US Marine Sgt John Basilone prepares to confront Japanese forces somewhere in the Pacific. Meanwhile, budding journalist Robert Leckie and Eugene Sledge enlist to serve for their country. Eight months after Pearl Harbor, the 1st Marine Division lands on Guadalcanal.

Sgt Basilone arrives in Guadalcanal, quickly earning the respect of his comrades for his leadership and valour in a series of skirmishes, but a naval bombardment and airfield assault pushes Basilone and his men to the limits of their endurance defending their territory.

The American soldiers arrive in Melbourne following their ordeal at Guadalcanal and are greeted as heroes by the Australian public. Leckie falls for a local woman, and Basilone is honoured for his bravery in battle but finds his new-found fame back home has a downside.

Eugene Sledge enlists in the Marines. Division are put into action at Cape Gloucester. Leckie and his comrades arrive in Pavuvu where they try to repel a Japanese attack, but adjusting to the jungle terrain and battling illness prove to be their greatest challenges.

Sledge and Leckie land with the 1st Marine Division at Peleliu. Sledge leaves America to join the forces in the south Pacific and has a harrowing introduction to combat when he participates in the assault on Peleliu. Back home, Basilone promotes the war bonds programme.

The Marines move to capture Peleliu's vital airfield. During battle, Leckie is wounded by a blast concussion while trying to relay a message to the corpsman and evacuated to a hospital ship. Sledge realises he is still far from accustomed to the brutal realities of war.

Sledge and the 5th Marines move into Peleliu's Bloody Nose Ridge to face the Japanese. Andrew "Ack-Ack" Haldane is killed by a Japanese sniper while assessing Hill 140. Back home, Basilone becomes disillusioned with selling war bonds and longs to rejoin his comrades.

A restless Basilone is transferred to the 5th Marine Division where he trains Marines for combat. There he meets and marries Sgt Lena Riggi. Called to lead his traniees into battle on Iwo Jima, Basilone is killed by shrapnel from a Japanese mortar shell.

Sledge and the 1st Marines land at Okinawa. Sledge, now a seasoned veteran, becomes more cynical and no longer shows any compassion for the Japanese. As he and others prepare to return home, they hear of a "new bomb" that vaporised an entire city in the blink of an eye.

The Marines return home following the Japanese surrender but a demoralised Sledge struggles to cope with the horrors he saw. Leckie's relationship with his parents deteriorates, and Lena meets John Basilone's family for the first time and gives them his Medal of Honor.