Additional question: what were the methods for stopping a leak? In Das Boot there was a scene where they used wood beams to stop a leak. Seemed far out.

Follow up question: In U571 a Lieutenant says "Step away from the bulkhead. The shockwave (from depth charges) from one of these explosions could snap your spine." and later "One came so close it rattled 4 teeth out of the skippers skull."

Is this just hollywood fantasy? Or were there documented cases of things like this happening? Did depth charges really rattle the crew of a sub that hard in ww2?

Wow, that's a lot of deleted comments. In any case, old WW2 era diesel-electric submarines, including the U-96 from Das Boot don't fall into the image of what a layman thinks when he says 'submarine'. These boats spent a majority of their time floating on the surface, and their performance underwater was limited by low speed and maneuverability, depth charge vulnerability and minimal situational awareness. As such, the diesel-electric subs of the era weren't designed to either dive to great depths or stay underwater long - this was mainly a design feature meant for evasion - most u-boot attacks happened on the surface, and most of them used their 88mm deck gun on unarmed merchant shipping - only later (1941) when the escort system was fully implemented and british inventions like ASDIC and Hedgehog, and their higher usage of scouting planes like the PBY Catalina, made submarine warfare a lot more dangerous, has this changed.

As such, diesel-electric submarines were designed to dive to a maximum depth of 150 meters - measured at the waterline which amounts to a pressure of 16 atmospheres. Also, what you see on the outside of the submarine is not what's taking all that pressure on. Submarines had two hulls, an outer hydrodynamic hull that allowed for its maneuverability, and an inside, cylinder-shaped reinforced pressure hull, designed to withstand the aforementioned hydrostatic pressure.

Now let's get to the matter at hand - the rivets flying out of their joints and water spraying through them as in Das Boot - unfortunately this is not realistic and is only here for the dramatic effect - in case a single rivet flies off, that means your sub's structural integrity is weakened and has reached a critical point - it's definitely less resilient than before (when that rivet was in its place), and the water pressure stays the same - meaning you've passed the critical point of pressure and you're likely to suffer a hull collapse in the next few seconds.

But that doesn't make for good suspense in cinema, does it?

I suppose this cinematic feature comes from copying of how flooding damage looks on surface ships - a surface ship damaged by an underwater explosive device like a torpedo or a mine, will start taking on water, and at any point under the waterline, it will be under considerably more pressure than the air inside the ship's bulkhead - this means rivets loosened from the explosion beforehand flying off due to water pressure, water spraying through small leaks and such. However, surface ships don't have 16 atmospheres of pressure above them that would crush them if this happens and there's numerous examples of ships managing to control flooding damage and living to sail another day (most famous probably being the case of USN New Orleans at the Battle of Tassafaronga).