I am noticing problems with IRAI, it seems to have taken away the destroyers ability to attack head on, right over the submarine, making most depth charge attempts useless, I have even noticed this in the story.
I do believe that the year has affect the ships ability find submarines, the German type 1934 is making attempts to bomb the enemy subs, it proves more fruitful than the soldati's attempts.
Without IRAI, the ships go head on and usually yield many hits (Speaking as the British Subs on me) It seems their tracking systems are more adept than the German and Italian destroyers in the early war time frame, but even with IRAI, the British ships never seem to land a single hit on me, I even have enough time to zig zag until I reach deeper waters to dive.
I believe that the dates may have made the AI subs more adept at tracking the enemy ships (Including my submarine) but they still fire off all ten torpedoes (I know this is unrealistic) at once, in a line and if they miss, they just keep trying to attack, but with no ammunition.