Patrolling the seas, The Allies new where their convoys were, so Destroyer Escorts and CAP by Sea Planes were the method of detection early in the War. There was a GAP that could not be patrolled by air and the Germans exploited this. This was one of the major reasons escort carriers were developed. More German subs were destroyed by air rather than by destroyers. Once sonar became available the wolfpacks became obsolete.
I have a house rule that has the wolf pack NO for Germany and a plus 1 on the sneak attack. This is one time roll and hit or miss the German sub may withdraw. remove the casualty immediately and no counter is allowed. Only CAP can negate this. Sea Zone 107 and 117 are killing grounds and German Subs roll 2 dice. I since have changed it to YG rule, use the best result of the roll method. To counter, the Allies can use TAC Bombers to kill Submarines. You must place them on CAP duties. That means this TAC Bomber may not scramble or intercept or attack and defend. It has only 1 job, ASW to kill submarines. In my game this unit is actually a Sea Plane but for AA conversion it must be a TAC Bomber