I was visiting the Museum of Science and Industry in Chicago (highly recommended) and I took the tour of the complete U-Boat (U-505) that they have housed there. It's extremely well-preserved inside and quite fascinating. However, the guide was not able to shed any light on the quite spectacular number of valves poking out literally everywhere. I'd love to get a sense of their purpose and also how on earth anyone would know which to turn and when. I've attached a photo of one such group, and there were many more peppered throughout the entire craft.

enter image description here

Also how did the crew train to be able to operate all this, and how did they communicate which valve to adjust. It would not be a case of "turn the red and black one!"

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    $\begingroup$ Do you have higher resolution and/or other angles? There are labels visible. $\endgroup$
    – Chris H
    Mar 29, 2023 at 14:02
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    $\begingroup$ The museum is The Museum of Science and Industry and the submarine is the U-505 $\endgroup$
    – Theodore
    Mar 29, 2023 at 18:57
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    $\begingroup$ No other photos sorry - we had a group behind us and I was lagging already. And yes I got the museum name wrong. Fixed. $\endgroup$
    – Tim Smith
    Mar 29, 2023 at 23:52
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    $\begingroup$ I can't find a photo, but at the Australian Maritime Museum (which has a post war Oberon class diesel boat on display) there is a display of valves, showing that different systems used different shapes of hand wheel, so that you could identify them by touch. $\endgroup$
    – tgdavies
    Mar 31, 2023 at 2:42
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    $\begingroup$ @tgdavies this set has some on backwards compared to the others. That would be easy to feel, and enough to provide a datum from which to count. There could conceivably be some relationship between the shape and which you'd turn (which way) in the direst emergency. $\endgroup$
    – Chris H
    Mar 31, 2023 at 6:55

6 Answers 6


I don't know what that specific stack was for. You could have traced one of the lines and probably figured it out. Like do they lead to an air blower or diesel generator or hydraulic accumulator or what.

On modern US submarines the valves are all labeled by system and number. E.g. MS-1 (main steam one). Usually that would be engraved into the hand wheel or lever or what have you. So, no, not "the red one". They have procedures and numbers and a disciplined way of operating with orders and repeat backs and the like when starting up a system or shutting it down or reconfiguring it. (The valves also have non-operational modes to be used to isolate leaks in a casualty or to allow repairs.)

There are a lot of fluid systems. Control air, hydraulic fluid, lube oil, sea water, bilge water, diesel oil, ventilation, fresh water, etc. Nuke submarines will have more different fluids than a diesel boat because you have piping associated with the nuke (primary piping) as well as with the steam plant (secondary piping), and more auxiliary systems like atmosphere equipment and air conditioning, along with all the aforementioned systems (even the diesel generator) that the diesel boat had.

P.S. I recommend to stream and watch the movie Run Silent, Run Deep for a view of diesel boat operations. You won't see that specific valve tree, but will see how the crew operates. It was filmed on an actual US fleet boat. It's got some Hollywood human interest mixed in, but the orders and repeat backs seemed very authentic, as well as seeing hatches dogged and ventilation isolated when rigging for depth charge. The "style" is not much different from how US nuke submarines operate, even now. (Or at least when I was in.)

P.P.S. "Valves sticking out all over the place" is normal on a submarine. There's a lot less room and all/more fluid systems than you'd have in a surface combatant. I remember tall guys would curse when they hit one or even just grazed one and it cut their scalps.

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    $\begingroup$ And the submariners even know them in the dark, since you don't know if the lights will work and can't guarantee there isn't smoke in the compartment... $\endgroup$
    – Jon Custer
    Mar 29, 2023 at 12:49
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    $\begingroup$ This is a good answer thank you, and the extra detail (and movie recommendation) is much appreciated $\endgroup$
    – Tim Smith
    Mar 29, 2023 at 14:24
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    $\begingroup$ 1. I quite like the answer by Chris H (looks like best one). 2. There is an interesting diaphragm or disc or something in your photo (below the L shaped red valve), sort of right/up from center of picture. Can't remember what that is, but it might be a clue to the fluid...like is that an air thing? $\endgroup$
    – guest
    Mar 29, 2023 at 15:04
  • $\begingroup$ These ones are labelled. I read "Hd Luft*****" on the left (Luft=Air) and "Hd Flaschange" on the right (not sure) and there's another vertical thing that might say "Druck Hd / Druck Luftart" (press for Hd / press for air type???) $\endgroup$
    – user253751
    Mar 30, 2023 at 6:58
  • $\begingroup$ Like fighter pilots, submarine crew is another job in the military where it really helps to be a bit shorter than average for this reason. $\endgroup$ Mar 31, 2023 at 14:31

In the left column I'm fairly sure I can pick out words beginning "Luft" ("air") a couple of times, with "Hd" before it (probably meaning "Hochdruck", so "high pressure"). If the adjacent gauges show pressure in Bar, that certainly is high pressure, roughly the pressure in a cylinder of air or nitrogen, and the pipework looks beefy enough for that.

That's all I can say with reasonable certainty, so this is speculation. What, on a submarine, might use high pressure air with multiple related systems, and the need for pretty high flows (judging by the diameters of the pipes). My guess would be to blow the ballast tanks. Certainly that's a system that would have multiple valves per tank (air in and water in as a minimum, apparently they were open outlet on that model), and multiple tanks (for trim). So even if I'm wrong in this case that's an example of a system that would require a bank of valves. Some are likely to be remote actuators in that case - perhaps some of the smaller handwheels and pipes control remote valves.

