what about subs not being able to stop defenseless transports? Or subs not being allowed to stay on the surface during a battle that does not include enemy destroyers?
I am not sure where you reading this from but I check the rules again for AA50 under submarine page 16 of 16, and the only thing it mentions in reference to defending submarines is that -if there is a attacking destroyer present they have to roll a defense roll and cannot use the submerge option instead. If there is no attacking destroyer then they can submerge instead of defending.
This is from the rule book: “If there is at least one attacking destroyer on the battle board, defending submarines will participate in combat during the defending units fire step of the General Combat sequence. Otherwise, each defending submarine may submerge or fire. Remove each submerging submarine from the battle board and place it on the gameboard in the contested sea zone. Roll one die for each remaining defending submarine.”
So I interpelate this as been subs can stay in a battle if they want, but they must stay if there is an enemy destroyer attacking. If you attack a sub without a destroyer then your ships must withstand a free sneak attack and remove any casulties before they get to fire. If they miss then the sub can now sneak attack again or submerge. Also remember planes canoot attack subs without a destroy to help and subs cannot attack planes so they hit only boats.
Because subs do not control a seazone, a transport can legally move in and unload ignoring the sub into an enemy territory using amphibious assault. On the subs turn it now can attack the transport. I know it seems to not make sense that the transport can move past the sub, but the transport actually does not see the sub, therfore it ignores it.
Hope this helps a little. 8-) 8-)