Subs are really cheap to mass produce and in wolf packs, usually 5 or 4, and are maxed out in level terms then they can sink bigger ships before the bigger ships know it (usually) I still have surface ship capabilities for naval support and the newsreels, I use destroyers usually to escort the bigger ships in case the enemy has subs of his own because the destroyers are really good at sinking subs
British=best. Duh!