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I'm working on an idea for a novel and need to know roughly if this is possible. Ideally, the characters would be able to attach another submersible (usually used for rescue) onto the sub in the modern day, and either use a hatch or cut through the hull to gain access to a still pressurized section. Within they find forgotten weapon cache etc etc...

Could a cold war submarine that sunk about 50 years ago still maintain pressure within it? Would there be too much corrosion and pressure due to the environment? Would the depth make a difference?

If it's barely possible that probably works to my advantage as the sub could collapse around them as they recover the item. If it's nowhere near possible I'll just have them use some sort of sub arm mounted cutter to cut into a section and the weapon can be in a sealed container of some sort.

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    $\begingroup$ A sub that sinks usually sinks because there's some damage. Water got in somehow, otherwise it wouldn't have sunk. Your question is viable if the crew dogged the bulkhead hatches to the part of the sub where the DSRV (Deep Submersible Rescue Vehicle) docking hatch is located. $\endgroup$ – RonJohn Aug 27 '18 at 19:51
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    $\begingroup$ Plotwise, it seems there is no need for air inside the sub. Your characters can remain in their scuba gear, and enter the sub, explore, extract the artifacts, and escape the dangers of collapse, or even have their body or air hoses get caught or cut by rusty metal. There is scuba gear that lets divers talk to each other. Sub could collapse b/c they cut it to get in, or b/c the air they exhale created an air pocket that is pushing part of the sub up. $\endgroup$ – Bald Bear Aug 27 '18 at 20:28
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    $\begingroup$ @RonJohn A sub descends when the density of the submarine is greater than that of water. Thus, water got in somewhere, such as the ballast tanks, but not necessarily everywhere. Otherwise, the entire crew of a submarine would die everytime they want to descend. $\endgroup$ – user71659 Aug 27 '18 at 20:44
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    $\begingroup$ @user71659 if water only got into the ballast tanks, why is the sub still down there? Yes, a malfunction that let water into the ballast tanks but prevented it from being blown out would make it sink, but then what? If it rests above the crush depth, then why wasn't the just-slightly-negative boat recovered, and if below the crush depth then... it's crushed. $\endgroup$ – RonJohn Aug 27 '18 at 20:52
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    $\begingroup$ @RonJohn Because nobody knew where it was. Or they looked and couldn't find it. Argentina still doesn't know where one of theirs is today. Or it sank where it shouldn't have been, such as in enemy or neutral country waters, and a search operation couldn't be mounted for political reasons. $\endgroup$ – user71659 Aug 27 '18 at 21:02
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It's even conceivable that all ballast tanks, vents and control systems were completely compromised, and so the sub sank with no attitude controls (bow planes & stern planes completely inoperative) but some of the crew stayed alive long enough to isolate the control room & conning tower base (equivalent to the bridge on a ship or surface boat) in the hopes of radioing for help... and then the radio went kaput.

There would be the attendant corpses with the remainders of decomposition (since dried out) and all systems would be shot: the 50's and 60's subs used electrics and electronics (depending upon the years) to drive many (but not all) control systems. If they lost all batteries (and somehow miraculously didn't blow up - lead-acid batteries upon failure often evolve hydrogen which explodes in an oxygen-rich atmosphere with the slightest spark) and whatever super-high value super-secret asset they had quickly dragged through the various bulkhead hatches from the store-room to the control room whilst dogging the hatches behind them.

Salvage access could occur through the conning tower base room, as that's massively reinforced and has two specific reinforced section axes (one circular cross along the sub's main axis and one perpendicular to that) and this would both be realistic and provide your "suddenly, a collapse began" plot-point: the seams which join the conning tower perp section begin to burst percussively (high drama as nearby bolts whizz by like bullets as the section deforms) as the entire sub is sitting on a protruding ledge in a mid-oceanic trench, twelve meters below its rated crush depth (they were typically intentionally over-engineered relative to stated specs, but as the production was so hand-labour intensive, real-world failure points were... unpredictable at best) so boy you get dramatic tension!

