>>538455198
I remember it taking some practice. You should ideally have gold torpedoes on all of them, upgraded to 6+. You need to kill three cargo ships and then save the rest of your torpedoes for the boss.

The best torpedoes are the gold Bidders in the Royal Navy section of the Gear Lab, if you've been farming Operation Siren for materials. The core shop has snorkels and pressure hull designs, which are good on most subs.