How is music important to the film Letters Home from Vietnam?

How is music important to the film Letters Home from Vietnam? How is music important to the soldiers and the history of the Vietnam War itself? (Answer in a paragraph of at least 5 sentences)
Movie Link: https://drive.google.com/file/d/119xbMiqtbBttOgNa6Jh2Ii-vqInh_y-y/view

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