Most missions were not lethal. Several Team 6 members said they herded women and children together and knocked men out of the way, with a push or a gun muzzle, to search homes. They frequently took prisoners; a number of detainees had broken noses after SEALs punched them in struggles to subdue them, one officer said.

The Team 6 members often operate under the watchful eyes of their commanders — officers at overseas operations centers and at Dam Neck can routinely view live surveillance feeds of raids provided by drones high above — but are also given wide latitude. While Special Operations troops functioned under the same rules of engagement as other military personnel in Afghanistan, Team 6 members routinely performed their missions at night, making life-or-death decisions in dark rooms with few witnesses and beyond the view of a camera.

Operators would use weapons with suppressors to quietly kill enemies as they slept, an act that they defend as no different from dropping a bomb on an enemy barracks. “I snuck into people’s houses while they were sleeping,” Mr. Bissonnette says in his book “No Hero,” written under the pseudonym Mark Owen. “If I caught them with a gun, I killed them, just like all the guys in the command.”

And their decisions tend to be certain. Noting that they shoot to kill, a former noncommissioned officer added that the operators fire “security rounds” into those who are down to ensure that they are dead. (In a 2011 mission on a hijacked yacht off the coast of Africa, one Team 6 member slashed a pirate with a knife and left 91 wounds, according to a medical examiner, after the man and other attackers killed four American hostages. Operators are trained “to slice and dice every major artery,” said one former SEAL.)

The rules boiled down to this, the noncommissioned officer said: “If in your assessment you feel threatened, in a split second, then you’re going to kill somebody.” He described how one SEAL sniper killed three unarmed people, including a small girl, in separate episodes in Afghanistan and told his superiors that he felt they had posed a threat. Legally, that was sufficient. “But that doesn’t fly” in Team 6, the noncommissioned officer said. “You actually have to be threatened.” He added that the sniper was forced out of Team 6.

A half-dozen former officers and enlisted troops who were interviewed said they knew of civilian deaths caused by Team 6. Mr. Slabinski, a former senior enlisted member of SEAL Team 6, said he witnessed Team 6 members mistakenly kill civilians “probably four or five times” during his deployments.