The Associated Press reports on a new Navy submarine sleep schedule that corresponds to natural circadian rhythms.

With no sunlight to set day apart from night on a submarine, the U.S. Navy for decades has staggered sailors’ working hours on schedules with little resemblance to life above the ocean’s surface.

Research by a Navy laboratory in Groton is now leading to changes for the undersea fleet. Military scientists concluded submarine sailors, who traditionally begin a new workday every 18 hours, show less fatigue on a 24-hour schedule, and the Navy has endorsed the findings for any skippers who want to make the switch.