill any new unprotected transports ANZAC places off Sydney (my son has done this to me twice in recent weeks!!)
In tournament play or if there is concern that the honor system would not work, one could use a small slip of paper for each sub to write down SZ and place the paper under the sub.
We have used this house rule in 3 global games & have found that it adds another level of strategy & has also increased sub purchases in mid to late rounds.