While deployed for six months, the crew of the recently returned USS Providence was on a 24-hour schedule, meaning sailors, generally speaking, stood watch and were able to go to bed at the same time every day, a stark contrast from submarine deployments in the past.

The submarine force, as a whole, began transitioning to the new watch schedule, which applies to submarine crews underway, in the spring under the direction of Vice Adm. Michael Connor, then commander of Submarine Force Atlantic.

Connor's decision to make the transition was based on research done by the Naval Submarine Medical Research Laboratory in Groton comparing 18-hour watch-standing schedules with a 24-hour based schedule.

The idea is to get sailors to conform to circadian rhythms, often referred to as the body clock, which follows a 24-hour cycle, ensuring a more vigilant watch and better health for the sailor.

Previously, crews were on an 18-hour schedule while underway, which meant they were on watch for six hours a day and off for 12 hours. Under the new schedule, they are on watch for eight hours and have 16 hours between watches.

Prior to deploying, the crew of the Providence tried out varying scenarios but settled on three 8-hour watch shifts, Cmdr. Tony Grayson, the boat's commanding officer, said by email. The decision was based on crew feedback.

Also based on their feedback, Grayson said, watch times were during the same time period every day. Other boats have opted to shift set watch times every three to four weeks.

"This had two positive effects: it minimized the 'jet lag' that was experienced when shifting to a new cycle. Also, we found that Sailors who are on watch at the same time every day were better able to deal with frequent situations that would occur each day on deployment," Grayson said in his email.

With the increased time between watches, sailors had more free time to take care of their professional duties, read a book or watch a movie, Grayson said.

"We also saw a significant increase in the amount of physical training they began to do as well," he added. "All of this went into greatly improving their mental health."

Whereas on the 18-hour schedule, a sailor could end up going to sleep at midnight one day, and 6 a.m. the next, on the new schedules sailors on the Providence were able to go to bed at the same time every day "to ensure the crew was able to establish and keep their circadian rhythm," Grayson said.

"Imagine how you feel when you fly on a long flight through several times zones. This 'jet lag' is what we were asking our Sailors to deal with everyday by shifting their sleep 6 time zones to the east with each watch," Grayson said. "That schedule affected the Sailors because they would often end up being wide awake when it was time to sleep."

Certain exceptions can arise, in which case commanding officers can call for a temporary watch rotation for a set period of time. An example would be an all-hands drill during a specific time frame.

"To make this schedule work, we also had to shift the mindset of the crew by placing a high priority on protecting sleep periods," Grayson said. "We taught the crew that there were consequences to racking out an individual during their down-time. My supervisors did a superb job with thinking ahead and minimizing the need to do so by not only shifting maintenance and training periods, but by re-thinking which routine notifications and reports actually require interrupting their sleep."

The biggest concern with the eight-hour watches, Grayson said, was the "likelihood for fatigue and hunger."

Initially, to address this, those standing watch would take a break around the halfway point. But the crew expressed their preference for working out their break on their own.

"By leaving it up to each individual, they stood a more alert watch because when they began to feel the (effects) of fatigue or hunger, they immediately were able to get their break," Grayson said. "Furthermore, I found that it was better not to have the whole watchteam relieved at the same time to maintain their focus."

Leadership on the boat also began rotating meals every two weeks after realizing the fixed eight-hour schedule meant the watch teams would be stuck eating the same meals every day.

The first submarine to test eight-hour watches throughout a 24-hour day was the USS Scranton in 2013-14. The Navy decided to allow 24-hour watch schedules for submarines in 2012.

Grayson said his crew "really liked" the shift in schedule. The crew reported having a better quality of sleep, less disorientation with the time of day, and more uninterrupted time to accomplish duties, among other benefits.

Their performance also improved, he said.