The planes don't always detect you, even in 1944 and even in broad daylight....
It may seem that way because you only detect their radar signals when they are angling at least slightly towards you, otherwise their emissions wouldn't be coming within range of your detection gear at all and you'd never know they were there...
If you are of an enquiring turn of mind you might just stay on the surface at 1x tc and see what they do, if they're heading in on a sharp angle they will detect you but if they're not closing too fast they may not respond to the contact....
I do suggest you get the twin rapid-fire 37mm flak gun before you try this, it makes things a bit more equal, I took down 3 planes in 1944 with no damage to my boat, by letting them come to me, going to flank speed and keeping their initial attack run at about 180 degrees, killed a Sunderland, a mosquito and a wellington that way, and had a beaufighter that came within visual (but not flak) range without doing anything...
So yes they are annoying, they're supposed to be, but not impossible...
and diving as soon as you get the radar detection, and going to at least 25m wiull get you safe most times...it's uncomfortable when your sonardude picks up a warship at that moment though
