That KaleunMarco feller is on the ball! Fast and accurate! This is basically a repeat of what he mentions, with slightly different detail...
The skipper would use the periscope markings (see
Lesson Plan 1: "Up Periscope" - Distance to the Horizon, a pdf, for an example) to estimate range. The game's periscope is not real accurate with its rendition of the view. Some US skippers avoided "pinging" because the sound could potentially be traced back to them. The game does not "model" that, so you can "take over" the sonar station yourself, aim the sonar head to the heading that you know your "target" is on, and send a ping for your range. No matter the method, you would then immediately go to your nav map and make a pencil mark based upon that information. Do that twice at a given interval (3'15" is common), and you can determine the "targets" speed also. Draw a line between and beyond the two points, and you can determine course and possible intercept point - at that point in time. If your sub's sonar heads are not "aim-able" by use of the mouse, you might want to apply CapnScurvy's
Gato Sonar Bearing Fix_Stock mod, which "fixes" the Tambor, Gar and Balao boats also. You can also use the <Home> and <End> keys to rotate the heads to "aim" the sonar. For other targeting methodology, refer to Rockin Robbins
Sub Skipper's Bag of Tricks thread.
There was a "set" aiming paradigm the US skippers were trained to use prior to the outbreak of war, which stated aiming for the middle, the bow and the aft, so that you were "guaranteed" at least one hit, no matter what the target did to avoid. However, the US had a torpedo shortage from the beginning, and the skippers were admonished to use only what was necessary, usually just one, maybe two torpedoes on merchants, and were also directed to use the magnetic trigger exclusively. Did not work out too well initially, of course, as history shows...
The acoustic torpedoes you can get in-game are extremely slow, usually much slower than a DD can go. They are also weak in explosive power, and will "target" anything making noise. The game does not "model" the noise makers ships used to drag behind, but the torps can and will target your sub, if it is the loudest nearby "target", so be sure you are "quiet". Their purpose-in-life was as a down-the-throat DD attack deterrent, but have to be shot at the beginning of the attack run, so that the "target" is coming at you. The idea being that the torp would at least disable the DD's props and / or rudders.
In the stock game, you won't find any torpedoes shot at you, except maybe from planes, and the stock game has issues with "piloting" planes. The Fall of the Rising Sun Ultimate mod has AI subs, ships and planes that can shoot torpedoes at you. The Event Camera in-game will usually (not always, if there's a lot going on) pick-up the enemy shooting at you. The way to avoid an attack to begin with is by minimal use of the periscope (not always possible). The longer and / or more often it's up, the quicker the enemy will be alerted to your presence, and can then target you. The way to avoid an attack is to dive and change course, turning toward or away from the expected torpedo track. If you are shot at like that, there is no "Incoming torpedo, sir!" vocal or text warning...
As KaleunMarco says, "Welcome To SubSim!"
