[Paul Riley]

Going back to the issue about range,the best and probably most efficient way to get range is to first get yourself into a good position ahead of the target,calculate its future course from your plot markings and extend the line say 25km or so,get yourself well ahead of the target into your attack position,make a point from your UB to the target course line,measure,and there,you have a good range estimate,unless of course the target has changed course or is struggling in rough sea,he could veer a few 100m from his track.Calculating range on the fly is difficult and then estimates will be needed,but you can make life easier by maintaining exact course and speed with the target and make a plot for your UB to the ship and measure,and the distance should be constant,then fire when you have a good angle on his beam.
As has already been said,range is only really important with angled shots,and steep angles at that,90 degree bow shots range is irrelevant.
Speed of the target is the most vital piece of data,getting it wrong causes your torpedoes to pass either fore or aft of your intended spot.And I tend to favour the fixed line method for getting speed,maintain course,and change your speed until his bow is constant with your crosshair's vertical line.This is difficult in rough seas mind,an average will be needed if you intend to still attack.
I ALWAYS (unless against very fast ships in which case a running perpendicular attack will be needed) set up well in advance of the attack with all the attack data known and put into the TDC,and set up attacks on MY terms,at a predetermined spot and range (in ideal conditions).And also make sure you observed your target prior for a good 30mins or more to be ceetain of its course and speed etc.