There was a movie made perhaps in the 50's but as late as the 70's. The plot: time frame is WW2 and the allies have to make the Natzi's think that an invasion is going to happen in one place when it's actually happening in another, so they dump a corpse dressed as an allied soldier with "clues" in part of the ocean where they know the body will end up on a beach and be found by the Natzi army. [could be based on a real incident or maybe that's a rumor]. I keep thinking the title is "The man who wasn't there" but in IMDB a noir Billy Bob Thornton movie comes up.
It's from the 60s, called, 'The Heroes of Telemark' with Kirk Douglas and Richard Harris. And it IS in fact based on actual events. In fact, recently (and I mean like 2 weeks ago) PBS did this great documentary about the whole caper, and retrieving the heavy water 60 years later.