[desirableroasted]

You've been getting some (more or less) good advice here. Rather than repeat most of it and argue against some of it, I would just throw out these five things to think about.

Consider magnetics. If you are in fairly calm weather, this is an excellent place to use magnetic pistols. You don't have to fiddle around worrying about 90 AOB, and successful magnetic hits have more stopping power.

Zigzagging. the convoy will begin to zigzag when one of these events happens: 1) a merchant ship or escort sees/hears you, 2) an escort spots a steam-driven torpedo, 3) a torpedo explodes. You can safely use steam-driven torpedoes against AI merchant ships; they calmly watch the thing and do nothing.

Greed will kill you. Convoys are like restaurants... do you want the steak? Or do you want lobster? Or do you want roast chicken? Pick one and forget the rest. Concentrating on one target greatly increases your chances and, remember, the restaurant will be open tomorrow night. And if the escorts kill you, you wouldn't have gotten extra credit, anyway.

Salvos are for chumps. Salvos are for chumps! If you can't manage two good firing solutions against your target & squeeze them off 3-4 seconds apart, then make do with one torpedo or go back to the academy. Spraying off a salvo into a convoy and hoping is just a good way to waste four torpedoes.

Don't take out an escort first. There is a reason they call us the "silent service." Why on earth announce your presence and location to everybody before you even get a decent firing solution lined up?