Pat- best way of dealing with destroyers is to stay away from them.
This is exactly what Doenitz sait to his boys. Do not risk the boat, and your a**e.
The torps were not designed to work on anything with hulls submerged less than 4m.
I know the magnetic torpedo was to change it, but in reality most of them didnt work anyway- especially the early batch.
Sink the lone merchies, and avoid the big boys, and you may just get lucky, and survive the war- i never did.
The furthest i went was late 1943 with well over 100.ooo t of sunk allied steel (full real, with GWX gold, manual targetting, and star navigation- when i had time
)