This linked image is to a diesel-electric sub from roughly your referenced timeperiod:

enter image description here

Oh yeah - my bona fides: though I'm a tech writer who's never spent significant time in a sub, my father is an ex Royal Navy submariner. He was Sparker (Chief Electrical Officer) on a Royal Navy A-class submarine (P 422 H.M.S. Anchorite - a Vickers-Armstrong build launched in '46) just after the Second World War. For them what cares about history: he had also been a war evacuee - one of the thousands of children from the Channel Isles sent to England days before the Nazi invasion of the Isles; we were the only part of the British Isles the Nazis ever occupied.

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    $\begingroup$ Wow thanks for all the information. I'm going to have to study that all carefully but I think that's pretty much everything I need! Submarines are fascinating things. $\endgroup$ – Ross Coulbeck Aug 27 '18 at 21:37
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    $\begingroup$ Oh - on the topic of sunken subs: en.wikipedia.org/wiki/List_of_lost_United_States_submarines $\endgroup$ – GerardFalla Aug 27 '18 at 21:42
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    $\begingroup$ Ooooh yeh - one other potentially useful detail: my Dad told me there were experimental subs the Royal Navy worked on during that time using "alternate fuel chemistry" (hydrogen peroxide and diesel fuel) - and they lost a number of them to internal explosions. The Brass kept trying anyway 'cos the damned things were fast - like ~30 knots underwater headway. They were named the "Explorer" class subs by the Admiralty, but due to their penchant for exploding and going down with all hands, the sailors all called 'em "HMS Exploder". Dunno, might be useful mate. $\endgroup$ – GerardFalla Aug 27 '18 at 21:50
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    $\begingroup$ That's fascinating, another possible option to consider :) I have a cool idea relating to sub history which I'm probably going to use, but this is early stages so things might change. $\endgroup$ – Ross Coulbeck Aug 27 '18 at 21:53
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    $\begingroup$ I don't believe they could have used the radio anyway underwater. Nor whether they had acoustic communications that long ago. In the 1970's, I communicated with subs using single-sideband amplitude modulation, but the carrier frequency was only eight KHz and it went through acoustic transducers rather than radio antennae. $\endgroup$ – WGroleau Aug 28 '18 at 18:07
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Absolutely!

It's great that you said Cold War era. The Soviets actually made a submarine with a titanium-alloy hull during the Cold War era. Titanium is highly anti-corrosive, strong, light, non-ferrous, etc. It's corrosion in sea water is only slightly worse than in air, meaning 50 years is no issue.

With an intact hull, you only need to figure out why it sunk. Ballast tank issues and either propulsion or a dive plane problem would likely be necessary. With the history of Russian submarine accidents (what we even know of) due to improperly trained crews and poor engineering, it isn't a far stretch to say that crew error was involved.

Oh, and I forgot to mention that due to the extra strength from the hull material, these submarines could dive deeper, travel faster, and be less dectectable than their steel-hulled brethren, making them perfect for a mission including secret equipment or documents. A perfect fit!

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    $\begingroup$ +1 for this, especially because the greater crush depth gives more flexibility in the location of loss, especially in the Arctic Ocean, which is shallower than others and a common operational environment for submarines during the cold war. $\endgroup$ – BryKKan Aug 28 '18 at 21:37
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So fun fact, because this question assumes Hull Integrity: When building the famous ride 20,000 Leagues Under the Sea for Walt Disneyland, Walt and his engineers had to figure out how to build a vehicle that could survive being partially submerged in water for years on end without significant renovation that required draining of the Lagoon. Since there was very little in the way of actual development in Submarines at the time, Walt Disney consulted with the then current contractor building the U.S. Nuclear Sub Fleet and wound up commissioning the company to build the hulls for the vessels in fleet. The ride, though popular, was abandoned in the early 90s due to concerns over handicapped access into the subs (there was none) and required extensive shut downs to near by areas to fully remove from the park, so the ride vehicles were parked in their garage and left with little known updating or major maintenance on the vehicles.

Fast forward two decades when the initial discussion of re-purposing the ride to an updated Finding Nemo theme and one of the first discussions were the state of the ride vehicles. As Disney Engineers discovered, this was less of an issue than they had thought... they had been perfectly servicable with little investment even after all that time out of service. Even more amazing was that when Walt contracted the Navy's contractors, he was seriously investing in this ride for life. As it turned out, the contractor figured that the best way to build a boat that would mimic a submarine and could survive for long stretches mostly submerged underwater like a sub... was to basically build a sub, and they effectively constructed sub hulls with an operational life expectancy of a military grade nuclear vessel. The Subs in the currently operational finding Nemo ride are the same ride vehicles from the original ride (save a specially modified one with better Handicapped access) and have a life expectancy that will keep them in service for an additional 50 years of operational life expectancy from the early 2010s!

