After nearly a decade of research the U.S. Navy has concluded that a half century old practice adopted to keep sailors on nuclear submarines alert while minding the nuclear reactors was in error. Back in the 1960s the navy noted that sailors monitoring nuclear reactors on subs got tired towards the end of their eight hour shift. So the navy adopted an 18 hour work day, with sailors only required to monitor the reactors six hours per shift. But still the sailors eventually got tired. Since 2005 the navy has been conducting research to find out why. Turns out that sailors working a schedule that was out of sync with the 24 hour day was in itself a source of fatigue. That was because the circadian rhythm (sleep on a regular schedule in order to be most alert and healthy) for humans is based on a 24 hour day and there is no practical way to change that. The navy researchers also noted commercial firms had found that workers who changed shifts a lot also suffered from reduced alertness, productivity and morale. That’s all because the circadian rhythm cannot be fooled. The circadian rhythm is most efficient when people sleep at night, but you can work night regularly with some decrease in effectiveness if you stick with the night shift for a long time. The greatest losses in alertness and efficiency come when you constantly change the time you can sleep. Thus the navy’s traditional work schedule was the most inefficient available.
The navy has tested a new submarine work schedule what respects the circadian rhythm and has found (via sensors sailors wore during testing) that alertness was much improved and opinion surveys found morale was much higher as well. Sailors tending the reactors still got tired towards the end of their shift, but not to the extent they experienced while living and working with an 18 hour “day.” The navy now has the submarine crews on a 24 hour day, always working the same shift and thus sleeping on a regular schedule. The new schedule is much appreciated because it doesn’t fight the circadian rhythm and the sailors quickly felt the beneficial impact of that.