You can read all about it here:
http://en.wikipedia.org/wiki/Squid_(weapon)
I think we have talked about this weapon in other post before here.
And iam also still wonder why this weapon didnt go into the the game coz it was quite common weapon on ships. Would be darn hard to avoid an attack from this weapon Coz its activated by the sonar when the sonar tells if a target is in the proximity.