[groomsie]

The information isn't perfect always (I've ovserved a target appraching in the scope and sound reports it as moving away, etc), nor should it be. But, decent-to-good soundmen can tell you quite a lot, especially if they have time to listen for a while (the information generally improves with time). Clues like the ones noted above (sound intensity for example) are used, but also they count revolutions on the screws and can judge speed; then factor in the relative rate of bearing change (bearing drift) with all the other information and they can make a reasonable guess as to range (ie: a high speed target with slow bearing drift and sound level is relatively constant is at longer range; a high speed target with slow bearing drift and sound level increasing is closing; a low speed target with rapid bering drift and constant sound is close and running "with" you...make sense?).

While I was a surface ship sailor, I did a lot of anti-submarine work during my time and can verify the sound characteristics of the ocean vary greatly. The submarine lives in and depends upon these characteristics to help maximize their advantages, so the sound men become very skilled at making a judgement on their own as to the speed, range, course, and type of contact. Add in the other elements (tracking party doing Target Motion Analysis is a big one) and a sub can tell a lot without even popping up the scope.

In many respects the bearing lines tell too much information if you are using them; you can pretty well nail many target locations using those alone. But there are other elements you don't get so I figure it washes out...