# What is the weakest point on a modern submarine? **URL:** \ **Category:** Factual Questions\ **Created:** [February 24, 2010, 4:54am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236 "2010-02-24T04:54:08Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [February 25, 2010, 2:13pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/21 "2010-02-25T14:13:54Z")
> [@yendis](#): > > You use a podded system like [this](http://en.wikipedia.org/wiki/Azipod) where you have an electric motor in an external pod. Then you would only need to get electrical power to the motor. > > The problem with this system is that even the smallest amount of damage will completely disable the sub since repairing the motor while underwater would be difficult if not completely impossible. Many U.S. submarines actually do have a small motorized, retractable Secondary Propulsion Motor (SPM) colloquially referred to as the “outboard.” It is lowered into position and and rotated in different directions. It is used for close maneuvering situations (like docking). ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [February 25, 2010, 3:22pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/22 "2010-02-25T15:22:15Z")
USS Scorpion, an older Skipjack class “attack” sub, sank below crush depth in 1968. > [@Observed Damage](#): > > The operations compartment itself was largely obliterated by sea pressure and the engine room had telescoped 50 ft (15 m) forward into the hull by collapse pressure, when the cone-to-cylinder transition junction failed between the auxiliary machine space and the engine room. > **[USS Scorpion (SSN-589)](https://en.wikipedia.org/wiki/USS_Scorpion_(SSN-589))** > > USS Scorpion (SSN-589) was a Skipjack-class nuclear-powered submarine that served in the United States Navy, the sixth vessel and second submarine to carry that name. > Scorpion imploded and sank on May 22, 1968. She is one of two nuclear submarines that the U.S. Navy has lost, the other being USS Thresher. She was one of the four submarine disappearances in 1968, the others being the Israeli submarine INS Dakar, the French submarine Minerve, and the Soviet submarine K-129. > The wreckage of the... ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [February 26, 2010, 6:23am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/23 "2010-02-26T06:23:05Z")
> [@Xema](#): > > Wouldn’t this require either a motor that operates while surrounded by salt water, or one that must be pressurized (with air, or perhaps nitrogen) to match the water pressure? > [@Kiber](#): > > Plus - it would leave the only means of propulsion outside the pressure hall, making it pretty much impossible to maintain. And of course, it would still require a hole in the hull for power and control cables. So - several downsides, but not really any upside. Hmmm, yes maintenance would be a problem. But besides that, I was thinking that the unit could be in its own sealed hull. Granted, the shaft would still need to be sealed, but a breach would only compromise the isolated hull and not the main hull. As for power and control cables, would it be easier to seal these than a dynamic shaft? And couldn’t power and control be transmitted by induction through the hull, precluding the need to penetrate the hull? I’m reaching here, I know, but its just a thought. But yea, the lack of maintenance access would be the deal killer. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [February 26, 2010, 2:02pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/24 "2010-02-26T14:02:05Z")
> [@Shamozzle](#): > > I was thinking that the unit could be in its own sealed hull. Granted, the shaft would still need to be sealed, but a breach would only compromise the isolated hull and not the main hull. A breach would almost certainly render the propulsion unit inoperable. While not as rapidly fatal as a breach to the main hull, this would be an extremely serious emergency that could threaten the sub’s survival. > [@](#): > > couldn’t power and control be transmitted by induction through the hull, precluding the need to penetrate the hull? Doing this efficiently through a thick metal hull looks to be extremely challenging. Not to say that sealing a shaft against 80 atmospheres of pressure is trivial. But it has been done, and made reliable. ---
