US Navy Submariner explains why Submarines can’t flush the toilet while operating in hostile waters

US Navy Submariner explains why Submarines can’t flush the toilet while operating in hostile waters

By Dario Leone
Nov 18 2023
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Submarines toilet

Just like surface ships, the toilet on board a submarine is referred to as its head out of traditional maritime custom.

According to, compared to their surface cousins, submarines have a much more difficult time dealing with mundane operations including flushing the toilet.

Blowing Sanitaries

A claim confirmed by Dale Rich, former US Navy submariner, on Quora.

Rich explains;

‘Submarines have sanitary tanks that are designed to hold the human waste generated in the heads (shipboard bathrooms in the Navy). These tanks are routinely flushed to the open sea when the boat is in normal operating condition and is usually done when the boat is close to the surface while making routine evolutions at periscope depth. These tanks are emptied by using air stored in the air banks to pressurize the tanks to a pressure that is above the sea pressure exerted on the boat at the depth where the boat is operating. An example would be that if the boat was at 100 feet depth at the keel, the air pressure to remove the waste would have to be above 44psi. This routine procedure is called “Blowing Sanitaries” and is performed by the Machinist gang on the boat.’

Operating in hostile waters

Rich continues;

‘When a submarine is operating in hostile waters, is on a mission to trail an enemy combatant, or is operating at extreme depths, the sanitaries cannot be emptied. There are various reasons for this but the primary reason is that the evolution has the potential to make significant noise and uses vital resources to perform the evolution. If the boat is at extreme depth (below 500 feet) the amount of air needed to remove the waste increases dramatically. (at 500 feet at the keel it would require air pressure to be above 215psi to push the waste from the tank) Air is a vital commodity on a submarine, and might be needed, and better used, to push the submarine to the surface in an emergency rather than being wasted pushing waste out of the sanitary tank.’

Mercy Blow

‘It is not unusual for a submarine to remain in a position where it cannot expose itself for many days at a time. During this time the sanitaries start to fill up, and the heads are restricted. No showers, no laundry, limited use of the head, no extra use of water. Usually this is when the crew begins to beg for a “Mercy Blow.” The officer of the deck is always apprised of the situation and informs the Captain of the problem. Measures are taken to alleviate the situation if possible.

Rich concludes;

‘This is just one more problem that submariners have to deal with, but remember, all of them are volunteers and do the job because they love it!’

US Navy Submariner explains why Submarines can’t flush the toilet while operating in hostile waters
USS Will Rogers (SSBN-659, a US Navy Benjamin-Franklin-class ballistic missile submarine in service from April 1967 through November 1992) at the National Museum of the US Navy.

Photo credit: SmarterEveryDay YouTube channel and National Museum of the US Navy

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Dario Leone

Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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