In the Olympic trials at Randalls Island, Zamperini finished in a dead heat against world-record holder Don Lash and qualified for the 1936 Olympics in Berlin, Germany, though neither he nor Lash had much chance of winning the 5000 meter race. Zamperini has related several amusing anecdotes from his Olympic experience, including gorging himself on the boat trip to Europe. "I was a Depression-era kid who had never even been to a drugstore for a sandwich," he said. "And all the food was free. I had not just one sweet roll, but about seven every morning, with bacon and eggs. My eyes were like saucers.” By the end of the trip, Zamperini, in common with most athletes on the ship, had gained a good deal of weight - in Zamperini's case, 12 pounds. While the weight gain was not advantageous for his running it was necessary for his health, as he had lost 15 pounds while training in the summer heat in New York for the Olympic Trials.

Zamperini finished eighth in the 5000 meter distance event at that Olympics, but his final lap of 56 seconds was fast enough to catch the attention of Adolf Hitler, who insisted on a personal meeting.^[8] As Zamperini tells the story, Hitler shook his hand, and said simply "Ah, you're the boy with the fast finish."^[9] According to a profile on Bill Stern's Sports Newsreel radio program, Zamperini climbed a flag pole during the 1936 Olympic games and stole the personal flag of Hitler.

Zamperini enlisted in the United States Army Air Forces in September 1941,^[11] and earned a commission as a second lieutenant the following August. He was deployed to the Pacific island of Funafuti as a bombardier assigned to a B-24 Liberator bomber which he and his crew named "Super Man." In April 1942, Super Man was badly damaged in combat during a raid on the Japanese held island of Nauru and Zamperini and his crewmates were transferred to Hawaii to await a new assignment. On May 27, 1943, he and his crew were assigned to conduct a search for a lost aircraft and its crew. They were given another B-24, The Green Hornet, notorious among the pilots as a defective "lemon plane'. While on the search, mechanical difficulties caused the plane to crash into the ocean 850 miles west of Oahu, killing eight of the eleven men aboard.

The three survivors (Zamperini, along with pilot Russel Allen "Phil" Phillips and tail-gunner Francis "Mac" McNamara), with little food and no water, subsisted on captured rainwater and small fish eaten raw. They caught an albatross and used some of its meat to catch fish, all while fending off constant shark attacks and nearly being capsized by a storm.^[12] They were strafed multiple times by a Japanese bomber, puncturing their life raft; miraculously, no one was hit. McNamara died after thirty-three days at sea.

On their 47th day adrift, Zamperini and Phillips reached land in the Marshall Islands^[13] and were immediately captured by the Japanese Navy. Both Phillips and Zamperini were held in captivity and severely beaten and mistreated until the end of the war in August, 1945. Zamperini was held in the Japanese Prisoner-of-war camp at Ufuna for captives who were not registered as prisoners of war (POW). He was especially tormented by sadistic prison guard Mutsuhiro Watanabe (nicknamed "The Bird"), who was later included in General Douglas MacArthur's list of the 40 most wanted war criminals in Japan. Held at the same camp, was then-Major Greg "Pappy" Boyington, and in his book, Baa Baa Black Sheep, he discusses Zamperini and the Italian recipes he would write to keep the prisoners' minds off the food and conditions.