**Author:** ![CutterJohn](https://avatars.discourse-cdn.com/v4/letter/c/91b2a8/32.png) [@CutterJohn](https://boards.straightdope.com/u/CutterJohn)\ **Post date:** [February 26, 2010, 2:32pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/25 "2010-02-26T14:32:34Z")
The shaft isn’t really hard to seal. About the only thing that would absolutely prevent you from stopping the water from coming in would be the entire shaft falling out. If that happens, you’ve got much, much bigger problems. Speaking from intimate experience(I once spent a very long day scraping, cleaning, polishing, and painting one of the shaft seals on the enterprise)… Pretty much there are 3 main systems keeping water out of the people space. For normal operations, there is a plain old(though very large) mechanical seal. If that fails, there is an even plainer old ring of packing, which can be tightened down to form a seal on the shaft. If both of those fail, there is an inflatable bladder that seals the shaft. However, the shaft cannot be rotated if its inflated. If worse comes to worse, and all of those fail, you would simply seal the hatch to the shaft room. Submarines may not have this last option, however. I’ve only been on one, and it didn’t… the shaft seal was in the engine room. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [February 26, 2010, 2:50pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/26 "2010-02-26T14:50:03Z")
> [@CutterJohn](#): > > …If worse comes to worse, and all of those fail, you would simply seal the hatch to the shaft room. Submarines may not have this last option, however. I’ve only been on one, and it didn’t.. the shaft seal was in the engine room. Right. Can’t do that on a submarine, because the shaft seals are in the engine room, which is one of just three watertight compartments on a _Los Angeles_-class submarine, for example (and the largest, BTW). If all of the shaft seals failed and you had uncontrolled flooding in the engine room, the sub is toast. ---
**Author:** ![kevlaw](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kevlaw/32/2281_2.png) [@kevlaw](https://boards.straightdope.com/u/kevlaw)\ **Post date:** [February 26, 2010, 9:36pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/27 "2010-02-26T21:36:23Z")
> [@CutterJohn](#): > > If worse comes to worse, and all of those fail, you would simply seal the hatch to the shaft room. Submarines may not have this last option, however. I’ve only been on one, and it didn’t.. the shaft seal was in the engine room. In my submarine, the shaft seal was, in fact, in a separate compartment from the engine room and, in fact, we did once have a leak and sealed just that compartment (with someone in it!). Trivia: We did a Maximum Deep Dive Test before every patrol and someone would always tie a piece of string across the hull at max depth to impress the newbies when it broke as the sub went back to the surface. Our max safe dive was 750ft but I believe modern subs can go 3x that. Our boat used to creak like hell at that depth. Pretty scary the first time. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [February 26, 2010, 10:04pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/28 "2010-02-26T22:04:54Z")
> [@kevlaw](#): > > In my submarine, the shaft seal was, in fact, in a separate compartment from the engine room and, in fact, we did once have a leak and sealed just that compartment (with someone in it!). > > Trivia: We did a Maximum Deep Dive Test before every patrol and someone would always tie a piece of string across the hull at max depth to impress the newbies when it broke as the sub went back to the surface. > > Our max safe dive was 750ft but I believe modern subs can go 3x that. Our boat used to creak like hell at that depth. Pretty scary the first time. In the movie “DAS BOOT”-the German U-Boat is portrayed in a very deep dive (the depth gauge reads in the “red” region). Finally, they hit the bottom-and the hull starts making all these scarey groaning noises (as the hull contracts under the great water pressure). Suddenly, there comes a series of sounds like pistol shots-and the chief of the boat explains that the sounds are of the rivets in the hull sheaing off, as the hull plates contract. is this true? Seems like the next thing would be a wall of water flooding in!:eek: ---
**Author:** ![kevlaw](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kevlaw/32/2281_2.png) [@kevlaw](https://boards.straightdope.com/u/kevlaw)\ **Post date:** [February 26, 2010, 10:42pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/29 "2010-02-26T22:42:55Z")
> [@ralph124c](#): > > In the movie “DAS BOOT”-the German U-Boat is portrayed in a very deep dive (the depth gauge reads in the “red” region). Finally, they hit the bottom-and the hull starts making all these scarey groaning noises (as the hull contracts under the great water pressure). Suddenly, there comes a series of sounds like pistol shots-and the chief of the boat explains that the sounds are of the rivets in the hull sheaing off, as the hull plates contract. > is this true? Seems like the next thing would be a wall of water flooding in!:eek: I can testify to the scary groaning but I never witnessed rivets popping 🙂 ---
**Author:** ![633squadron](https://avatars.discourse-cdn.com/v4/letter/6/ee59a6/32.png) [@633squadron](https://boards.straightdope.com/u/633squadron)\ **Post date:** [February 28, 2010, 12:40am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/30 "2010-02-28T00:40:47Z")
> [@Claude\_Remains](#): > > I’m guessing that ballast tanks, prop shafts and torpedo tubes are all very problematic. What about the hull in general? The screen doors. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [February 28, 2010, 1:26am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/31 "2010-02-28T01:26:41Z")
