So let's just start with the first two diagrams that you posted at the top of this thread. Take it in bite sized chunks.
The first is discussing Optimum Approach Course, but it's important to note that this has a direct link to the Normal Approach Course, which you did not include.
Quote:
852. NORMAL APPROACH COURSE:
The normal approach course is directly across the line of sight. It is the best course for maintaining or gaining true bearing on the target.
853. OPTIMUM APPROACH COURSE:
The Optimum Approach Course will bring the submarine to a firing position against the Widest possible range of target actions by virtue of successfully closing targets which would be lost with any other approach course.
|
What firing position factor fortifies us against the widest possible range of target actions? Closing the range as much as possible.
The Normal Approach Course, where possible, is a Collision Course (Constant Bearing, Decreasing Range). If it is not possible, the Normal Approach Course is the Course that will get you as close as possible to the target.
The Optimum Approach Course is a collision course with a hypothetical target abeam of the actual target by an arbitrary distance. This allows the target to pass ahead of the submarine. Why do we care about that? For starters, we don't want to actually collide with our targets. Additionally, our torpedoes have a built in arming distance, we may want to stay out of an active sonar cone, and any number of other tactical considerations we might have in mind.
Now here's the thing. These two courses have nothing to do with the shooting method. They are a part of the approach, not the actual attack. The fact that the NAC appears to be a right angle in that plate is coincidental. The target's bearing during approach depends on your speed, target speed, and AOBacu. It can be acute, right, or obtuse, depending on the variables.
On to plate XVI.
This plate is referenced in the relative motion section of the manual. It shows a collision course, illustrates the concept of similar triangles, and gives a formula for determining target speed where target AOB is known and a collision course is held.
Again, the angle in this diagram is completely coincidental as LA may be acute, right, or obtuse.
Are we on the same page so far?