I assumed it must be with the acoustic T5 type only.
Am I right?
You may attack an escort with normal torpedoes as well. You may use the T5 Zaunköning (Wren)torpedo for a bonus against escorts. Historically the T5 was equipped with an acoustic homing device that was tuned to follow the higher-energy sound of the escort's screws (as opposed to the lower frequency of the merchant ships). The T5 was soon countered by the Allies by the use of "Foxer"; a towed noisemaker that fooled the T5.