KORANGAL OUTPOST, Afghanistan — Only the lead insurgents were disciplined as they walked along the ridge. They moved carefully, with weapons ready and at least five yards between each man, the soldiers who surprised them said.

Behind them, a knot of Taliban fighters walked in a denser group, some with rifles slung on their shoulders — “pretty much exactly the way we tell soldiers not to do it,” said Specialist Robert Soto, the radio operator for the American patrol.

If these insurgents came close enough, the soldiers knew, the patrol could kill them in a batch.

Fight by fight, the infantryman’s war in Afghanistan is often waged on the Taliban’s terms. Insurgents ambush convoys and patrols from high ridges or long ranges and slip away as the Americans, weighed down by equipment, return fire and call for air and artillery support. Last week a patrol from the First Infantry Division reversed the routine.

An American platoon surprised an armed Taliban column on a forested ridgeline at night, and killed at least 13 insurgents, and perhaps many more, with rifles, machine guns, Claymore mines, hand grenades and a knife.