OK, so having played a bit more of this game now, unfortunately I have to admit stealth isn’t exactly working for me as well as I thought. At least not in the way I thought it should be used.
I can’t seem to have any success with torpedoes for starters – they’re just too slow. When loading out my subs I’ve actually been maxing out on rockets. They may do less damage, but you can load a lot more of them, and, due to their speed, I have a very high accuracy rate.
I’ve beaten two levels before I even realised it by just unleashing hell on enemy subs the instant I spot them.
I’m guessing this tactic will stop working so well in later missions, but for now I almost feel like I’m cheating!