So the Germans are attacking my Caribbean convoy and my Canadian convoy, since they are not as heavily defended. My destroyers in Bristol failed the interception roll, so the subs continue unmolested.
Even though both subs are attacking the same sea space, because there are 2 convoys, he has to choose which subs will attack which convoy. He chose to attack my Canadian convoy with 1 sub, and my Caribbean convoy with 2.
In the Canadian convoy, he rolls a 3 (hit), and my destroyer rolled a 5 (miss). All sub hits can only be applied to transports, not destroyers in Strategic Warfare, so I lose the transport. In the Caribbean convoy, he rolls two 2s. Both hits, but destroyers cannot be hit, so only my transport is lost. I roll back a 3 (hit), so he has to lose a sub. Strategic Warfare is over, so he returns to port.
Luckily, I have extra transports to fill the convoy when it is my turn, so I can keep the money and supply flowing. He has 2 subs coming on the board, so his losses are replaced as well.
I will add more destroyers to these convoys to keep him from attacking these.