The film opens at the US Marine training ground of Parris Island, South Carolina. Gunnery Sergeant Hartman introduces himself and begins a tirade of abuse and name-calling to each of the recruits. The nicknames Sgt. Hartman gives to each of the characters stays with them throughout the film.
Hartman focuses his abuse on Private Joker, Private Cowboy and Private Pyle. Joker makes a comment under his breath at Hartman. Hartman incensed, grabs hold of Cowboy. Joker admits it was him and Hartman punches him in the stomach. Hartman then focuses on Private Leonard Lawrence. Hartman makes fun of his obesity and nicknames him Gomer Pyle. He then chokes Private Pyle for laughing during his tirade.
Much of the focus during training camp is on Private Pyle’s inability to get in step with the other soldiers. He is constantly lagging behind and disobeying the rules. Hartman is hard on Pvt. Pyle in order to get him to up to speed, then ultimately gives up and in punishes the platoon for not motivating Pvt. Pyle.
Pvt. Pyle is then held down and beaten by members of the platoon as a last resort to get Pyle to fall in line. Pyle does eventually shape up, but his demeanor changes. He begins to daydream and stare off into space. His mental state goes from a happy-go-lucky type to a person defeated by his position in life. After graduation Joker is assigned night watch and discovers Pyle in the restroom loading his rifle. Pyle begins screaming the Rifleman’s Creed and wakes up Hartman. Pyle then kills Hartman and turns the gun on himself.
The film flashes forward to Vietnam. Joker is now a combat correspondent for Stars and Stripes magazine. He is sent on a mission to cover 1 Platoon. Here he meets up with his boot camp friend Cowboy and follows his platoon into the city of Hue. Most of the platoon’s battles occur in Hue or along the Perfume River as they fight to gain control of the city and are held up by sniper fire.