What is the point of it? There are currently no hard kill systems for intercepting a torpedo attack (yet) that need to be saturated. There are however decoys and other electronic countermeasures.

 

Then there is the problem of the sheer size of the weapons. A Mk.48 torpedo is 19 feet long, which is more than the external diameter of most non-nuclear submarines. So these vertical torpedo launchers will be restricted to nukes only unless you are willing to give up the size and cost advantage for conventional submarines.

 

The next problem with torpedoes is their low speed relative to the targets they are trying to intercept makes short range systems, typically less than 10 miles in a tail chase for a 30 knot target. You can fire from farther out if you can keep the enemy from detecting the attack until the torpedo is closer, but a ‘ripple launch’ vastly increases the likelihood of early detection. It is very likely that every other ASW helicopter will be on top of your position in minutes, not enough time to start a proper evasion.

 

Then you have the problem that some of the torpedoes will mask the target from the sensors on the rest of the torpedoes. Not a major problem until you have to cut the guidance wires from the sub, but a big problem once the wires are cut. And you cannot ‘slink away’ without cutting the wires.

 

Finally there is the fratricide. When a torpedo detonates if other torpedoes are too close their sensors will be deafened. Even if no torpedoes are directly damaged directly the explosion will generate a disturbance in the water that no sound can penetrate, causing other torpedoes on the same or nearby targets to lose their target lock until they penetrate the disturbance, and then have to reacquire the target, presenting the target with lots of opportunities to play tricks.

Exactly ^^ 

 

Masking a ship's signature with a soft-kill jammer is reliable because you only have to mimic a known acoustic signature to obscure the original, as a last resort you also have the option of deafening sensory systems altogether. 

 

Even jamming active sonar is relatively trivial, compared with radar for example - it's a much slower omnidirectional medium with a comparatively narrow bandwidth and energy spectrum with far more sensitivity to being deafened. It says something that soft-kill systems have been deemed adequate to date - the main point being that for torpedoes (and thus their sub's life expectancy) stealth is most important - for the target the emphasis is on detecting inbound as early as possible in order to facilitate jamming and for this reason (and the others mentioned) a massive salvo makes little sense except as a suicide mission for the sub. 

 

R