Truly hardcore? Bear in mind that to be a submarine captain you had to go through months of training in trigonometry and calculus, then several years of service as a junior officer, finally working your way up to executive officer (1WO) for the Germans, at which time you would be responsible for all the plotting and calculating. By the time you were captain you would have an instinctive knowledge of a ship's course and speed just by looking at it. The calculations would be merely to confirm what you already knew in your head.
'Submarine Captain' was a full-time job for those who lived it.
Yes, doing all your own calculations is cool, and no, I don't do it. It's beyond my capabilities. But good luck to you and I hope it works out.
