English: Simplified drawing representing the principles behind an acoustic torpedo. Each side of the torpedo listens to underwater sound. When the sound level is higher on one side, the control will automatically activate the rudders to either turn left or right. The torpedo will then point towards the target. The German T-5 (WW2) torpedo had three states without intermediate levels: full left/full right/straight on. Further versions of acoustic torpedoes would use intermediate actions to avoid snake-like trajectories, as well as rudders acting on vertical and horizontal plane (controlled via four acoustic detectors).