Hi urfisch,
aren't you flying on the other board?
Well - some hints to make you live a little longer:
Avoid detection!
Never attract a DD.
Before you shoot at a guarded convoy have an escape route, away from the assumed DD searching path, showing your stern.
Shoot from far out! Going into the convoy attracts more than one DD to hunt you down. Don't try to pass the DD screen past 1940.
Deploy four eels and leave for the next planned point of attack.
Turn at flank, as long as the torpedos are on their way and the watchdogs are not aware of you.
Sometimes it's not possible to avoid detection?
Stay at PD!
You double your sensors (ears AND eyes) and you keep the opportunity for action.
You have a much smaller echo surface than at 200 meters down in the deep as long as you (try to) show your stern section - your six.
The worse the weather the worse the DD sensors work at PD! In heavy fog surface, and run at flank after a DC run - as long as the DDs have no RADAR. The heavy fog is a perfect cover.
Use the DC alley! (only possible at PD)
There is a safe alley between the DC stern rollers and the K-Gun splash point area on both sides of the DD.
In the early years, whenever a DD heads for you because he "sensed" you - head for him on the countercourse. Bow to bow - at PD! When 300 meters apart turn outward at flank and when close, turn back at countercourse.
This brings you some meters off the DD course - but parallel - into the safe alley.
(The shallow DC settings may even cause damage to his stern racks! Often happens with GWX)
Stay at flank and steer staight. The DD can't pick you up in his sternsection.
Observe him through the periscope and turn accordingly to his determination. If he turns to port after the run, you turn to port too! This keeps you a little longer in his sternsection and turns you away from his circle for the next run. Now try to keep him in your six. Use the periscope carefully.
If he picks you up again, turn to his course and let him close in at you, but at a small angle to enable you to head into the safe alley.
Stay slow until he is close - now speed up to flank and turn to the parallel course after a few seconds.
Try to get into the DC alley again! This time he may do some damage, because it is difficult to get your aftsection out of his stern rack path. Do some practice to time it right and have a repairteam asigned.
Go flank and watch what direction he turns. Turn into the other direction and try to show your six again. Of course you have to fall back to silent running and 1.8 knots/~ 90 rpm in both cases, when the DD turns over his 150° AOB. That's the point his sensors start to work again.
In all cases you have the opportunity to bite back if necessary.
Getting caught by a lonely DD is not avoidable from time to time.
In the later years you'll have some bolds to spend. I prefer to use them as cover "in the direct line". Now reported a DD I don't go head to head but turn away. I sneak under the waves at flank. No crashdive! I go down to PD and watch the DD coming after me. When lined up perfectly - we are on the same course - I go down to 20 meters and release a bold.
Still at flank I come up to PD again and "keep" the bold between the DD and me.
The DD gets only one signal - it covers my escape - until the lifetime of the bold is over.
Slow down to 1.8 knots and run silent. Keep you six showing.
Watch the DD leave the scene in disappointment - but be aware of possible air support in the region.
Viel Glück und gute Jagd!