Let teh AI crew shoot at planes. I built up the following quickly:
Spent Renown on AA gunner and Sonar.
When your crew spots or the radar does, wait and change direction on the plane as well.
Tell your gunner to FIRE AT WILL on PLANES ATTACKING SUB.
Last mission I was on, I scored 15 planes shot down and didn't take a single dent.
I gave my gunner a medal and a promotion and now he is like at a 120 for gunnery and hits targets at insane distances.