Its in the realism options when you first start a patrol or single mission.
"No stealth meter" or something like that.
Once you start a patrol your kinda stuck with your settings for the duration of the patrol. So choose wisely before starting.
After that the next thing to ween yourself off of is automatic TDC calculations. if your using it. It has nasty side effect of giving you highly unrealistic tonnage. Aka "the silver bullet effect" Since with autoTDC you can individually target certain compartments when under 1000 meters range (engine, fuel bunker,) and take out a ship with one torpedo, 99.9% of the time. (Imagine an IXD2 or XXI with auto TDC doing this.. essh).
With manual TDC you can't do that, so you'll use more torpedo's. Anywhere betwen 2 to 3 torpedos per ship excepting the smaller 2000 tonners. Those are 1 fish shots.
After that would be the Weapons officer assistance. I still use him honestly. Ill make my calc's first, then if im not feeling good about it, have him double check me.
I think the final kick in the pants would be taking off the map contact updates option. (game displays sonar contacts on the map as the lines and such that you see, which you've been probably using for plotting)
i dont think i could ever force myself to take this option off honestly.. In this regard i am a wuss
One big kink is the external camera. This gives you WAAYY too much info. But turning it off deprives you of those glamour shots of your boat. I recently edited mine a bit so i can only look directly around my boat in free cam, and not jump round from ship to ship looking at whats going on. that way i can look at my boats exterior, but not "cheat" and look at that merchant 4000 meters away while submerged and see what my torpedo's did to him and if hes stopping or still underway.... that sort of t hing.