Hmm, this is interesting thread. I've read a LOT of complaints about this, and I wondered what everyone was complaining about. It always worked perfectly for me. (Tambor class, starting Dec 1941, 20mm single AA mount)
Being stupid, I thought people were complaining the tub wall was too high so you couldn't see the horizon as the boat pitched and rocked

I never had ANY probs on my 1st 2 patrols shooting down planes no matter what the angle.
Well last night I put into Pearl after my 2nd patrol, refitted, rearmed, recruited a crew for DC, handed out promotions and medals. That's all I did in-game, no upgrades to the boat. I DID exit the game and add on a few mods while in port.
After leaving port, a plane was spotted and I manned the AA gun, and finally saw what everyone else is complaining about. My POV was
way further back from the gun than it was before, and when I rotated it, my "body" was swinging outside the tub so my view was blocked
Was working perfectly before, now I've got the same prob as everyone else!
Well I thought it might be one of the mods I put on that did it - removed EVERYTHING and reloaded the game - same problem.
So I reloaded a save during my 2nd patrol when things worked right, and guess what? Things were fine, no probs rotating the AA gun.
I then reloaded the auto-save when I entered Pearl, put to sea without doing anything, and again, NO PROBLEMS!
Then I started doing the things I'd done last time:
1) Add DC crew, put to sea - NO PROBS!
2) Add DC crew, give promotions, put to sea - NO PROBS!
3) Add DC crew, give promotions, give medals, put to sea - NO PROBS!
Finally after all that, I saved the game with all the things I'd done, exited and reinstalled the mods I put on before. Reloaded, and still NO PROBS! AA gun is working fine.
Don't ask me, it's over my head. I'm wondering if something is getting randomly "trashed" when leaving port, that might be causing this?
Or maybe it's something in one of the mods I had installed when I was in port that did it? Remember, I uninstalled all the mods before I started doing the crew maintenance work. Then put 'em back on AFTER I was done and back out to sea, and the AA working properly.
Strange, but I'm glad to have my AA back!
DH