In pre- radar times dive in daylight and surface only at night.
When they get radar on their planes your change of survival goes strait downwards.
Use the opposite tactic. Dive at night, and surface the day. So you have a chance to spot the planes visual and dive away. At night you´re lost on the surface.
Better is not to surface at all, but thats hard.
You´ll welcome every storm in the late war days.
Have you installed Real Uboat Mod or the airpower mod?
I´m happy to be in 1940 in my career, some time ago i did start a career just for fun in may 1943.
2 of 4 times i did not make it out of the biscaya bay, one time they bombed me just at the point where my escort turns away. Even did not made it to my diving point.
You´re not the hunter any more, you´re the hunted.
But their is a little change of survival even those hard times.
It happend in real too. Anyone read "Iron Coffins"? He did make it even without a snorkel equipped to his boat.