well the way i see it is this: three things could have happened to the sub,
1 Detected by hostile forces, and sunk!
2-5 Detected by hostile forces and forced to dive deep, endure depth charge attack and slip away after enemy gives up attacks.
6 Undetected by hostile forces, safe passage.
This would be a single die roll with no other combat rolls or actions involved, for 2-5 the sub would remain in the seazone until the owning players next turn, when it could continue on to its destination.
I would think the sub would not get to defend itself since the goal was to either escape into the Atalantic or enter the Med to attack shipping within.
A direct attack upon ships in the Gibraltar sea zone itself would require no die rolls and combat would function as stated in the rule book.
Thoes426 :evil: