Aircraft score the vast majority of kills against me when I play SH3; the depth charge load of big bombers like the B-17 and B-24 make them extra-deadly late in the war.
In my opinion, the fact that U-Boats were ordered at one point to "stand and fight" aircraft in real life is insane. 50 men and a submarine in exchange for one plane shot down now and then? Not much of a trade.