Physically and mentally debilitated after the four-month ordeal on Guadalcanal, Leckie, Basilone and thousands of their comrades land in Melbourne, where they are greeted by adoring crowds and viewed as the saviors of Australia. While his buddies carouse, Leckie becomes deeply attached to an Australian woman and her first-generation Greek family. Meanwhile, Basilone is awarded the Medal of Honor and is asked to return home to help sell U.S. war bonds.

Finally enlisted as a Marine, Sledge trains for combat at Camp Elliott. The 1st Marine Division lands at Cape Gloucester on the Japanese-held island of New Britain. As Leckie and the other Marines battle the Japanese, they quickly realize that the more ominous enemy is the smothering jungle itself. Having survived Gloucester and stationed on the godforsaken island of Pavuvu, Leckie begins displaying the physical and mental effects of combat and is sent to a naval hospital on nearby Banika for psychiatric observation.

Increasingly frustrated by his role campaigning for war bonds, Basilone convinces the Marines to allow him to train troops headed for combat. Transferred to Camp Pendleton, he enjoys a whirlwind romance with an initially reluctant female Marine, Lena Riggi. But the couple know they are living on borrowed time, as Basilone is soon to take part in the Marine landing on Iwo Jima.

After battling across the island of Okinawa for more than a month, Sledge and the rest of the 1st Marine Division are ordered to relieve an Army division that has been in combat against the most strongly defended Japanese position on the island. The primordial conditions and the moral dilemma posed by the presence of civilians put tremendous strain on the physical and psychological endurance of Sledge and the other Marines.

After the Japanese surrender, Leckie, healed from his wounds, leaves the hospital and returns home, while Sledge heads back to Alabama to be reunited with his family and Sid Phillips. Lena visits Basilone’s home and has an emotional meeting with his family. Leckie adjusts to post-war life by resuming his old job and starting a new relationship, but for Sledge, unsure why he survived the war seemingly unscathed, adjustment will require more time.