There is a book called "Ghost Soldiers" which the movie is based on. The book is about soldiers on the Bataan Death March, and the soldiers that came to rescue them. Alternating chapters follow the lives of men in each group. The opening scene depicts a gruesome scene.

The Japanese had made American POWS dig air raid trenches (that were covered with wood). One day, the air raid sirens go off so the POWS rush to their assigned trenches. But no bombers or planes could be heard. The Japs poured gasoline over the trenches and lit them up. POWS that tried to run were shot. However, one trench was near the edge of a cliff that had some sort of ravine in it running down to a beach. The Japs didn't know that the Trench connected to this. Several POWS managed to escape this way and tried to hide on the beach. I think that all but two were shot when a patrol came looking for them. The two that survived managed to make it out and this is how we know this story.

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