Operation Mincemeat was a successful British disinformation plan during the Second World War.
As part of Operation Barclay, the widespread deception intended to cover the invasion of Italy from North Africa, Mincemeat helped to convince the German high command that the Allies planned to invade Greece and Sardinia in 1943 instead of Sicily, the actual objective. This was accomplished by persuading the Germans that they had, by accident, intercepted “top secret” documents giving details of Allied war plans. The documents were attached to a corpse deliberately left to wash up on a beach in Punta Umbría in Spain. The success of the planting of false documents was confirmed through Ultra decrypts of German messages.
A similar story was coincidentally used as a plot device by Duff Cooper in his 1950 novel Operation Heartbreak. The true story was revealed in 1953, in the book The Man Who Never Was. A film of the same name was made in 1956.