‘To military aircraft pilot’s, “speed is life”. To submariners today, “stealth is life”,’ Dave Corley, former US Navy Submarine officer.

Silent running is a stealth mode of operation for submarines.

During silent running, the propellers have a characteristic RPM band in which no cavitation noise arises. Since this rotation speed is usually relatively low, the first electric submarines had special “silent running” engines designed for optimum performance at reduced speed.

Nuclear submarines can run even more quietly, at very low speeds only, by turning off active reactor cooling during silent running. The reactor is then only cooled by natural convection of the water.

The aim of silent running (a protocol that has been in use since the latter part of World War I, when hydrophones were invented to detect U-boats) is to evade discovery by passive sonar by eliminating superfluous noise: nonessential systems are shut down, as explained above speed is greatly reduced to minimize propeller noise and the crew is urged to rest and refrain from making any unnecessary sound.

‘Being “quiet” is more than not talking,’ Dave Corley, former US Navy Submarine officer (1977–1997), says on Quora.

‘Any submarine CO, XO and Chief of the Boat (COB) worth their salt enforce silent operation as a boat’s policy – regardless of the boat’s nationality. To military aircraft pilot’s, “speed is life”. To submariners today, “stealth is life”. The principle way to relax stealth when at sea on a submarine is to be “not quiet” in any way.’

Corley continues;

‘The CO on my second boat had a habit that he transmitted to his shipmates – when shutting a compartment door (not a watertight door), open the door handle before shutting the door. This removed the “click” sound when the latch hit the door jamb. The intensity of the sound when a door “click” happened was probably not likely to be heard by any other submarine. But the habit overtly reinforced the idea to crewmembers to consciously think about their actions with respect to making noise throughout the day at sea.

‘On that boat, that door-shutting was so much ingrained in the habits of my shipmates that we continued doing it even in overhaul.’

Corley concludes;

‘It’s easy to make specific rules – “During ‘Rig for ultra-quiet’, don’t flush the TDU”, but it’s even better to make a simple habit that reinforces a life-preserving goal.’

Photo credit: U.S. Navy photo by Mass Communication Specialist 1st Class Hana’lei Shimana