[Hooston]

Ah yes, I vaguely remember the aircraft get a bit silly in vanilla. If I remember correctly they are also absurdly easy to shoot down, but eventually they will get you. A good reason to switch to GWX or NYGM.
Don't use TC>256 in areas where aircraft are about. Crash dive immediately the aircraft is spotted and as soon as the boat is at 10m start to turn. Unlike real allied ASW aircraft the depth charges they drop are still a threat at moderate depths; you are fairly safe at 50m.
When you have been spotted or have sent a radio message you are much more likely to get attacked by aircraft for the next day or so.
However remember the game expects to kill you in the mid war period. I've never got past mid 1944. In fact the game gets slowly worse as a simulation as you get towards the end of the war because the real life equipment and tactics became way more complex.