During Operation Market-Garden, the Allied invasion of Holland in September 1944 (fourteen months after Operation Mincemeat and the invasion of Sicily), a British staff officer brought a complete Corps-level operations order with maps and graphics, which was never supposed to leave Britain, with him on a transport glider and then inadvertently left it on the glider when it landed in Holland. The Germans eventually overran the glider landing zone and found the operations order. But due to Operation Mincemeat, they were so convinced that this was another set of fake documents planted for deception by the British, and actually maneuvered contrary to what the documents indicated for the first few days of the battle. This was included in Un puente demasiado lejos (1977), about Operation Market-Garden.
In this movie, Lieutenant Commander Ewen Montagu (Clifton Webb) selects a man who had died of pneumonia, because the corpse would need to have similarly damaged lungs if it had really drowned. There is also a very emotional scene where the man's father is persuaded to allow his son to be used for the deception. In fact, a Welsh vagrant, both of whose parents were dead, was used, and his death was due to his probably accidentally eating a piece of discarded bread spread with rat poison, being homeless and starving at the time. It was judged to make it almost impossible to tell that this, rather than drowning, was the real cause of death. The identity of "the man who never was" was a closely guarded secret until 1998, when it was discovered that he was called Glyndwr Michael. His grave in Huelva, Spain (near the beach at Punta Umbria) now uniquely carries both his fictional and real names.
In a rare straight role, an uncredited Peter Sellers impersonated the voice of British Prime Minister Sir Winston Churchill. Peter Sellers can also be heard as the voice coming over the airfield speaker during the parachute demonstration and, very briefly, as the voice of an unseen taxi driver.
The quote that opens and closes the movie, "Last night I dreamed a deadly dream, beyond the Isle of Skye, I saw a dead man win a fight, and I think that man was I" is from the song "The Battle of Otterburn," Child Ballad #161 and appears in a manuscript dated circa 1550. The original reads, "But I hae (have) dreamed a dreary dream, Beyond the Isle of Skye; I saw a dead man win a fight, And I think that man was I."
Ewen Montagu, the officer who was in charge of Operation Mincemeat, has a small cameo role as an Air Marshal.