# 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:** 2
**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, 8:26pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/21 "2015-09-07T20:26:42Z")
> [@Bill\_Door](#): > > 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. Send the submarine down to test depth with crew onboard sounds like a really really bad idea. Umm, it doesn’t sound totally unfeasible to make a modern submarine automated or to control it with a really long cable. The crucial control stations in the sub would be mirrored on a surface ship that the other end of the cable goes to. That way you can give the sub’s hull a real test, stressing it to the maximum that you think it can safely handle without permanent damage, and not risk the lives of over 100 people. ---
**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, 11:03pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/22 "2015-09-07T23:03:21Z")
> [@Habeed](#): > > Send the submarine down to test depth with crew onboard sounds like a really really bad idea. Test depth is a submarine’s MAXIMUM designed operating depth, and, when proper procedures are followed, and all systems are in peak shape, is perfectly safe. However, just like one wouldn’t pilot an aircraft in the “coffin corner” of the performance envelope on every flight (SR-71 and U-2 not withstanding), submarines spend very little time, other than sea trials, at maximum depth. Due to the fact that it is at the edge of the envelope we were severely limited performance wise to enhance safety. In 6 years, and well over 150 dives, I saw test depth exactly 3 times. As stated before, there is absolutely no legitimate need to sacrifice a multi-million (billion) dollar piece of hardware just to “see what happens”, we (the USN) already have 2 on the bottom, so we already know what happens. > [@Habeed](#): > > Umm, it doesn’t sound totally unfeasible to make a modern submarine automated or to control it with a really long cable. The crucial control stations in the sub would be mirrored on a surface ship that the other end of the cable goes to. That way you can give the sub’s hull a real test, stressing it to the maximum that you think it can safely handle without permanent damage, and not risk the lives of over 100 people. Doesn’t work that way sparky. The people are an integral part of the system. ---
**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, 11:20pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/23 "2015-09-07T23:20:09Z")
> [@Ex\_Bubblehead](#): > > Doesn’t work that way sparky. The people are an integral part of the system. This made me curious about submarine automation, and found [this quite old post](http://yarchive.net/risks/submarine_automation.html) on Usenet: > [@](#): > > A probable contributing factor here is that the US Navy’s submarine people do not trust automation at all in crucial roles. For example, US subs have no autopilots, even though they spend most of their time at constant speed and depth. They are “flown” manually at all times. This is not so much a matter of keeping the operators alert and informed as it is a matter of complete distrust of complexity and automation in submarines. The author of that post may be famous for writing _regex_, but I have no idea if he’s an authority on US submarine design. And although the _Los Angeles_ class subs have been around since before 1986, that’s nevertheless a long time ago, and the _Virginia_ class is around now. Still, it seems consistent with your claims. Does the USN still have a deep distrust of automation on subs, to the point of avoiding an X-shaped fin configuration so that they don’t need a control mixing box? ---
**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 8, 2015, 4:33am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/24 "2015-09-08T04:33:05Z")
> [@Dr.Strangelove](#): > > This made me curious about submarine automation, and found [this quite old post](http://yarchive.net/risks/submarine_automation.html) on Usenet: > The author of that post may be famous for writing _regex_, but I have no idea if he’s an authority on US submarine design. And although the _Los Angeles_ class subs have been around since before 1986, that’s nevertheless a long time ago, and the _Virginia_ class is around now. Still, it seems consistent with your claims. Does the USN still have a deep distrust of automation on subs, to the point of avoiding an X-shaped fin configuration so that they don’t need a control mixing box? Still true today. The problem with automation is that it can only do what it was programmed to do and can’t deal with anything not already anticipated. That’s where the human element comes in. Well trained men can react much quicker and handle the unexpected, which with most casualties is the rule, rather than the exception. The Skipjack class submarines did have an autopilot, which was turned off and rendered permanently inoperative almost from the start because it kept the planes and rudder in almost continuous motion trying to keep both depth and course. This created noise, drag, kept the hydraulic accumulators empty most of the time, and was a quite uncomfortable ride above 15kt or so. A good helmsman/planesman can keep course within 0.5deg, and depth within 3 inches, usually with only a little nudge one way or the other on the stick/wheel every 30 seconds or so. The autopilot couldn’t stay within 10 times that with continuous control input, even after extensive redesign. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 8, 2015, 5:30am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/25 "2015-09-08T05:30:12Z")
Is it really true that the radiation flux from the reactor is high enough through the shielding that you can’t safely stand next to it in the reactor compartment? ---
