May 1945, Okinawa. Sledge, Leyden, Snafu, and Burgin toil through the mud with new arrivals Hamm and Kathy, and for the first time in the war, they encounter civilians. The thunder of artillery is constant in the muddy wasteland of ridges and draws, where corpses decompose in the muck. The men are horrified by the Japanese use of civilian women and children as shields in combat. Leyden is wounded and taken off the line. When Hamm is killed, Sledge and the others are driven perilously close to the edge.
Sledge and the Marines continue their advance and systematically clear out the entrenched Japanese. In a hut, Snafu and Sledge find a crying baby at his slain mother's breast. A mortally wounded old woman begs Sledge to shoot her and end her misery. Once again at a moral crossroads, Sledge instead cradles her in his arms as she dies. He later spares the life of a Japanese boy soldier, only to see him shot and killed by a newly-arrived Marine. The battle won, Okinawa secured, Sledge, Snafu, Burgin and the rest of their unit are informed by Lt. Mac that the Americans have dropped some kind of new bomb that has vaporised a Japanese city. But the war isn't over.