Former US Navy Submariner explains why 120 days is the longest time a submarine can remain underwater

Former US Navy Submariner explains why 120 days is the longest time a submarine can remain underwater

By Dario Leone
Feb 17 2023
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‘After 110 days at sea we were left with one canned ham, a crap load of white cake mix and some dehydrated fruits and vegetables,’ Jeffrey Knight, former US Navy submariner.

A submarine is a watercraft capable of independent operation underwater: it operates in an unforgiving, complex and highly pressurised environment.

A submarine submerges by taking in ocean water into large tanks. This weighs it down, allowing it to submerge. A submarine takes in as much as it needs to go as low as it wants to. When it wants to come back up, it pumps out the water by pumping pressurized air into the tanks.

What is the longest time a submarine can remain underwater given the state of technology today?

‘My answer is regarding my experience on US nuclear subs,’ Jeffrey Knight, who is qualified on 4 different classes of US Navy submarines, says on Quora.

‘As I understand it now, most subs’ reactor cores are good for greater than 20 years. That makes the water, electricity, and good breathable air.

‘Crew size can be 110 to 140 plus any special ops types. Food for them can be stowed everywhere you can imagine. It was normal in the ‘70s and ‘80s to walk on cans and cases of food in berthing until we ate enough to take the level down to normal storage.

‘After 110 days at sea we were left with one canned ham, a crap load of white cake mix and some dehydrated fruits and vegetables. I know other boats experience the same.

‘Naval reactors have to be monitored and maintained to keep running. Unlike commercial reactors that are made to run nonstop with limited human intervention, the US Navy reactors are designed to shut down for any number of things if not addressed in a timely manner.

‘That said if the crew ran out of food and started dying off, the reactor and everything else would very soon after, start shutting down.

The boat would lose forward propulsion and depending on trim would very slowly surface or fall to the depths below.’

Knight concludes;

‘So, I would say 120 days max. Or 5 days after the coffee ran out.’

Photo credit: U.S. D.O.D. graphic by Ron Stern

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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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  1. Bob Lemmon says:

    “Sink” is not the same as “submerge.” A submarine submerges when it releases air from its ballast tanks. It sinks when something really bad has happened. This ain’t rocket science; it’s submarine science.

  2. bolo821 says:

    My Qual boat was USS Tullibee SSN-597. I have since served on Sturgeon class, Permit class and all 3 flights of the 688 class. We once pulled into port after being out and all we had was a bag of chili powder and something unrecognizable but it was a meal. I don’t know who wrote some of the stuff in this article but it was…….funny……I would further tho that coffee grounds can be recycled, not too many times, and there are only so many snuffed cigarette butts you can scrape together to make a smoke. There is always food, just in case…….non quals taste like chicken……hahahahahahaha

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