Shortly after the declaration of war between the United States and Korea, mechanical engineering college student Andy Smith inadvertently volunteers for enlistment in the Army while trying to impress his girl friend, Peggy Cole. Peggy is duly impressed and she and Andy are married just before he ships out. During the basic training period, Andy makes several friends in camp, including the melancholy Milo Pagano, who misses his wife and their new twin babies. Upon arriving in Korea, the recruits are placed under the command of fatherly Sergeant Mike Kirby, who dubs them the Peachfuzz Brigade because of their extreme youth. Although the men are green, Kirby takes them on a raid based on information gleaned from a captured Korean soldier, but the squad is ambushed. Overcome with rage when frightened fellow soldier Jinx Hamilton is killed in the attack, Andy recklessly leaps on a nearby abandoned tractor-plow and drives it into the enemy machine-gun nest. Praised for his heroism later, Andy is nevertheless deeply affected by the brutality of combat and, along with Milo, contemplates the futility of war. A few nights later, Andy is on guard duty with Powers, another raw recruit, who is suffering from a bad head cold. When Andy leaves his foxhole to offer Powers some cold medicine, Korean snipers attack the camp, allowing the Korean informant prisoner to escape. Soldier Sollie Kaplan is injured in the assault, and Andy is severely reprimanded for leaving his post and is shunned by the others. Kirby consoles Andy, agreeing that the war is confusing and stressful, but that, despite being a family man, he felt that he had to volunteer to support his country. Gradually, the recruits become hardened with daily fighting and the Peachfuzz Brigade remains intact. Upon arriving in a small village, Lieutenant Lewis summons Kirby with orders to dynamite an enemy ammunition dump. Kirby orders Andy, Milo and Stan Howser to accompany him on the dangerous mission. After successfully blowing up the dump, the men flee, chased by enemy soldiers. Surrounded near a river, the men spot a construction site and realize that the Koreans are building an underwater bridge to bring in heavy tanks. Kirby orders Milo and Howser to report the discovery at camp while he and Andy divert the approaching enemy troops. Kirby and Andy are captured, but Milo and Howser hide in the jungle until nightfall, then they make their way safely back to camp. Kirby despairs that Milo and Howser must have been killed, until an American Air Force attack destroys the construction site and kills the guard, allowing him and Andy to escape. A few days later, a recovered Sollie returns, and Lewis tells Andy that he has been transferred. When Andy learns that a train carrying wounded G.I.s has broken down nearby, he pleads with Lewis to allow him to stay, as he knows he is the only one that can repair the train's engine. Lewis suggests that if Andy were to board the wrong truck out of camp, he would not be held liable for missing his transfer flight. Andy departs with his squad and with Kirby goes to work on the damaged train. Just as Kirby and Andy restart the engine, another train appears on the opposite track, carrying enemy soldiers, who open fire on the wounded. Kirby is hit and as he collapses, calls Andy and, handing him a letter, asks him to deliver it for him. Andy drives the train away to safety as Kirby dies. Andy is transferred back to the States, where he visits Kirby's family and reads Kirby's letter out loud to his two young children. In the letter, Kirby apologizes for not being with his children as they grow up, but explains that he felt obligated to fight for freedom in order to give them a better future.
