[...] Boyd had been at his post since 2 in the morning. At 10:30 a.m., he noticed the muzzle of an AK-47 rifle protruding from the driver’s window of a private vehicle that approached him and the [unarmed Qatari] guard outside the checkpoint. The 6-foot-6-inch Boyd immediately ducked behind a concrete barrier and drew his M-9 pistol.

The driver began shooting, and Boyd had returned fire when the man left the car and ran toward the Qatari guard. The guard knelt on the ground, with hands over his head, while the attacker shouted in Arabic and held him briefly at gunpoint. The guard then ran off, unharmed.

Boyd said he stopped firing at that point, because he didn’t want to hit the guard.

“The rules of engagement — I didn’t know if he was done firing and he wanted to go,” Boyd said.

But the assailant wasn’t finished: He began moving out from behind the gate shack toward Boyd, all the while firing.

He was “15 feet and closing” from Boyd before he was felled. Boyd unloaded an entire 15-round magazine from his handgun, shooting his attacker six times. The gunman, meanwhile, had reloaded his semiautomatic rifle with a second 30-round magazine during the firefight.

“It would have been better to have an M-16 out there,” Boyd said. A U.S.-Qatar agreement prohibits military members from carrying rifles off base.

“The rounds that we were using, it took six to get him down on the ground,” Boyd said. “I was getting scared. I thought, ‘I don’t know, I’ve only got 30 rounds.’ I just went through a magazine. Finally, he dropped.” [...]