[spacejunkie2001]

What would cause this to break apart??

[moovova]

Limpet mines...courtesy of China?

[dainbramaged]

I imagine something went bad and caused her to sink below crush depth.

[Extremely Extreme Extremist]

Aargh! The skalawags that caused me Davey Jones locker to go into her watery grave me lad!

(Puffs on tobacco pipe and adjusts eye patch)

[verum ago]

What would cause this to break apart??

Something in the hull failed, or given that it was about to do a torpedo firing drill, something in the breech of the torpedo tube failed and admitted water into the hull. Get enough water inside a submarine- or any ship- and it starts sinking. In the case of a submarine it doesn't take much, because they're designed to be close to neutral buoyancy anyway.

Then, once it sinks deep enough, the hull (if not completely filled with water, which of course takes time) will implode violently once water pressure overcomes its strength. That implosion has been seen in other steel-hulled shipwrecks to be more than enough to break vessels into multiple pieces. Additionally, impact on the sea floor of a sinking vessel has been seen to break hulls into large pieces.

Looking up the sub's specs on good ol' wikipedia and using a cylinder-shaped surface area number derived from its length and beam, at 2800' ft depth the total amount of force trying to crush the hull (inward pressure integrated over hull surface area) is approximately 2.65 billion pounds . As strong as as a ship or submarine hull is, that kind of force can result in pretty spectacular structural failures, like a steel submarine getting crumpled so violently it ends up in multiple pieces...

One can only hope the crew didn't suffer long after the initial failure. I suppose one very dim positive note about a sub that hits crush depth and fails violently is that if anyone was still alive and conscious at that point, they were spared the experience of drowning [the implosion process would have taken less than a blink of the eye].

[SaxxonWoods]

It was a bit old, was retrofitted awhile back. Perhaps something was missed or improperly done during that process.

I think they bought it from Germany.

[Honest Nigerian]

Krakken?

[Mariner]

Dove too deep, whether intentional or not.