This is a spy movie with Michael Caine in a bit part. The lovely Gia Scala, shown above, plays the principal love interest, and Jack Hawkins is the star. The story is supposedly true. The Brits somehow during WWI have the foresight to plant a sleeper agent in the German military. He rises to the rank of Lieutenant General, and is responsible for logistics, particularly during the Bulge. At the end of the war the agent is repatriated to Britain.
Various comments on IMDB, and the lack of any other information suggest that this allegedly true story is false. If that is the case, and this is pure speculation on my part, and I’m not emotionally vested in it, then I think it’s possible that this may be a cover for Ultra intelligence. It would explain how the Allies knew various secrets pertaining to troop movements and supply without revealing that they were actually reading the German’s mail.
It can be seen in retrospect that certain things were hinted at in fiction. For example, the plot of From Russia With Love, which uses the Lektor coding machine as the McGuffin, is a sexed up version of the procurement of the Enigma machine prior to WWII. So it may be that the use of a fictional sleeper agent was part of what has been called a Bodyguard of Lies.
Update: The text below is encoded using a program that simulates the Enigma machine. The machine is a three rotor machine, and the initial rotor settings are an acronym that was used in Alias, Season 5. I’ve got a picture of the plug settings somewhere, but anyone who wants to try to crack it is welcome to try.