Future president John Kennedy fights to save his crew when their PT boat sinks in the Pacific.

In the early days of World War II, Lieut. (j.g.) John F. Kennedy arrives in the Solomon Islands to assume command of the battle-scarred PT 109. After making hasty repairs, he and his crew are sent to rescue a Marine patrol trapped on Choiseul. Though the mission is successful, the boat runs out of fuel and has to be towed back to base. Then, on the morning of August 2, 1943, while attempting to prevent the Japanese from landing troops at Vila, PT 109, having no radar equipment, is rammed and split in two by an enemy destroyer. Two of the men are killed, and Kennedy decides the only chance he and the other survivors have is to swim to a nearby island. One of the men is too badly burned to swim, and Kennedy tows him through the water. All efforts to make their location known fail until Kennedy writes a message on a coconut, which friendly natives take to nearby Rendova. They return with a canoe, hide Kennedy under palm fronds, and deliver him to an Australian coastwatcher. After directing the rescue of his men, Kennedy learns he is eligible for transfer home; instead, he elects to assume command of another PT boat.