> [@ralph124c](#): > > In the movie “DAS BOOT”-the German U-Boat is portrayed in a very deep dive (the depth gauge reads in the “red” region). Finally, they hit the bottom-and the hull starts making all these scarey groaning noises (as the hull contracts under the great water pressure). Suddenly, there comes a series of sounds like pistol shots-and the chief of the boat explains that the sounds are of the rivets in the hull sheaing off, as the hull plates contract. > is this true? Seems like the next thing would be a wall of water flooding in!:eek: Nope, not true. Like the exploding computers of the _Entreprise_’s bridge in _Star Trek_, it’s for effect on the viewer, added drama. On a real boat, even a single rivet failing or valve/steam duct exploding would be a serious concern, esp. at 150m depth. Nevermind a whole lot of them at once. As you surmise, it means the end will come very suddenly, and very, very soon. The groaning is real however (as has already been said), and it happened during any rapid change of depth, not just when you went too far down. It’s just the sound of the hull and bulkheads contracting/de-contracting in reaction to rapid pressure changes. [QUOTE=kevlaw] Trivia: We did a Maximum Deep Dive Test before every patrol and someone would always tie a piece of string across the hull at max depth to impress the newbies when it broke as the sub went back to the surface. [/QUOTE] They did it the other way round in _Up Periscope_ : the engineer tied a taut string to the walls of the engine room, to impress the newbies when it started sagging at the old boat went deeper and deeper. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [February 28, 2010, 3:23am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/32 "2010-02-28T03:23:53Z")
> [@kevlaw](#): > > In my submarine, the shaft seal was, in fact, in a separate compartment from the engine room and, in fact, we did once have a leak and sealed just that compartment (with someone in it!). Out of curiosity, what submarine (or class of submarine) were you on? > [@kevlaw](#): > > Trivia: We did a Maximum Deep Dive Test before every patrol and someone would always tie a piece of string across the hull at max depth to impress the newbies when it broke as the sub went back to the surface. > > Our max safe dive was 750ft but I believe modern subs can go 3x that. Our boat used to creak like hell at that depth. Pretty scary the first time. > [@Kobal2](#): > > The groaning is real however (as has already been said), and it happened during any rapid change of depth, not just when you went too far down. It’s just the sound of the hull and bulkheads contracting/de-contracting in reaction to rapid pressure changes. Even on a relatively modern submarine (like the _Los Angeles_-class I served on) the hull groans when making dramatic depth changes. Pretty unnerving the first time you hear it. We also used to do the string trick. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [February 28, 2010, 5:14am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/33 "2010-02-28T05:14:03Z")
The question needs to be clarified but as a point of impact I think the horizontal plane on the conning tower would be the weakest point of contact. Hit the end of one of those and you’re going to leverage it against the tower. ---
**Author:** ![thirdname](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@thirdname](https://boards.straightdope.com/u/thirdname)\ **Post date:** [February 28, 2010, 5:34am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/34 "2010-02-28T05:34:55Z")
Can anyone tell me where the armor is thinnest on an M1A2 Abrams tank? Also, what is the frequency of the shield modulation on the USS Enterprise? ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [February 28, 2010, 9:45am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/35 "2010-02-28T09:45:21Z")
> [@thirdname](#): > > Can anyone tell me where the armor is thinnest on an M1A2 Abrams tank? Also, what is the frequency of the shield modulation on the USS Enterprise? 12.3 Megafonzies ---
