Regardless, as we’ve dwelved down the rabbit hole here, YOU kcdzim have discovered something.
Even if the ruling is against me, then the ruling must be, that subs retreat seperately. Thereby allowing them to retreat to any zone that the attack came from. Spreading out, Or submerging in place. But I also believe you cannot submerge if there is a destroyer. Interesting.
That said. All LAND and NAVAL units follow the same retreat rules, and all AIR units follow their own retreat rules. It’s specific to class type. This would then constitute an entirely new rule, which would be:
“You cannot retreat through the straight of Gibraltar, even if you attacked with subs from that zone, if your allegiance is not in control of Gibraltar.”
However, I’m confident this arguement holds merit, and that through technical play - it is completely and legitimately possible, as currently listed by the rules.
Lastly though, in my honest opinion, the rule should change so that subs can’t go through the straight either. Then you wouldn’t have this problem - as you don’t have it with the other canal’s and straights.