The movie opens with a marine (Robert Mitchum) floating in a rubber life raft, where he's clearly been for a long time. When he lands on a tropical island with a few thatch huts, he approaches cautiously with his knife drawn - only to find the area abandoned. He eventually finds there's only one other person on the island, the nun Sister Angela (Deborah Kerr). She's also there because of the actions of the Japanese. The two start to figure out how to live in their primitive surroundings. But then the Japanese take over the island, and they hide in a cave for days.
The movie is a character study of our two leads, Marine Corporal Allison and Sister Angela of the Roman Catholic Church. There are a number of Japanese on screen in short bursts, but they have no significant interactions with our two main characters - despite which, they're shown as human rather than stereotypical evil enemies. The acting by the two leads is great, and the film is beautifully constructed: a very good movie that deserves to be better remembered.