1. Both subs have the option of submerging before rolling starts. If both subs decide to fight then the attacker rolls first. If he hits @ 2 or less then the defender is moved to the casualty strip. The defender rolls next @ 1. If he hits then the attacking sub is moved to the casualty line. After the first round the casualties are removed. If both subs survive then thy repeat the same process until one or both is destroyed or one or both submerge. In the case of submerge then combat ends and both occupy the same zone.
2. I was a little confused about this as well. If you read it carefully though it says no SINGLE TERRITORY can lose more than that, not all territories affected by that sea zone.
3. Yes. Each on it’s own turn.
4. Yes because you don’t have to move out or conduct combat until your turn and the convoy disruption occurs at the end of their turn.
5. Yes. There is no combined arms on offence. An amphibious assault is a combat move. The fighter will get to roll against the UK transports @ 3 or less. After 1 round of combat the remaining UK transports can retreat one space from the direction they came from but their cargo will have to remain on the transports until their next turn. The Americans do not take part in the combat at all. If the UK transports had started that turn in sea zone 97 (for instance if they loaded them from Greece) then they wouldn’t be able to retreat and would all be auto-killed by the fighter.
If you want some clarity I uploaded a new video the other day containing all aspects of naval warfare on YouTube. It’s a long one but it explains all aspects of water based rules and tactics for Global 40. It’s called Naval Warfare 101;
https://www.youtube.com/watch?v=UHk90JKWvsc