If I may be so bold, a word of advice: If you begin your career in a Type IIA with external camera, event window and realistic torpedoes etc, make an effort to learn about manual targeting (assuming you're that way inclined towards the realism/action balance).
In my experience, it would have been easier to learn immediately about manual targeting rather than develop tactics with automatic targetting solutions and then have to 'unlearn' them and relearn tactics required for manual targeting. If you haven't already, once you're confident with Stock SH3, try adding one of the supermods. These add a whole new dimension to the game!
However, Type IIA and 1939 are ideal opportunities to learn, as there's no too much punishment from escorts (as they haven't gotten wise to subs yet) and there's also lots of single merchants running around the North Sea.
A word of warning though: Watch out for neutral Norweigan ships in the North Sea at the start of the war. I keep sinking them by accident in my haste to get a good torp solution!
