When your gyro angle is near zero (angles less than 20 degrees were called "straight shooting" by American manuals) then the lead angle does not change for a target traveling at the same speed on the same course regardless of range. That really sounds opaque and is hard to understand. Try this:
Now you can see that all you need to know is the shoot bearing. Sight down that bearing and when juicy parts of the target present themselves you pull the trigger. Each shot is aimed as a specific spot on the target. It doesn't matter what the range to the target is--you will hit your spot if the target speed and your angle to the track are correct. And that, gentlemen, is what made German U-boats and a select few American sub skippers including Dick O'Kane, so deadly. Simplify! Then simplify more.
Target identification? Who needs it! Stadimeter? What in blue blazes is that doing on my boat? Toss 'em out and lets sink some targets!