[Skybird]

1944, Type IX, patch 1.4b, realism 90-something percent

Learn for how long you can travel on battery on low speed. At slow speed that translates into something like 80-90 km, and still reserves left. Mark that distance in the center of danger, in the street. Make a surface approach at night to the starting point of that line, then dive as deep as possible and travel the whole distance at day, make maximum use of your batteries and oxygen supply. Don't exceed the lower speed settings. Take care of raising ocean floor, don'T crash into it. stay at 150-200 m for the most. When you are forced to come up again, 12 hours or so will be over, probably it will be already dark again, and the street already lies behind you.

Did that four times with destroyers constantly patrolling, never had no problem. In fact it was so boring that after the fourth passage I ignored the Med from that on.