The film is divided in three parts. The first takes place prior to the war where cocky Philadelphia steel worker and "Man's man" Al Schmid (John Garfield) despises the idea of marriage and losing his independence until he meets his match in Ruth Hartley (Eleanor Parker). Ruth takes no nonsense from him and impresses Schmid by enjoying a hunting trip he takes her on.
The 17-year-old Ira Hamilton Hayes has never been off the Pima reservation in Arizona when he enlists in the United States Marine Corps to serve his country in World War II.
Pilot Officer Peter Penrose (John Mills) is posted in the summer of 1940 as a pilot to (the fictional) No. 720 Squadron, at a new airfield, RAF Station Halfpenny Field, as a very green "15-hour sprog" Bristol Blenheim pilot and is assigned to B Flight, under Flight Lieutenant David Archdale (Michael Redgrave).
While returning from a World War II bombing mission, a United States Army Air Forces B-25 Mitchell bomber sustains damage from action with German fighters. Without any order to abandon the aircraft, the navigator, Hamner (Basehart), panics and bails out. The aircraft, now lost due to having no navigator, and the remaining crew overfly their base and continue on for another 700 miles before eventually crash landing in the Libyan desert.
Carl Brashear (Gooding, Jr.) leaves his native Kentucky and the life of a sharecropper in 1948 by joining the United States Navy. As a crew member of the salvage ship USS Hoist, where he is assigned to the galley, he is inspired by the bravery of one of the divers, Master Chief Petty Officer Leslie William "Billy" Sunday (De Niro). He is determined to overcome racism and become the first black American Navy diver, even proclaiming that he will become a master diver. He eventually is selected to attend Diving and Salvage School in Bayonne, New Jersey, where he arrives as a boatswain's mate second class. He finds that Master Chief Sunday is the leading chief petty officer and head instructor, who is under orders from the school's eccentric, bigoted commanding officer to ensure that Brashear fails.
The film opens showing Louis "Louie" Zamperini flying as a bombardier of a United States Army Air Forces B-24 Liberator bomber, during an April 1943 bombing mission against the Japanese-held island of Nauru. The plane is badly damaged in combat, with a number of the crew injured. The hydraulics of the plane are shot and damaged, but the pilot, Phil, manages to bring it to a stop at the end of the runway thanks to a flat tire.
A French unit on patrol in Vietnam in 1954, during the final year of the First Indochina War, is ambushed by Viet Minh forces. Viet Minh commander Nguyen Huu An orders his soldiers to "kill all they send, and they will stop coming".
In 1959, United States Navy Rear Admiral Matt Sherman (Cary Grant), ComSubPac, boards the obsolete submarine USS Sea Tiger prior to her departure for the scrapyard. The first commanding officer of the Sea Tiger, Sherman begins reading his wartime personal logbook and recalling earlier events
The film begins with Ron Kovic's childhood during the summer of 1961 in Massapequa, Long Island, New York. He plays war in the woods, attends a Fourth of July parade, plays and wins at a local neighborhood baseball game, and watches President John F. Kennedy's inaugural address, which later inspires him to enlist in the Marines.
A warrior without a war, Lt. Col. "Bull" Meechum, a pilot also known as "The Great Santini" to his fellow Marines, moves his family to the military-base town of Beaufort, South Carolina in peacetime 1962. His wife Lillian is loyal and docile, tolerant of Meechum's temper and drinking. Their teenaged kids, Ben and Mary Anne, are accustomed to his stern discipline and behave accordingly, while adapting to their new town and school.
In February 1942, just two months after the Pearl Harbor attack, the United States Army Air Forces plan to retaliate by bombing Tokyo and four other Japanese cities—taking advantage of the fact that US aircraft carriers can approach near enough to the Japanese mainland to make such an attack feasible.
John Wayne stars as U.S. Navy Captain Rockwell "Rock" Torrey, a divorced "second generation Navy" son of a career Chief Petty Officer. A Naval Academy graduate and career officer, Torrey is removed from command of his heavy cruiser for "throwing away the book" when pursuing the enemy and then being torpedoed by a Japanese submarine shortly after the attack on Pearl Harbor. Kirk Douglas portrays Torrey's executive officer, Commander (later Captain) Paul Eddington, a wayward sort of career officer who has resigned as a naval aviator and returned to the surface navy because of an unhappy marriage. His wife's numerous affairs and drunken escapades have become the talk of Honolulu and her death during the Pearl Harbor attack—in the company of an Army Air Corps Officer (Hugh O'Brian), with whom she had just had a wild fling on a local beach—drives Eddington into a bar brawl with a group of other Army Air Corps officers, a subsequent stint in the Pearl Harbor brig, and exile as the "... officer in charge of piers and warehouses ..." in what he calls a "backwater island purgatory.
Sam Cahill (Tobey Maguire) is a Marine captain about to embark on his fourth tour of duty. He is a steadfast family man married to his high school sweetheart, Grace (Natalie Portman), and he has two young daughters, Isabelle and Maggie (Bailee Madison and Taylor Geare). Sam's brother Tommy (Jake Gyllenhaal) is being released from jail for an armed robbery, before Sam departs for Afghanistan in October, 2007. News comes that Sam's helicopter has crashed over the water, killing all of the Marines aboard. In reality, he and a hometown friend, Private Joe Willis (Patrick Flueger), have been taken prisoner in a mountain village.