What happens to a submarine when it submerges past its hull crushing depth?

For example, a sub that suffered a catastrophic failure and as a result begins sinking all the way to the bottom of the sea floor (miles deep). As soon as its passes the rated hull crushing depth while still sinking what starts happening to the boat?

In WW2 all sides submarines reported episodes where they went below the rated hull crush depth and survived, often with little or moderate damage.

I don’t know about modern nuclear subs.

Previous thread, with link to another previous thread:


Shark bite attack?

One thing’s for sure, we’re all gonna be a lot thinner.

Drive over a full soda pop can with your car - see what happens.

From a previous thread.

FWIW, the official crush depths given to the skippers are engineering WAGs with some margin of errors built in, so if a sub is officially rated to say 500 meters it’s not going to pop at 501. It’s still a gamble to go that deep of course (and if the boat isn’t well maintained it might pop sooner !), but needs must when the Devil drives and that.

That being said, from what I understand when the sub does reach its popping point, it crumples fast because the entire pressure hull fails more or less at the same time, so it’s not a case of one bit springing a leak and flooding the boat. It’s one second fine, the next every hand on board is chunky salsa.

Which later, much later, can be spread on spaghetti, which I understand (hah!) is a metaphor for what happens to us/matter after/if the Universe does its own Big Crush.

During WWII O’Kane commissioned a new sub. The fleet boats had a design depth of 400 feet. He took his boat deeper that 400 feet. It developed some leaks in some of the hull fittings. Gaskets leaking and things. He surfaced had repairs made making the weak points stronger. Then took his boat deeper the repaired the leaks. He kept at this until he could go down to 600 feet with no leaks.

So I would say that at first there would be small then larger leaks at hull fittings until some blew apart then the flooding would continue at a rapid rate and they hull would then give way everyone would be compressed.

They are not WAGs at all. Not even close.

The engineers guarantee a sub to a given depth and they know with certainty it can manage it. Deeper than that and they are not promising anything but as you noted it is not like they implode by going 1 meter past their rated depth.

The reality is engineers are ALWAYS conservative on paper. They have to be. You could not guarantee 500 feet down if it popped at 501. Tiny variations cannot be accounted for and they would never do that. So they engineer it to “probably ok” down to 1000 feet and in the manual say it is guaranteed to 500 feet.

Each foot past 500 is progressively more dangerous but I would but you are still solid to at least 600 feet and have a really good chance to 750 feet.

Just do not expect to collect on the warranty if you do it.

Isn’t there something called absolute crush depth where the sub actually *will *, with mathematical and scientific certainty, crush?

As opposed to “never-exceed-this-depth” depth.

There have been different definitions and some are mixed on this thread and other previous ones linked to. For example the 400 ft rating for USN WWII ‘thick hulled’* or Balao/Tench class fleet boats was test depth. The sub would be tested to that depth, so nowhere near where the hull would be excepted to actually fail. It’s not shocking therefore that it was exceeded in combat by a significant margin without failure, though of course we don’t know for sure where hulls might have failed from going too deep, under control, to avoid Japanese attacks, where the losses are simply credited to the Japanese units closest to the location and time the boats were believed to have been lost. It’s similar with 100’s of other sub kills elsewhere in WWII where the sub didn’t make it to the surface for the crew to abandon it, which also fairly often happened.

There was apparently no such thing as ‘crush depth’ rating of USN WWII submarines, a pretty thoroughly declassified area of information. Whether there are actually is for later subs is IMO open to some question. None of the dive depth numbers for recent subs are official, they are open ‘secrets’ which probably are in the ball park, but you can’t AFAIK determine (using open sources) the official provenance of the seeming convention of quoting ‘crush depths’ as 150% of test depths, or the exact definition. It’s at least nominally secret.

*thicker hull plating was introduced, secretly, as compared to that which gave the previous otherwise basically identical Gato class and pre war fleet boats a 250 ft test depth.

I’d also add that the term ‘crush depth’ implies the loss would be due to a general failure of the hull. But it’s also possible a sub going too deep would first suffer kind of localized failure, at a hull penetration by a pipe for example, which would cause more gradual flooding which resulted in loss of depth control, then eventually the hull would fail more generally. There were cases in WWII where subs suffered flooding due to local failures at least partly related to depth (though often explosions going off in the vicinity also) but still managed to maintain depth control or make an emergency ascent to the surface. In other cases subs probably failed to overcome flooding from such localized failures due to depth, and hull eventually failed more generally.

Even in peacetime cases. For example the main (though not undisputed) theory of the loss of the USN nuclear sub Thresher was a pipe failure under pressure, and a failure of emergency ballast blowing system resulted in that flooding causing the sub to descend till the whole hull eventually failed.

And they also generally have a pretty good idea of what the real value is, but you won’t get them to admit it except under dire emergency.

There was an episode of Star Trek: The Next Generation where Scotty (from the original series) made a guest appearance. At one point, he and Geordi are trapped in some dangerous situation, and have to engineer their way out. Scotty tells Geordi to pressurize a particular tank to a particular pressure, and Geordi refuses, because that pressure is listed in the manual as unsafe. Scotty replies that he wrote that manual, and to pressurize the tank.

I remember that episode. The one where they find a Dyson Sphere IIRC.

Sometimes I wish I could upvote SDMB posts. :slight_smile: