Unfortunately Werner Sobe's video tutorial on the subject seems to be inactive, but although I never carried out a sonar only attack myself, the theory behind it is fairly simple. Once your sonar operator gets a target, have him repeat the bearing during the attack. He will notify you, if the target is closing or moving away. For obvious reasons we will need the target to be closing.
Once the target is within approximately 4000 yards, we can plot its position on the map using active sonar. Go to sonar station and press 'Range to target'. The range will not be exact, so you will need to press it over and over and try to estimate the average range from your observations. Once you are satisfied with your range estimation, go to the map, start chronometer and make your first plot. Repeat this procedure every 5 minutes or so and try to estimate target course from your observations. After a while you will also be able to estimate target speed using chronometer. Now all requirements are met to set up a firing solution.
Go to periscope and input speed and AoB into the TDC.
Move your sub into a good firing position. When the target is within 2000 yards, your range observations will be more accurate. Just before the attack, go to sonar station and send range and bearing repeatedly to TDC using the buttons on command bar. Launch torpedoes and cross your fingers
