We were taught valve theory during WEM(r)s course 1988 - so it'll be after that. Had 182 as part of our section on the Cumberland. The decoys were fcuking heavy. Was most surprised when the Old Man wanted us to do a test and the damn thing worked.
If, while you are bobbing along you see 4 torpedoes heading your way, they are probably MK8s so try to get out of the way, if there is only one, thats a different kettle of err..anyway you could try telling everyone to be very quiet and throwing something that makes lots of noise as far from your target, sorry ship as possible
The current UK system is a suite of kit called Sonar 2170, combining a towed array and jammer system (to detect torpedoes, and interfere with their homing system) with expendable acoustic decoys (to send the torpedo over *there* rather than towards you).