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Regardless which films and also reports I'm looking at, it is indicated that too loud sounds from inside a submarine could tip an enemy destroyer off to its whereabouts.

What intrigued me there the whole time is if it was thought about and what was the reason against just soundproofing the interior of submarines? (you can do it with rooms so not sure what stops one from doing the same for submarines there).

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    I mean, sundproofing doesn't stop 100% of all sounds on land either. – Semaphore May 6 at 20:48
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    Sound proofing tends to be bulky and submarines are very space-constrained. – Gort the Robot May 6 at 21:16
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    Sound-proofing the hull would have been a nice luxury in the 1940s but they had no way of sound- proofing the cavitation created by the propellers, and that was the major sound heard by sonar. It would have been a waste of money. – Carey Gregory May 7 at 1:25
  • @CareyGregory it always sounded like when they KNEW they were spotted they would turn off the propellors but had troubles as the IN sub sounds were too loud still (crew and machines inside the sub) – Thomas May 7 at 11:00
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While a staple of entertainment, single transient noises from the crew are not that significant in locating a submarine as there are many sources of biological noise in the ocean.

Far more significant are rhythmic/cyclic noises from machinery that are both 'louder' and have patterns that make them easier to pick out.

Therefore Submarines are 'sound proofed' but the effort happens in the machinery spaces in ways that do not show up well on film in the form of careful design work in balancing rotating plant, absorbent mountings and avoiding cavitation/flow noise both outside (propellers) and inside(pumps and pipework) the hull.

All of this effort only helps if the search is being done passively. If the searching party is pinging with active sonar the way the hull reflects the acoustic energy of the ping matters far more than the noise coming from inside the hull or lack thereof.

This is why the 'turn everything off' ploy mentioned in a comment only works if the submarine has not already given away enough location information to trigger an active sweep of that specific patch of ocean,

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  • Including special grade ball bearings tested for sound generation. – blacksmith37 May 7 at 15:38
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Why were submarines not made sound proof?

They were and are

We have to remember that the term soundproof suggests an unreachable ideal terrestrially. All real-world soundproofing systems are only partially effective. You can reduce sound but you can never completely eliminate it in practise (outside a laboratory).

Sound reduction has a cost. It may be better to have ten quiet submarines than one very quiet submarine. Particularly if the quiet submarines have better speed, better range, more and better armaments then the very quiet submarine.

Water is a great transmission medium for sound. Sound travels faster in water than in air. Whale song can be heard 80-160 km (50-100 miles).

Traditional submarines are intrinsically noisy. They are generally constructed almost entirely of metals and contain a great amount of machinery and metal objects and tools. Of necessity a lot of the internal metalwork and machinery (plumbing, propulsion, controls, periscopes, hatches) is connected to metal surfaces that are in contact with exterior water. This is also true of the structural elements - floors, walkways and so on.

Space is often at a premium. Soundproofing materials and measures often consume significant space.

All these aspects make creating a soundproof submarine a challenge.

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