# A Modern Submarine Descends Below Crush Depth-What Happens? **URL:** \ **Category:** Factual Questions\ **Created:** [September 5, 2015, 12:28pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002 "2015-09-05T12:28:00Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [September 5, 2015, 12:28pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/1 "2015-09-05T12:28:00Z")
I mean, would it be like a WWII submarine-all kinds of valves and pipes springing leaks, with the crew running around with wrenches trying to stop them? Or would the hull just suffer catastrophic failure, with a huge implosion that would kill everybody in seconds? Have any retired subs ever been sunk by remote control (with cameras inside to see what happens)? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [September 5, 2015, 12:56pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/2 "2015-09-05T12:56:26Z")
Just guessing… Whatever was weakest gives first - certain welds, certain easily broken openings or doors to the outside. Imagine each area of the hull in turn - if it were subject to X psi of pressure, would it break? Odds are the seals around doors or the periscope, etc - would give and start at least serious leaks. Would it crumple like a ball of tin foil? From what I’ve seen of marine construction, there’s a metal frame with plates welded, riveted, whatever to it. (I’m imagining welds in modern subs, then ground smooth to minimize noise and drag.) So would the ribs of the fram buckle first, or the plates separate? I’m imagining too that some ribbing is less able to stand stress, so certain parts would buckle first. Would buckling of say, the ribs in the mid-point of the sub cause the hull to break? If so, then water pours in an the wreck looks like something hit it in one spot. If the hull is integrally strong, then the crumpling continues until something finally breaks on the hull. My guess is the former, one spot on the hull frame will eventually buckle, the hull will break open at that point and water will rush in. Once the hull is full, the pressure will equalize, and the wreck will sink relatively intact, but with a lot of high-powered rushing water damage to the contents… ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [September 5, 2015, 1:01pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/3 "2015-09-05T13:01:16Z")
There were some pretty good answers [the last time you asked this question](http://boards.straightdope.com/sdmb/showthread.php?t=553491). :dubious: ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 5, 2015, 1:04pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/4 "2015-09-05T13:04:28Z")
One trait of a truly well-designed sub would be that the crush failure is general and catastrophic. IOW, it’s designed so all its components and systems have much the same ultimate strength - no weak links, and no parts that are significantly stronger (and thus heavier and more expensive) than they need to be. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [September 5, 2015, 1:15pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/5 "2015-09-05T13:15:50Z")
> [@Xema](#): > > One trait of a truly well-designed sub would be that the crush failure is general and catastrophic. IOW, it’s designed so all its components and systems have much the same ultimate strength - no weak links, and no parts that are significantly stronger (and thus heavier and more expensive) than they need to be. But you cannot guarantee every part will fail at exactly the same point. Plus, I don’t imagine the frame being built of weirdly variable sized ribs to equalize strength - weight is nowhere near a consideration compared to aircraft design. So whatever gives first is the point of failure, but probably hard to predict. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 5, 2015, 1:36pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/6 "2015-09-05T13:36:42Z")
> [@md2000](#): > > But you cannot guarantee every part will fail at exactly the same point. Indeed. But one aspect of good design would be the ability to predict failure accurately. ---
**Author:** ![Ex\_Bubblehead](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ex_bubblehead/32/3397_2.png) [@Ex\_Bubblehead](https://boards.straightdope.com/u/Ex_Bubblehead)\ **Post date:** [September 5, 2015, 3:21pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/7 "2015-09-05T15:21:03Z")
> [@ralph124c](#): > > I mean, would it be like a WWII submarine-all kinds of valves and pipes springing leaks, with the crew running around with wrenches trying to stop them? Or would the hull just suffer catastrophic failure, with a huge implosion that would kill everybody in seconds? Have any retired subs ever been sunk by remote control (with cameras inside to see what happens)? It’s called crush depth for a good reason. It’s the calculated depth that if reached or exceeded will result in an immediate catastrophic failure of the pressure hull (implosion) that would render the crew dead in milliseconds. Don’t need to send down an old boat to test this, just look up USS Scorpion (SSN-589) or USS Thresher (SSN-593) and examine the photos. I rode sister ships to those 2 and we were very much aware when we made excursions to test depth that we were just a little over 1 boat length away from crushed beer can status. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 5, 2015, 3:57pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/8 "2015-09-05T15:57:18Z")
As the Captain in a novel once said “That is where the manufacture’s guarantee runs out.” ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [September 6, 2015, 6:10am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/9 "2015-09-06T06:10:27Z")
> [@Fear\_Itself](#): > > There were some pretty good answers [the last time you asked this question](http://boards.straightdope.com/sdmb/showthread.php?t=553491). :dubious: Busted! ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [September 7, 2015, 2:20am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/10 "2015-09-07T02:20:20Z")
> **[USS Thresher (SSN-593)](https://en.wikipedia.org/wiki/USS_Thresher_(SSN-593))** > > USS Thresher (SSN-593) was the lead boat of her class of nuclear-powered attack submarines in the United States Navy. She was the U.S. Navy's second submarine to be named after the thresher shark. > On 10 April 1963, Thresher sank during deep-diving tests about 350 km (220 mi) east of Cape Cod, Massachusetts, killing all 129 crew and shipyard personnel aboard. It is the second-deadliest submarine incident on record, after the 1942 loss of the French submarine Surcouf, in which 130 crew died. Her... ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [September 7, 2015, 3:53am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/11 "2015-09-07T03:53:15Z")
