It looks like the players - once again - have to take care of the game rules themselves. As v1 rules differ from the Europe 1999 -rulebook.
AACalc Patch
-
I saw someone mention earlier about sub hits coming off first.
I believe a DD changes when a Sub fires. With one, a sub fires when everything else does.
So I think a defending sub would fire in surprise strike, but the attacker sub would fire with other units if the defenders have a DD.Also in the opening fire phase, sub hits could be taken on defending subs that also fire, thus preventing a unit from not getting to fire if you have enough subs to cover the hits.