"M10 lacks the punch to kill off bigger ships"
"I haven't seen any enemy ships"
Seems to me the first problem is finding targets, second problem is hitting them, after that start worrying about how many hits it takes to sink one. New to the game and "pretty bad at simulators" it strikes me that you're overdoing the challenge to begin with - RSRDC mod has fewer targets to find in the first place, and playing with full realism including dud torpedoes the first time trying out the game seems kinda masochistic. It's no fun unless it's really really really impossibly difficult?