The Reich gives you perfectly good submarines. There's no need to cheat. By using proper procedures and tactics and in particular GOOD JUDGEMENT you'll be ok.
Visit my website for survival tactics, convoy attack, escort evasion. I seldom need to go below 150 meters because escorts have a hard time finding me.
If you practice Brag's Wiggle-Waggle, you can be certain that nearly half the time, enemy DDs will not bother you at all.
