The bullet passed through Lance Corporal Juan Valdez- Castillo as his patrol moved down a muddy urban lane. It was a single shot. The marine fell against a wall, tried to stand and fell again. His squad leader, Sergeant Jesse Leach, faced where the shot had come from, raised his rifle and grenade launcher and quickly stepped between the sniper and the bloodied marine. He walked backward, scanning, ready to fire.
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In recent months, military officers and enlisted marines say, the insurgents have been using snipers more frequently and with greater effect, disrupting the military's operations and fueling a climate of frustration and quiet rage.

Throughout Iraq, the threat has become serious enough that in late October the military held an internal conference about it, sharing the experiences of combat troops and discussing tactics to counter it. There has been no ready fix.