BomberH,
I had a quick firkle around to try and find a clear and concise description of the construction of the “Limiting Lines of Submerged Approach”. I failed miserably, lots of descriptions but none clear and concise. This was the best I could find:
https://www.history.navy.mil/researc...submarine.html
If you think of it as an exercise in geometry and relative motion, not dissimilar to air defence intercept geometry, but carried out in slow motion.
YS