[Pablo]

Originally Posted by geosub1978

Technology...states:

Either by echo sounder, which means that the ASW unit passes directly over the submarine, or some sophisticated sonar devices which were definitely not available during ASDIC era!

Hi!

Actually, it was possible to get a reasonably accurate assessment of the submarine's depth.

Case 1:Consider the case of a lone destroyer early in the war, as shown in the image below: a destroyer closing on a submarine will lose sonar contact when the submarine is no longer in the "searchlight" of the active sonar; however, the destroyer knows how wide the searchlight is, so a quick trigonometric calculation will tell the destroyer the depth of the submarine given the range. For example, if the range is 500 yards when the contact fades then the destroyer knows the submarine is at a depth of about 88 meters. The U-boat will now maneuver to put as much distance between itself and the last depth at which the submarine was detected.



Case 2: A late-war (1943+) destroyer with advanced high frequency "Q" and "Type 147" sonar that provides the destroyer much more precise azimuth, angle, and range to the target, in which case trigonometry provides a quick firing solution within the range of an ahead-throwing weapon such as "Hedgehog" or "Squid" which allows for a highly accurate barrage.



These illustrations are from the "Tactics" appendix of the GWX 3.0 Gold Manual, if you are interested.

Hope this helps!

Pablo