One That has a Relatively Low Emission
It is absolutely necessary for submarines to keep a low profile in order to avoid being spotted by other vessels. Because of this, the hulls of these vessels have an anechoic coating applied to them. The hull of the submarine is covered in intricately crafted rubber tiles that are adhered to the surface of the hull.
The acoustic profile of the vessel has been greatly reduced as a result of the sound-absorbing properties of these rubber tiles. They help to reduce the amount of noise that the submarine makes, which is another way in which they contribute to its ability to maintain as little noise as possible.