As his convoy rode toward Balad, iraq, on a 116-degree day last July, U.S. Army Staff Sergeant Robbie Doughty sat facing out the side of a Humvee, gun in hand, scanning the roadside to head off an ambush. Then: boom, and smoke everywhere. When Doughty looked down, blood was gushing, most of his right leg was gone, and his left leg had taken a dogleg at the shin.