Shipbucket

First of all, I meant Mk 46, not Mk 48. Though I would imagine it's theoretically possible for Mk 48 to have an anti-torpedo capability too - but I'm very sure the surface-launched ASW torps have it.

As for the underwater torpedo defense - there is a very similar idea proposed in the book series Dragon's Fury by Jeff Head. BTW, it's a very awful book series. I've linked to it before (the author has the entire series available as a PDF on his own website) and Tim and I have talked about it.

As I understand it the US has been working since the early 2000s on a design for a torpedo which can be fired out of a RAM tube or quad-packed into regular lightweight torpedo tubes on surface warships with a diameter of 6.75-inches intended explicitly to intercept other incoming torpedoes, and testing was initially conducted in 2005 - 2006 at Keyport on such a system, which may be deployed in the next couple of years (unless it was cancelled and I'm not aware of it). In combination with rockets of the RBU series as a close-in support (remember torpedo intercepts would tend to be at range) and decoys, one should be able to create a layered anti-torpedo defensive belt in principle, but it is highly dependent on having powerful enough, small enough computers to allow the counter-torpedo to filter noise, and locate and stay on target against the incoming torpedo.

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"Once movement was detected, the crew attempted to raise anchor and maneuver away from the shore, but the weather and sea conditions made this difficult. By the time the anchor was raised, the ship had been pushed too close to the shore to recover." Next time, guys, grab a blowtorch.

we also have an old system as Terne ASW
http://en.wikipedia.org/wiki/Terne_ASW