Might sleep impacts in diesel-electric submarines be different from those impacting nuclear submariners? Might a sleep deprived SSBN Trident D5 nuclear weapons officer (above) pull the big red buttoned trigger in error? Will nuclear defenders everywhere exude the inner glow of the long gone (free fall nuclear bomb) B52 spelling the end of personkind? These, and other questions are untouchable in the following overt tip of a largely classified iceberg, as we don't know it. 

Will Harris, a third-year medical student at Harvard Medical School, has penned an article of May 14, 2024 for Sleep Review magazine. Before medical school, Will Harris served as a nuclear submarine officer in the United States Navy for eight years. The article is at https://sleepreviewmag.com/sleep-health/demographics/career/submarine-deployment-sleep-quality/ :

"How Submarine Deployment Impacts Sleep Quality
of May 14, 2024

As a medical student interested in providing better advice on sleep habits to my patients, I recently started reading the book Why We Sleep by Matthew Walker. In its first chapter, the book describes the Mammoth Cave sleep experiment, in which two researchers lived underground for 32 days with a constant ambient temperature and no exposure to natural light. 

Living in a cave for more than a month might seem like a radical idea, but to me, it feels familiar. Thirty-two days in a confined space with constant ambient temperature and no exposure to natural light seems like a fairly short period, actually. I’ve lived in such an environment for well over 100 consecutive days. And thousands of people are living like this right now onboard nuclear-powered submarines.

Life on a Submarine

Before starting physician training at Harvard Medical School, I was a submarine officer in the United States Navy. I spent three years on board a nuclear-powered fast-attack submarine based in Bangor, Washington. During this time, I spent about one year underwater. 

Life on board a submarine can be challenging for many reasons.

• You might see the sun through the periscope occasionally if you’re lucky. There is no other exposure to natural light. 
• Submarine crews do not always follow a 24-hour day. An 18-hour day is common, in which sailors are typically awake and working for about 12 hours and asleep for about six hours.
• The diet consists of canned fruits and vegetables (fresh produce runs out after about a week), powdered milk, frozen meat and fish, and baked goods. 
• In terms of exercise, a crew of about 150 sailors can share one exercise bike, some free weights, and one or two treadmills (depending on the submarine’s size).

Since all American submarines are equipped with nuclear reactors, they have the fuel to stay at sea for decades. They also can create oxygen and water. So time at sea is limited only by the amount of food carried on board.

Since leaving the submarine force and starting medical school in 2021, I’ve thought a lot about the physiological impacts of a submarine deployment. Here is what I’ve learned about how an 18-hour day on a submarine deployment can affect cognition and sleep quality. 

Three Studies on Submarines and Sleep

Researchers have tested the effects of circadian rhythm and sleep-wake patterns on cognition and sleep quality using a protocol called forced desynchronization, under which participants follow a consistent sleep-wake cycle that is different from 24 hours.

A 1999 study used submariners following an 18-hour-day schedule as test subjects for studying circadian rhythm. The submariners followed a typical work-sleep schedule of 12 hours working and six hours sleeping during a three-month patrol. Saliva samples were taken periodically to measure melatonin levels. This study found that the circadian period of test subjects remained around 24 hours.

We can feel confident that submariners’ circadian rhythm continues to follow roughly a 24-hour schedule, even if they do not. But how does the 18-hour day affect cognition and sleep quality? 

Here, it’s helpful to look at a study in which researchers examined neurobehavioral function and cognition in humans living in a 20-hour day. Test subjects were scheduled for 15 to 24 cycles of a 20-hour rest/activity cycle. Data was collected on circadian parameters such as melatonin and core body temperature, cognitive tests including short-term memory and reaction time, and sleep was assessed using an electroencephalogram. They found that sleep performance and cognition suffered when the circadian rhythm was out of phase with the sleep-wake cycle.

One final study to consider: In 2015, researchers looked at sleep quality for submariners on a 24-hour schedule. Crewmembers underwent polysomnography (PSG) at the beginning of a submarine deployment and on day 51. They also completed surveys on subjective sleep quality. This study found that sleep quality did not suffer based on PSG evaluation or survey data.

Desynchronization Impacts Sleep Quality

In summary, life onboard a submarine presents many challenges, including an 18-hour sleep-wake cycle, lack of natural light, lack of fresh fruits and vegetables, access to exercise equipment, and potential exposures.

Several studies show that sleep-wake cycles and circadian rhythms become desynchronized during an 18-hour day, and such desynchronization can negatively impact sleep quality and cognition. There is evidence that submariners on a 24-hour day do not have their sleep negatively impacted, which suggests that poor sleep is due to an 18-hour day rather than other exposures onboard a submarine, such as the lack of natural light."