Synopsis
Operation Mincemeat involved the acquisition and dressing up of a human cadaver as a "Major William Martin, R.M." and putting it into the sea near Huelva, Spain. Attached to the dead body was a brief-case containing fake letters falsely stating that the Allied attack would be against Sardinia and Greece rather than Sicily, the actual point of invasion. When the body was found, the Spanish Intelligence Service passed copies of the papers to the German Intelligence Service which passed them on to their High Command. The ruse was so successful that the Germans still believed that Sardinia and Greece were the intended objectives, weeks after the landings in Sicily had begun.
The screenplay of the film stayed as close to the truth as was convenient, with the remainder being fiction. For example, the Irish spy in the film is complete fabrication. Ewen Montagu declared that he was happy with the fictitious incidents which, although they didn't happen, might have happened. During filming, Montagu has a cameo role, that of an Air-Vice Marshal who has doubts about the feasibility of the proposed plan. It was described as a "surreal" moment when the real Montagu addresses his fictional persona, played by Webb.
Read more about this topic: The Man Who Never Was