Heibges's method has some draw back though...
For the speed calculation you need to match the speed of your target on his own course. Actualy if you have some enemy's activities around it s not that simple... expecialy if your target is moving 8 knots or more...
Then for the range calculation you need to be at his perpendicular. The projected lenght is the actual lenght only at the perpendicular. That s why we used height actualy
without the contact update on nav map (which is giving you the real range automaticaly actualy), having an accurate range is THE central piece... with range and bearing at two times, you have heading and speed. Still you need to get that damn range
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Don t forget, the close you are, the less inacuracy is important. The range of your shot should not be determined by your shot, nor by the chance to be spoted before firing but by the time the escort will need to be on you