I’ve seen a search roll used, maybe in aarhe, or somewhere, where you would roll to see if you could find the enemy ships, whether subs or surface within the zone because it’s so vast, and if found, then you could shoot. you could increase it for each sub/destroyer perhaps.
Thats what we have and have always used namely the 1:1 ratio for determining how many subs are negated and also the number of rolls for search