[Corsair]

The year of the war is very important, you wil use different tactics at different times, but always preferably at night. Early in the war, you can with some patience get close running on the surface, decks awash if needed. As the war goes on, you must rely on longer shots or try "dead stick" approach, submerged less than 20m and silent/slow and let the convoy come over you. Then it's like with flight sims "one pass and haul ass"...
Playing DiD, I learned not to be too greedy and prefer to sink less at one time but live for another day.