The Killer Angels by Michael Shaara

Just before dawn Buford rode down the line himself, waking them up, all the boyish faces. Then he climbed the ladder into the white cupola and sat listening to the rain, watching the light come. The air was cool and wet and delicious to breathe: a slow, fine, soaking rain, a farmer's rain, gentle on the roof. The light came slowly: there were great trees out in the mist. Then the guns began.

A single shot. He sat up. Another. Two more widely spaced. Then a small volley, a spattering. A long silence: several seconds. He stared at white air, the rounded tops of smoky trees. Men were moving out in the open below him.