For a bit of a hijack, is the tale that the crew is incinerated due to compressive heating of the air as the sub implodes BS, or is that what really happens? Seems to me that even if the air got super-hot, it would only do so for a fraction of a second before cold seawater would be all around everyone. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 7, 2015, 5:55am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/12 "2015-09-07T05:55:15Z")
> [@Ex\_Bubblehead](#): > > It’s called crush depth for a good reason. It’s the calculated depth that if reached or exceeded will result in an immediate catastrophic failure of the pressure hull (implosion) that would render the crew dead in milliseconds. Don’t need to send down an old boat to test this, just look up USS Scorpion (SSN-589) or USS Thresher (SSN-593) and examine the photos. I rode sister ships to those 2 and we were very much aware when we made excursions to test depth that we were just a little over 1 boat length away from crushed beer can status. Surely you exaggerate. Wouldn’t the crush depth be another 500-1000’ or more below the maximum test depth? Not that being at test depth is particularly safe. If you blow a fitting and take on water, and the sub gains too much water to surface, it would sink itself down to crush depth, right? And at test depth, the hull is so compressed that a taut string goes limp, etc etc. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [September 7, 2015, 6:27am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/13 "2015-09-07T06:27:40Z")
I would expect a pressure hull failure to be catastrophic and instantaneous. Once the hull is at the limit of its strength a small failure would immediately compromise the entire pressure hull, one way to visualize it would be to put a stone arch under extreme load, as soon as one of the stones crumbles the whole thing collapses at once. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 7, 2015, 6:49am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/14 "2015-09-07T06:49:25Z")
> [@Xema](#): > > One trait of a truly well-designed sub would be that the crush failure is general and catastrophic. IOW, it’s designed so all its components and systems have much the same ultimate strength - no weak links, and no parts that are significantly stronger (and thus heavier and more expensive) than they need to be. Rather like [The Wonderful One-Hoss Shay](http://holyjoe.org/poetry/holmes1.htm). ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 7, 2015, 11:39am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/15 "2015-09-07T11:39:44Z")
> [@md2000](#): > > From what I’ve seen of marine construction, there’s a metal frame with plates welded, riveted, whatever to it. (I’m imagining welds in modern subs, then ground smooth to minimize noise and drag.) The outside is smooth, but that’s not the pressure hull. It’s a completely seperate shroud hung around the pressure hull. I’ve never seen a pressure hull, but given that they put a shroud around it, I’m guessing it’s not smooth at all. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 7, 2015, 11:47am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/16 "2015-09-07T11:47:15Z")
> [@Xema](#): > > One trait of a truly well-designed sub would be that the crush failure is general and catastrophic. IOW, it’s designed so all its components and systems have much the same ultimate strength - no weak links, and no parts that are significantly stronger (and thus heavier and more expensive) than they need to be. [The Deacon’s Masterpiece!](https://www.legallanguage.com/resources/poems/onehossshay/) > [@Oliver Wendell Holmes](#): > > Have you heard of the wonderful one-hoss shay, > That was built in such a logical way > It ran a hundred years to a day, > And then of a sudden it – ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [September 7, 2015, 12:10pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/17 "2015-09-07T12:10:38Z")
Here’s a [YouTube video](https://www.youtube.com/watch?v=7gr_muLpvUA) of a computer modeled collapse of a submarine hull. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [September 7, 2015, 1:06pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/18 "2015-09-07T13:06:55Z")
> [@Bill\_Door](#): > > Here’s a [YouTube video](https://www.youtube.com/watch?v=7gr_muLpvUA) of a computer modeled collapse of a submarine hull. That leads to other videos that show the real deal… at least with storage tanks. This one is quite impressive, but it represents at most a one atmosphere differential: This one is pretty good too: A submarine at crush depth would be under hundreds of atmospheres of pressure, it wouldn’t be pretty. ---
**Author:** ![Ex\_Bubblehead](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ex_bubblehead/32/3397_2.png) [@Ex\_Bubblehead](https://boards.straightdope.com/u/Ex_Bubblehead)\ **Post date:** [September 7, 2015, 2:21pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/19 "2015-09-07T14:21:51Z")
> [@Habeed](#): > > Surely you exaggerate. Wouldn’t the crush depth be another 500-1000’ or more below the maximum test depth? > > Not that being at test depth is particularly safe. If you blow a fitting and take on water, and the sub gains too much water to surface, it would sink itself down to crush depth, right? And at test depth, the hull is so compressed that a taut string goes limp, etc etc. Not at all an exaggeration. The exact numbers are classified but are not as far apart as you imagine. When you’re on a 300’ boat, and crush depth is only 400’ or so below test depth, that’s not much over 1 boat length away from eternal patrol. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [September 7, 2015, 3:21pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/20 "2015-09-07T15:21:07Z")
Yeah, what **Ex-Bubblehead** said. There’s design depth, test depth, and crush depth. Design depth is equivalent to maximum allowable working pressure in a pressure vessel. Properly maintained, no worries. Test depth might be 30% past that, it’ll tighten sphincters, but it’s been to that depth safely and you should be OK. Crush depth is calculated, and there’s a possibility that the vessel might fail prematurely. 100 feet deeper is an additional 6,500 psi pounds of pressure on every square foot of surface area, and there’s a metric buttload of square feet on a submarine. [Next page](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002.md?page=2)