The 18-hour day is dead and gone in the submarine force, and junior officers who were on the front lines for the change say the change has been a revolution for morale and alertness throughout the force.

The submarine force began transitioning in 2014 from an 18-hour day, where sailors stood watch six hours and had 12 hours off for other duties and sleep. Five junior officers speaking on a panel at the Naval Submarine League's annual symposium all agreed that the change to eight-hour watches with 16 hours off had an immediate positive affect.

"It has had an extraordinary impact on a couple of areas," said Lt. Travis Nicks, who was on a fast-attack boat when his ship switched to eight-on, 16-off watches. "Mission execution and alertness. I did one deployment with six hour watches and one deployment with eight-hour watches. And on the eight hour deployment, nobody fell asleep as the contact manager standing up. The officer of the deck wasn't leaning up against the scope with both eyes closed and being slapped by the junior officer of the deck to stay awake.

"I know that sounds like whining to everyone in this room who went their whole career on six-hour watches but I wish you'd had the experience of eight-hour watches because it's life-changing," Nicks said.

The impact was also immediately apparent for crew morale, he added.

"The second part is it dramatically improves morale on the ship," he said. "When guys are sleeping, I noticed immediately that guys are complaining less. They need fewer bathroom breaks. They're dipping less tobacco. Everything gets better with eight-hour watches."

Experts such as Nita Shattuck, an associate professor at the Naval Postgraduate School, have argued for years that even without sunlight the body works best on a 24-hour clock and that the 18-hour day led to chronic sleep deprivation among sailors which has led to accidents over the years.

In 2013, the heads of the Surface Navy released a statement saying that their force should also make a priority out of sleep.

"The aviation community has long embraced the concept of crew rest as a foundation for safe operations," said Vice Adm. Tom Copeman, then head of Naval Surface Forces, and Rear Adm. David Thomas, then head of Naval Surface Force Atlantic. "It has a place in the surface force, as well."

For Lt. Jessica Wilcox, who served on the ballistic missile sub Wyoming, the benefits of sticking to a 24-hour clock underwater were written on her sailors' faces.

"We implemented them on my last patrol and it was a godsend," she said. "Mostly the way I saw it was in my [engineers] and the bags that they didn't have under their eyes anymore."