On several of the quick missions I kept getting busted by the escorts before I could get close enough to fire. I would think I had sliped through the screen only to have them hit me from behind. The old "out of sight, out of mind" trap. Keep in mind that destroyers are deaf to the stern, but so are you. Dont get too comfortable, make a 45 to 90 degree turn every so often to check for destroyers behind you when you are below periscope depth. Haven't read about it that much in WWII references, but during and after the cold war it was refered to it as "clearing the baffles."
The best luck I have had in breaking through screens has been approaching below the thermocline (depends upon water temp, depth to seafloor etc. The guy calling out the depth will let you know when you have passed through it.) while rigged for silent running. Note you can rig for silent running and set your speed to whatever you want,
but if you are running faster than ahead one third the chances of them picking you up goes way up. In the control room I have a hard time determining if they are searching in my direction because of the background music. The best thing to do is turn the music off or go to the sonar station every so often to listen for pinging. The louder and closer together the pinging the closer they are to detecting you. Watch the helmsman as well. I have noticed that when they are really close the helmsman starts looking nervious and starts looking up at the celing like he expects to see an ashcan fall out of the celing.
Fighting in the shallows is another thing all together. The chance of being detected actually goes down if you can sit near or on the bottom as long as you are set to silent running. The chance of them hearing you there is low, and since you are sitting close to or on the bottom the chance of them pinging you are reduced as well. The problem with shallow water combat comes in when you fire off that MK XIV and they follow the bubble trail right back to your location. Got to shoot and scoot.
Good Luck and Good Hunting
Capn_ Sinky (aka Stinky)
O.I.C.I.C.
Officer In Charge of Ice Cream
USS Drum