U505, preserved in Chicago, is a type IXC. While I can find a lot of information (naval-encyclopedia.com) I can't easily find a really good cross-section or a description of the ballast system. However u-boat.net has some interesting internal photos, including a shot of this same bank of controls, described as compressed air valves. Such valves were also used for launching torpedoes, which explains why there were quite so many.

  • $\begingroup$ No I had the same problem. Some nice resources out there but not really in-depth enough. Feels like one may have to go to some old archive and scour blueprints $\endgroup$
    – Tim Smith
    Mar 29, 2023 at 14:23
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    $\begingroup$ @TimSmith I've found some more photos online, low res scans of prints, but with helpful captions, and it looks like I was pretty much right with my guess. Edit coming $\endgroup$
    – Chris H
    Mar 29, 2023 at 14:44
  • $\begingroup$ clever old stick you are :D $\endgroup$
    – Tim Smith
    Mar 31, 2023 at 3:07

They are all labeled.

On a submarine you learn what all the valves do. Qualification involves drawing every system including labeling the valves. I still remember what MS-1 to 5 were.

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    $\begingroup$ Well, anybody could have guessed that much, couldn't they? The question was, what is the valves' purpose! It should be possible to answer that at least to some extend in a rough, high-level way, no? $\endgroup$ Mar 29, 2023 at 11:14
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    $\begingroup$ Congrats, you managed to get a "Nice Answer" badge for simply writing RTFM. $\endgroup$ Mar 30, 2023 at 8:02
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    $\begingroup$ @EricDuminil this answers the question in the body (if not the title) "how on earth anyone would know which to turn and when" $\endgroup$
    – stannius
    Mar 31, 2023 at 14:04

What do all those different valves do? I'll try to keep my answer short.

First of all, there are a large number of tanks both inside the pressure hull and outside the pressure hull of a sub that can contain high pressure air, ambient pressure air, sea water, fresh water, fuel oil, lubricating oil, etc. Those tanks feed pipes that run throughout the sub and through its pressure hull and all those valves are used to convey the tank contents via pipes to wherever they are needed.

For example, one set of tanks, pipes and valves are used to move sea water back and forth along the length of the sub and from side to side inside the sub, in order to get it to float level when submerged and when on the surface.

Another set of tanks, pipes and valves are used to get the sub to float on the surface at the proper height above the water level, regardless of how much the sub weighs.

Yet another set of tanks, pipes and valves is used to set the weight of the sub so that when it must suddenly submerge, it will be neutrally bouyant (as close to that as possible) when the air keeping it afloat is released.

Another set of tanks, pipes and valves is used to blow air into the flotation tanks to bring the sub back to the surface after a dive.

In the engine room, there will be valves in the intake pipes feeding outside air to the diesel engines and valves in the exhaust pipes carrying exhaust out of the engines and out of the sub's hull. There will also be valves to conduct cooling water from outside the hull to the engine blocks and valves to feed fuel oil to the engines from a variety of different oil storage tanks in the sub.

Note also that the sub has a complete fresh water plumbing network to furnish water for washing, cooking and drinking from the distillation machinery to all the different compartments in the sub- and a sewage system to carry away all the waste water as well. This means still more pipes with valves in them.

It is also common for a single pipe to have several valves in it so if one valve fails or a portion of the pipe blows up and starts to leak, there will be some other means available to shut off the pipe and save the sub from sinking.


FWIW, U-505 is a type IXC boat. There is a German memorial of U995, type VIIC, which was much more common and somewhat smaller.

Pictures of U995 are availiable e.g. at http://www.u-995.com/galerie.html. In particular, your stack of wheels, labelled with "Luft" and more, look similar to the "Tannenbaum" (Christmas tree) shown on http://www.u-995.com/zentrale.html (middle of the page), which indicated that those wheels operated the valves responsible for blowing the water out of the diving (buoyancy) tanks. I'd guess that red/green colours would indicate port/starboard side tanks.


Came across your question. I study VIIC and IXC systems in detail in my free time and figured I'd help! Please see attached (based on the IXC Skizzenbuch, Band M).

The first image is for the high-pressure air manifold (the longer one to the left). The second is for the low-pressure air manifold (shorter one below and to the right).

The pressure reducer I've indicated is at this point a mystery. The regulating bunkers would carry fuel at patrol start and were compensated (meaning the fuel was delivered from them) by low-pressure air (the remaining fuel bunkers and fuel ballast bunkers were compensated using water pressure). I think this pressure reducer is to drop the pressure from the 12 atm provided by the LP air manifold down to the 0.5 atm required for fuel delivery from the regulating bunkers. But more to be seen on that once I can make it back down for a closer look. It's tricky as some IXs had it, some didn't, and I don't have a sketchbook plan with it (presumably those that didn't used the normal blowing manifold for regulating tanks/bunkers and would've needed to be gingerly with it to keep it at 0.5!).

At some point I'd like to give detailed technical tours of U-505. I could fill hours, and I'm out of Milwaukee. Just a question whether the museum would want to allow it, but I think they could make a premium on them.

In terms of the valve coloring, it has to do with what the valve should be when the boat is "dive-ready". Green should mean open in a "dive-ready" condition, red should mean closed. The museum didn't get them all right, but many it did.

HP Air Manifold

LP Air Manifold

  • $\begingroup$ This is a nice answer and I really appreciated the labelling $\endgroup$
    – Tim Smith
    Oct 28, 2023 at 16:09

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