To sum up, if you are going for a U.S. Navy sub and it was lost above the crush depth of the hull due to something other than a hull breach, than you should expect a perfectly intact interior once you cut in. As long as you have something to keep the water from getting into your breach AND you account for possible pollutants, it should be safe to enter and grab the cache.

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    $\begingroup$ I hope FInding Nemo is more fun for kids than 20000 Leagues Under the Sea. That "ride" (I remember from my distant youth) was seriously boring and even lame. I found your discussion of the engineering of the ride much much more interesting than the (remembered) ride itself! (The autobahn ride - in the same area as the submarine lagoon - was the thing to do! That was fun!) $\endgroup$ – davidbak Aug 28 '18 at 21:05
  • $\begingroup$ @davidbak: Unfortunately I am an East Coaster, so my only Disney Theme Park Leagues experience was the Magic Kingdom version... I was really young when I remember it shutting down and remembering that the sea serpent scared me. It was only years later when I saw footage of the ride on Youtube that I realized the Serpent had the goofiest grin on its face... I remember it being hungry and mean looking... If I recall, the World version was fleshed out a bit more to alleviate the boredom. $\endgroup$ – hszmv Aug 29 '18 at 16:25
  • $\begingroup$ @davidbak: Also, I can't speak to the survivability of the the WDW fleet of Subs, as they were built in a different era and were removed and placed in a Boneyard in a back lot before two were intentionally sunk in a lagoon in the Bahama Island resort to make an artificial reef and the rest were sold. I believe the reef subs were removed as well. $\endgroup$ – hszmv Aug 29 '18 at 16:29
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The problem wouldn't be whether there was a pressurized section of the sub, it would be whether there is a Depressurized section. If the sub is submerged, that means that the pressure outside the hull is actually grater than the pressure outside (every 34' of depth being ~1 atmosphere of pressure). This actually is what is going to drive the problem, if there is a low pressure section, it will be lighter than a similar section that was at a higher pressure (Though it isn't really much different).

They would really need a hatch, as any cutting would introduce the high pressure water. Depth wouldn't be an issue except for the magnitude of the outside pressure. As for rust, the real issue here is how good of a paint job the submarine had and whether it has been damaged. The paint can protect the metal from rust if it is a good paint with full coverage. The only question that would remain is why the submarine has been underwater for 50 years without either floating or having some kind of hull breach (maybe only some sections have flooded, while others remain in tact).

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    $\begingroup$ Paint really, really struggles to protect surfaces exposed to seawater. Ask any expert on bottom paint. $\endgroup$ – Harper - Reinstate Monica Aug 28 '18 at 4:02
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    $\begingroup$ I think you meant to say "the pressure outside the hull is actually greater than the pressure *inside" $\endgroup$ – BryKKan Aug 28 '18 at 21:28
  • $\begingroup$ You can cut in--you just have to seal around the area you're going to cut first. $\endgroup$ – Loren Pechtel Aug 29 '18 at 2:04
  • $\begingroup$ @LorenPechtel That's what I was thinking :) $\endgroup$ – Ross Coulbeck Aug 29 '18 at 6:54
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Could a cold war submarine that sunk about 50 years ago still maintain pressure within it?

No.

Submarines are not designed to be left submerged for very long periods with no engines running and no power.

Submarines are not designed to be completely watertight, like any ship or boat they are designed to let in water at a rate the bilge pumps can cope with.


Submarine Trim and Drainage

In submarines as in all ships, a certain amount of water from various sources accumulates inside the hull. The most important of these sources include:

  1. Leakage at-glands around the propeller shafts, pitometer log, sound gear, periscopes, and similar equipment.

438,000 hours of even slow seepage adds up to a lot of water.

Even modern nuclear-powered submarines cannot remain submerged for that number of years.


Could pockets of trapped air could be breathable?

