"Submarine acoustic warfare and torpedo defence systems are designed to operate in a similar way to the above-water sensor and soft-kill suites found in the above-water domain. In essence, they must use sonar to detect, classify and localise the threat torpedo, and then deploy countermeasure effectors (to jam or decoy the guidance logic) in combination with evasive manoeuvres. For jamming the signal transmitted by the effector must be significantly higher than the reflected echo signal from the submarine to the torpedo, so the later is masked by the gain signal and contact with the torpedo is broken. Decoys to seduce torpedoes in the homing phase, transmit a deceptive signal intended to mimic as far as possible the signal characteristics associated with the real target, and so lure the inbound weapon away from the submarine."