radintorov posted:

Nibbles the Shark posted:

It's possible to shoot a torpedo down the bearing of the contact without doing all the complicated geometry if you think it's close, especially if you're shooting back at someone else since he'll be more concerned about getting away from your return fire instead of making sure to kill you.

Also known as a "Snapshot". And nice explanation on how the target motion analysis works on a sub.
Now, some of you reading this might wonder "ok, but how do we determine the speed?". Well, there are two ways, first one which is guessing, and with a contact moving at a constant speed on the same heading it's possible if you maneuver the sub like shown in the second picture, but there's an alternative that is much better: analysing the sound the propeller/s make.
To keep it simple (also because I'm a gamer, not in the Navy), every ship has its propeller/s make a certain number of revolutions (turns) per every knot of speed they are making, so if you've identified what class the contact is, you can determine how fast it is going depending on the noise it makes.

And how do you indentify the contact class? Well, either you have a sonarman with incredible hearing or you can let a dedicated computer compare the sound the contact make with a database of known classes.