The best late war survival device is the snorkel.
Before that, surviving is tough. Get the best radar detector available and try to get yourself sent to the south Atlantic. Do anything you can to survive until the snorkel comes on the scene. The only thing I can recommend in the pre-snorkel days is to do a 45 degree turn when diving just as your stern goes under water. It helps. However don't dive if the aircraft is spotted close by. Go flank speed, man the flak, and take evasive action. Dive after the first bombing run.
After the snorkel aircraft are almost a non-factor. You are a true submarine. During the day I will run submerged at 40 meters on electric engines. At night I'll 'breathe' and run at 12 meters with both the snorkel and periscope up. (I don't run with the snorkel during daylight). Once in a while my man at the scope will spot an aircraft but there's always time to lower the scope and snorkel before the aircraft sees you. They won't see you easily at night. (I run RUB which I think has Jungmans snorkel fix in it. Without that there's a bug that allows planes to see you from long distances at night.)
Of course at that point you can ditch your watchmen. Make sure you have 2 men with sonar qualifications and the best device available. Stop and listen often. All of your prey will be found from listening...
The great thing about the late war are all the intersting gadgets and torpedos. Indeed with the acoustic fish you can become something of an escort hunter.
In 44 I'll often approach a convoy with 4 normal or FAT torpedos up front, and an escort killer in the stern. I'll close to 1000 meters, fire the 4 front tubes at the convoy and wait for a minute. Then I'll empty the stern tube at the nearest escort and go deep. The first 4 fish should hit just as the stern fish is getting close to the escort. At that time the escort will often speed up and the homing torpedo should then get a good lock on him. It usually takes him out. I then exit through the hole in the escort screen.
Who said the late war wasn't fun?
