[CCIP]

Submarines are generally poor gunnery platforms, and that certainly applies to AA guns as well. They're unstable, inaccurate, and most importantly vulnerable. Even when you look at you look at German U-boats in the extreme circumstances (i.e. obeying the Stand-and-Fight order, or U-Flak boats), their successes when actually confronting aircraft were poor. I believe the absolute record for any submarine against aircraft (over a career) was 4.

From the plane's perspective, even a 20mm gun is no peashooter and could be absolutely fatal. In a shootout, the aircraft was still about 3 times more likely than a submarine to be destroyed. However when you consider the cost and compliment of an average ASW aircraft vs. that of a submarine, it becomes apparent that even at that success ratio it was extremely prudent for airplanes to keep pressing. So airplanes, provided they have any kind of armament capable of actually destroying a sub, are always an EXTREME danger. Dive when able.

The one caveat to this, though, is that the best time for an airplane to attack is WHILE the submarine is diving, when it's slowest, most exposed, least maneuvarable, most likely to go to the bottom if hit, and 100% blind. So you really have to judge the distance before diving, and do it really fast. Oftentimes it is better to drive off one hostile pass on the surface, while maneuvering at speed, and then pull the plug while the plane is coming around. You don't want to get hit in the time it takes you to dive.