**Author:** ![kevlaw](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kevlaw/32/2281_2.png) [@kevlaw](https://boards.straightdope.com/u/kevlaw)\ **Post date:** [February 28, 2010, 8:54pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/36 "2010-02-28T20:54:30Z")
> [@robby](#): > > Out of curiosity, what submarine (or class of submarine) were you on? HMS Revenge. A Polaris (SSBN) submarine. [Nice cutaway diagram of HMS Resolution (same class) at wikipedia.](http://upload.wikimedia.org/wikipedia/commons/b/bc/HMS_resolution_model.jpg) It was only 25 years ago and it drives me mad that I can’t remember the names of the compartments and that I can’t find any annotated diagrams on the intertubes. I want to say that the last compartment was the shaft room (but I might be misremembering). In another thread about submarines I claimed to work in the Sonar Instrument Space but I suspect that I misremembered that too. That’s what it was called on my previous (surface) ship. Any other Polaris submariners around who can help me? It’s funny. I can remember exactly which compartment is which because one of the tests before you earned your dolphins was to go blindfolded from stern to stem (and point out all the fire extinguishers/breathing apparatus along the way) but I can’t remember the names. I suck. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [February 28, 2010, 9:47pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/37 "2010-02-28T21:47:16Z")
I ask because it seems that a diesel-electric sub can settle down on the bottom, and be totally noiseless (unless a crew member drops a wrench). Recently, I read about an advanced Swedish D-E boat (HMS Gotland) that gave the US Navy fits-it was so quiet that it couldn’t be tracked. So, does the USN have anything to fear from non-nuclear subs? ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 28, 2010, 11:36pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/38 "2010-02-28T23:36:16Z")
> [@ralph124c](#): > > I ask because it seems that a diesel-electric sub can settle down on the bottom, and be totally noiseless (unless a crew member drops a wrench). > Recently, I read about an advanced Swedish D-E boat (HMS Gotland) that gave the US Navy fits-it was so quiet that it couldn’t be tracked. > So, does the USN have anything to fear from non-nuclear subs? My 2¢: Yes and no. Modern diesel-electric subs are much better than anything available in WW2, and they’re as capable as nuclear subs in anything but powerplant. That is a big “but” however. Diesel-electrics don’t have the global range of nuclear, nor the ability to stay submerged indefinitely. As a secondary point, if they aren’t nuclear powered they probably aren’t going to be nuclear armed either. A carrier task force expecting trouble from below is going to be screened by robust anti-submarine defenses, including one or more hunter-killer subs, anti-sub destroyers and frigates, and air reconnaissance including helicopters deploying sonar buoys. In short, diesel-electrics can be a cost-effective option for a navy of modest means and worth having, but they’re still minor league. ---
**Author:** ![Pushkin](https://avatars.discourse-cdn.com/v4/letter/p/ee59a6/32.png) [@Pushkin](https://boards.straightdope.com/u/Pushkin)\ **Post date:** [March 1, 2010, 12:05am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/39 "2010-03-01T00:05:06Z")
> [@KneadToKnow](#): > > _NCIS_ leads me to believe that the weakest point is a sonar operator with strong environmentalist leanings. Voyage to the Bottom of the Sea suggests large humanoid monsters that pop up from behind a rock from time to time. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [March 1, 2010, 2:50pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/40 "2010-03-01T14:50:30Z")
> [@kevlaw](#): > > In my submarine, the shaft seal was, in fact, in a separate compartment from the engine room and, in fact, we did once have a leak and sealed just that compartment (with someone in it!). On re-reading, I see that you actually sealed a compartment with a leak with someone in it? Do you mean to say that they actually drowned? :eek: (I remember a scene from the 1978 film [Gray Lady Down](http://www.imdb.com/title/tt0077629/), that I saw in the theater when I was 10 years old, in which a sailor was sealed in a flooding compartment. It completely freaked me out, which makes it all the more amazing that I went into the submarine service myself.) > [@kevlaw](#): > > It’s funny. I can remember exactly which compartment is which because one of the tests before you earned your dolphins was to go blindfolded from stern to stem (and point out all the fire extinguishers/breathing apparatus along the way)… We had to do the the much the same thing in the U.S. submarine force. To be more precise, we had to wear an EAB (Emergency Air Breathing) device that hooked into various ports throughout the ship. Wearing a piece of black fabric over the faceplate (to simulate smoke), we had 3 minutes or so to make it from the torpedo room up forward, to shaft alley in the engineroom lower level back aft. You had to wear the mask the whole way, stopping to plug into air jacks as needed. Between stops to plug in and get a breath, you had to hold your breath. When you went through normally closed hatches, you also had to properly shut them behind you. [Previous page](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236.md?page=1) [Next page](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236.md?page=3)