The U.S. military has a new secret weapon: napping. In October, the Army released updated guidelines for soldiers, recommending “short, infrequent naps to restore wakefulness and promote performance.” The advice is part of an overhaul of the Army’s training manual, which puts a new emphasis on mental health in addition to grueling physical challenges. And officials believe encouraging more rest is key, as sleep deprivation during missions can cripple decision-making and lead to disaster. Other branches of the military have taken similar steps; the Navy recently updated sleep schedules at sea after determining that fatigue was a factor in two fatal collisions. Army officials hope the new guidelines will help bust the myth that tough people never rest. “Combat is a thinking man’s business,” says retired Lt. Gen. David Barno, commander of combined forces in Afghanistan from 2003 to 2005, “and your brain doesn’t function without sleep.”