Mincemeat swallowed whole

In 1943 the body of Major Martin, a British serviceman, washed up on the shores of southern Spain. A local fisherman found the body, noticed the military attire, and the fact that a briefcase was chained to it. He decided to report it to the authorities.

Because Franco's government was in collusion with the Nazis, the body was turned over to the Abwehr, the Nazi's intelligence organization. The Abwehr examined the belongings found on the corpse, and what they discovered were documents too sensitive to send via regular courier, documents detailing plans for an allied invasion of Italy. The man had been wearing a life preserver and all clues pointed to an airplane accident at sea. Weary of a ruse, they examined and considered every last detail – things like love letters, theater tickets and overdue bills were enough to convince them that the corpse, and the documents it was carrying, were real.

It wasn't until well into the second week of the Allied invasion of southern Italy that they realized they had been duped. Major Martin was a fictitious character, and the documents he was carrying were part of an elaborate plan to divert the Axis powers' forces away from Sicily, where the Allies intended to land. "Operation Mincemeat" was a success.

That’s my quick summary of this fantastic article from Damn Interesting, one of my favorite websites. It's well worth the read.

More info on Wikipedia. And, for added trivia, here’s a link to a web page about Ian Fleming, of “shaken, not stirred" fame. According to this article Fleming himself directed “Operation Mincemeat”. This, however, contradicts both the Damn Interesting article and the Wikipedia article.