  1. Oxidation:

    According to A View to a Kill - can you survive by breathing in air from a car tyre?:

    Every year people die when they dive down to explore sunken ships. They find trapped air in compartments and take off their masks thinking they will be able to breath. Unfortunately over time much of the oxygen gets used up rusting the ship's metal parts and what looks like breathable air may in fact be mostly nitrogen. Divers can easily suffocate because although the air is at the right pressure and feels comfortable to breath they actually get less and less oxygen in their lungs with each breath.

  2. Narcosis:

    Air is mostly Nitrogen. At depth, Nitrogen is an anaesthetic, divers breathing it will die.

Could pockets of trapped air persist?

For submarines resting for decades on the deep ocean floor I think you may also need to take into account the solubility of oxygen and nitrogen in water at high pressures.

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If the submarine is sunken, it means it has a solution of continuity in its hull, allowing waters to get in. It can be that, somewhere, pouches of air will be trapped.

Sunken WWII submarine

(source)

Corrosion will happen, however pressure would not be a big deal, since it will be hydrostatic. Also trapped air will be at the same pressure of the water around it.

So, unless the corrosion pierces through the entire thickness of the hull where the air is trapped, it is possible that the air will remain there. However, since the corrosion will have at least weakened the hull, a minimum hit could lead to collapse of the structure.

I would say that cutting through the hull after 50 years will be hazardous, and mechanical attaching point will be no longer usable.

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    $\begingroup$ Thanks, that works fine. I can have part of the ship be damaged enough to have sunk it, but then the rest of the ship was sealed off by the crew to try and contain the breach. When they cut in the ship can start collapsing around them, makes the scene even more dramatic. $\endgroup$ – Ross Coulbeck Aug 27 '18 at 20:10
  • $\begingroup$ “Also trapped air will be at the same pressure of the water around it.” Right, and that means there can only be very little trapped air (volume-wise) because it gets compressed a lot, unless the sub lies at very shallow depth. $\endgroup$ – leftaroundabout Aug 28 '18 at 12:46
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    $\begingroup$ Surface or sub, whenever there is a hazardous situation, all watertight doors are closed and any damage smaller than one compartment can only flood that compartment, and only until the air can no longer get out the same hole. Plus, we were trained in techniques for plugging a hole, often faster than the compartment can fill up. Of course, those techniques can't be used if there are no living persons in the compartment, or if some idiot removed the shoring materials. $\endgroup$ – WGroleau Aug 28 '18 at 18:15
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Depending on how much real world you want a concrete sub could be a solution.

No confirmed real examples exist, but they were rumoured to exist for years. There is an old article here. While it talks about modern (circa 1990) subs it also says

MOD knows about C-subs because they resemble an idea floated by German marine engineer Heinz Lipschutz in 1957

There is what looks like an article about his ideas here (subscription required) but it teases

He even claimed the German Navy built a 7-metre prototype to test his theory

So C-Subs are at least conceivable as part of a cold war era submarine plot.

These subs were designed to sit on the seafloor for long periods and fire up at traditional subs. They may actually have negative buoyancy and only be able to surface by moving forward (and up).

I'd guess that a concrete hull would be less likely to leak and corrode than a metal one so you could easily explain the longevity.

Of course, cutting through a concrete hull would be difficult but a moon pool may be feasible if the sub was designed to sit there for long periods.

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Seawater is quite corrosive. Any bare metal (which will likely be some sort of steel) will be vulnerable, although stainless alloys less so. Yes, it can be painted, and if the paint is good enough, will serve as a barrier against corrosion. But, anywhere you have moving parts like hatches, there is bound to be metal on metal with no paint protection. There should be lubrication - grease - which should offer some protection from the seawater, but it won't likely be an unbroken barrier.

All of this is to say that after 50 years, chances are there will be some places where corrosion has occurred.

The thing about corroding metals is that they take up (usually) oxygen from the environment to form oxides. These new compounds take up more space than the original metal - in other words, metals expand as they corrode. This can cause parts to distort out of shape, and the corroded (expanded) metal ends up exposing fresh metal to further corrode.

So, things like hatches are likely to start corroding (bound to be gaps somewhere), which will cause them to distort, which will probably cause them to start leaking. Fast-forward 50 years, and there is likely little or no hermetic seal left intact anywhere aboard.

Now if your sub sank in fresh water, the situation might be different. Fresh water isn't nearly as corrosive.

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