sonar torpedoes are usually red at the front. they were something extraordinary for WWII because they could follow an enemy and a wolf (sub) did't need to take a perfect position to hit a ship.

they are electric as far as I know the do as much as 30 kts and a max depth of 25 m.

There is no need to 'mod' them into your career. At the appropriate date (If you are using the Grey Wolves Expansion.) they will become available to you in your office menu between patrols.

ZK2's are really perfect for self-defence. But his speed is around 23 knts, and nothing more. My usage is mainly, if I'm spotted. The Destroyer comes often toward you at a speed over 30. My tactics are, I let him come straight against me, full abeam.(Crazy Ivan). ZK2 armed, running depht to 2.5 meters, and at 2000 meters distance I release the eel. At this very moment I dive to 19 meters and all silent. As soon, as the destroyer does not hear your noise anymore, he will slow down trying to spot you again. Meanwhile, the torpedo closes in on him, eventually he passes by astern, but will now make a turn and will home in on the destroyer, which is actually at a speed of approx. 16knts. The eel WILL hit him. Most of the time, propellers and rudder are blown away, besides the big hole at the stern. Sometimes the destroyer does not sink immediately, but at least, he is no threat for you anymore.
So far my experiences wit accoustic torpedoes.

Marcel, as KptLt. Heinrich "Ajax" Bleichrodt