You know thats exactly what i was wondering..... I feel like a bit of a cheat when picking off a lone merchant with the deck gun but i guess it was a viable option during the war to save torpedoes. Of course deck guns were generaly removed by late war due to increasing pressure from allied ASW

(Atlantic theatre)
One thing that does greatly counter this though is rough weather.... some patrols the deck gun is simply not a option due to constant rough seas etc
Oh and welcome to Subsim