They slowly started to have them, at the end of the war, but they weren't that popular: using the radar reveals the sub's position, nullifying its stealth advan

They slowly started to have them, at the end of the war, but they weren't that popular: using the radar reveals the sub's position, nullifying its stealth advantage. There were also acoustic torpedoes, and all subs had passive sonar (the one you can listen to, I'm sure it's in SH3). The XXI supposedly had an active sonar for torpedo targeting, but Germany had barely started making them at the end of the war, and again using it is like yelling your position.