**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 8, 2015, 10:19am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/26 "2015-09-08T10:19:44Z")
> [@Ex\_Bubblehead](#): > > Still true today. The problem with automation is that it can only do what it was programmed to do and can’t deal with anything not already anticipated. That’s where the human element comes in. Well trained men can react much quicker and handle the unexpected, which with most casualties is the rule, rather than the exception. Interesting; thanks. It seems the Russian/Soviet subs were much more aggressive in their use of automation than US subs. They did seem to have more accidents, so maybe there’s some kind of correlation there; then again, they seemed to have a lot of quality control issues in general and maybe automation wasn’t a prime factor. An autopilot really shouldn’t be as bad as you describe. That said, if there is anything “quirky” about the controls, such as slop, or hysteresis, or lag, or the like, a one-size-fits-all control system will likely not work all that great. An experienced boat captain would easily learn and account for those quirks, though. ---
**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 8, 2015, 11:27am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/27 "2015-09-08T11:27:33Z")
> [@Habeed](#): > > Is it really true that the radiation flux from the reactor is high enough through the shielding that you can’t safely stand next to it in the reactor compartment? No, one can safely stand near the reactor compartment. Yes, one received a slightly higher dose when doing so, and, if you spent an entire patrol pressed up against the RC bulkhead you might exceed your allowed quarterly dosage, it wasn’t dangerously high. For 6 years my total exposure didn’t amount to more than 6 chest x-rays worth. ---
**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 8, 2015, 11:40am UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/28 "2015-09-08T11:40:23Z")
> [@Dr.Strangelove](#): > > Interesting; thanks. It seems the Russian/Soviet subs were much more aggressive in their use of automation than US subs. They did seem to have more accidents, so maybe there’s some kind of correlation there; then again, they seemed to have a lot of quality control issues in general and maybe automation wasn’t a prime factor. They also trusted the automation to the point that the number of crew were drastically cut, thus reducing the number of hands available to handle corner cases during a casualty. > [@Dr.Strangelove](#): > > An autopilot really shouldn’t be as bad as you describe. That said, if there is anything “quirky” about the controls, such as slop, or hysteresis, or lag, or the like, a one-size-fits-all control system will likely not work all that great. An experienced boat captain would easily learn and account for those quirks, though. It was that bad. No amount of programming can match the light touch of a trained and experienced sailor on the controls. Perhaps that’s been overcome with the newest boats. I wouldn’t know, I served on the Skipjack, Permit, and Sturgeon classes during the Cold War. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 8, 2015, 12:35pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/29 "2015-09-08T12:35:29Z")
> [@Ex\_Bubblehead](#): > > No, one can safely stand near the reactor compartment. Yes, one received a slightly higher dose when doing so, and, if you spent an entire patrol pressed up against the RC bulkhead you might exceed your allowed quarterly dosage, it wasn’t dangerously high. For 6 years my total exposure didn’t amount to more than 6 chest x-rays worth. Not near the reactor compartment, I mean you open the door when the scary symbol on it, walk inside, and stand next to the reactor vessel itself. Maybe stick a probe on one of the pipes exiting or leaving it to see what it’s doing. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 8, 2015, 12:47pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/30 "2015-09-08T12:47:12Z")
> [@Habeed](#): > > … And at test depth, the hull is so compressed that a taut string goes limp, etc etc. 😕 ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 8, 2015, 12:49pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/31 "2015-09-08T12:49:30Z")
> [@Leo\_Bloom](#): > > 😕 Apparently, you stretch a string between 2 points on the pressure hull and tighten it up at surface depth. The string will be limp at test depth. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 8, 2015, 12:50pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/32 "2015-09-08T12:50:39Z")
At maximum or near maximum depth, is there anything a sub can’t do that it can at lower depths (besides dive deep :))? ---
**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 8, 2015, 12:51pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/33 "2015-09-08T12:51:52Z")
> [@Habeed](#): > > Not near the reactor compartment, I mean you open the door when the scary symbol on it, walk inside, and stand next to the reactor vessel itself. Maybe stick a probe on one of the pipes exiting or leaving it to see what it’s doing. Same thing would happen there that would happen if you tried that in a shore based nuke power plant. There’s a reason the compartment is shielded and access is tightly controlled. No one ever enters the compartment, or even opens the access hatch while the reactor is critical. At least not in 99.9999999% of normal operations. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [September 8, 2015, 12:56pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/34 "2015-09-08T12:56:28Z")
