The Man Who Never Was (1956)

British Intelligence during World War II is trying to get the German High Command to shift its forces away from Italy prior to the invasion. To create the illusion that Britain is in fact planning to invade Greece, they plan to procure a dead body, plant secret papers on it, and arrange for the Spanish authorities to find it and send the papers on to the Germans. That's the plan, anyway. First they have to find a body that will look drowned, then create an identity for it that will pass German scrutiny. Based on a true story.