You want your submarines to be really hard to detect. For the ones carrying the nuclear missiles, staying hidden is absolutely critical - it's not hard to destroy a submarine you know the position of.
There are two basic ways to find a submerged submarine. You can search for it 'actively', for example doing sonar pings, but that gives away where you are. (As with using a torch to find someone, they can hear the pings from much greater distances than you can find them with it.) Or you can search 'passively' and the classic way to do that is to listen for it, taking advantage of the way that sound travels further and quicker in water than it does in air.
So you want quiet submarines. One of the big problems is the noise the propellers generate. As the blades spin round, the rapidly changing pressure in the water causes bubbles to form - it's called cavitation - and reducing this is a critical aim of propeller design, because they are then crushed by the water pressure, especially at depth, and this can be heard for quite a distance.
![[community profile]](https://www.dreamwidth.org/img/silk/identity/community.png){kind=small}
![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
timeasmymeasure
Submarines and propellers - why this is important in real life
Date: 2014-03-13 01:20 pm (UTC)There are two basic ways to find a submerged submarine. You can search for it 'actively', for example doing sonar pings, but that gives away where you are. (As with using a torch to find someone, they can hear the pings from much greater distances than you can find them with it.) Or you can search 'passively' and the classic way to do that is to listen for it, taking advantage of the way that sound travels further and quicker in water than it does in air.
So you want quiet submarines. One of the big problems is the noise the propellers generate. As the blades spin round, the rapidly changing pressure in the water causes bubbles to form - it's called cavitation - and reducing this is a critical aim of propeller design, because they are then crushed by the water pressure, especially at depth, and this can be heard for quite a distance.
Partly because Soviet subs were significantly noisier when moving, there was a major intercontinental system set up to listen for them, and the Soviets really wanted to make them quieter...
... so this is a big thing that they're after.