> [@Ex\_Bubblehead](#): > > Same thing would happen there that would happen if you tried that in a shore based nuke power plant. There’s a reason the compartment is shielded and access is tightly controlled. No one ever enters the compartment, or even opens the access hatch while the reactor is critical. At least not in 99.9999999% of normal operations. …Yes, but _why_. The “ex bubblehead” I personally talked to thought it was because the shielding on the reactor itself was inadequate. That the meters of clear space around the reactor itself cuts the dose down by a factor of 8 or so due to 1/r^2 law, then the bulkheads and doors cut the dose down another 2 or 4 or so (depends on their thickness and composition), so it’s only about 1/32 the dose standing in the areas the crew are allowed to stand, even if they are taking a smoke break leaning against the reactor compartment bulkhead. This has some real world implications - if we ever build nuclear-electric spacecraft, we probably won’t be able to have a reactor inside the main hull of the spacecraft at all because it will be far too heavy with all the shielding. The reactor would probably be unshielded except for a “shadow shield” and be out on a long boom away from the crew compartment. ---
**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 8, 2015, 12:56pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/35 "2015-09-08T12:56:35Z")
> [@Leo\_Bloom](#): > > At maximum or near maximum depth, is there anything a sub can’t do that it can at lower depths (besides dive deep :))? Technically, no. However, as one gets closer to the edge of the envelope certain operational restrictions come into play, such as a much lower max speed, which allows much more time to react to any casualty that might cause the boat to assume a greater depth. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 8, 2015, 1:02pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/36 "2015-09-08T13:02:39Z")
> [@Habeed](#): > > Apparently, you stretch a string between 2 points on the pressure hull and tighten it up at surface depth. The string will be limp at test depth. Isn’t this like the SR-71, which at sea level was all rattle-y and leaking through its pores, but at speed firmed up? ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 8, 2015, 1:05pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/37 "2015-09-08T13:05:42Z")
> [@Ex\_Bubblehead](#): > > Technically, no. However, as one gets closer to the edge of the envelope certain operational restrictions come into play, such as a much lower max speed, which allows much more time to react to any **casualty** that might cause the boat to assume a greater depth. Bold mine. “Casualty” can be too many things to attempt to list, right? But a mechanical (and electrical?) anomaly is understood, not just damage from battle? [eta: one of us has got to get to work. This ain’t a chat room, bub.] ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 8, 2015, 1:19pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/38 "2015-09-08T13:19:41Z")
> [@Ex\_Bubblehead](#): > > No amount of programming can match the light touch of a trained and experienced sailor on the controls. This seems a bit strange: If a human can consistently do better than an autopilot, the obvious step is to carefully record and examine exactly what the human is doing, then design a control system that closely matches this. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [September 8, 2015, 1:25pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/39 "2015-09-08T13:25:44Z")
> [@Ex\_Bubblehead](#): > > Still true today. The problem with automation is that it can only do what it was programmed to do and can’t deal with anything not already anticipated. That’s where the human element comes in. Well trained men can react much quicker and handle the unexpected, which with most casualties is the rule, rather than the exception. > > The Skipjack class submarines did have an autopilot, which was turned off and rendered permanently inoperative almost from the start because it kept the planes and rudder in almost continuous motion trying to keep both depth and course. This created noise, drag, kept the hydraulic accumulators empty most of the time, and was a quite uncomfortable ride above 15kt or so. A good helmsman/planesman can keep course within 0.5deg, and depth within 3 inches, usually with only a little nudge one way or the other on the stick/wheel every 30 seconds or so. The autopilot couldn’t stay within 10 times that with continuous control input, even after extensive redesign. SerenDipity: Russian Kanyon sub. > **[Russia Building Nuclear-Armed Drone Submarine](https://freebeacon.com/national-security/russia-building-nuclear-armed-drone-submarine/)** > > ‘Kanyon’ unmanned sub to target harbors, cities ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 8, 2015, 1:29pm UTC](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002/40 "2015-09-08T13:29:10Z")
> [@bump](#): > > 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. Like a [fire piston](https://en.wikipedia.org/wiki/Fire_piston), the air is hottest during the final phase of compression. When the pressure has equalized, the air doesn’t simply disappear; assuming the collapse happens at 2400 feet, you’ve got one or more stable pockets full of compressed air that are at ~1000 psi and 1300F. Combustible things - papers, clothing, hair, etc. - will char and begin to burn, but there’s not enough oxygen in the trapped air to completely incinerate an entire crew; the fires will burn themselves out long before that happens. [Previous page](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002.md?page=1) [Next page](https://boards.straightdope.com/t/a-modern-submarine-descends-below-crush-depth-what-happens/730002.md?page=3)