that's... not what gp was talking about. Why are so many people jumping in with this mistake?

Operation mincemeat wasn't a german officer, it wasn't anything about using a known plaintext to compare to coded messages, it wasn't pretending to be german documents, and it wasn't to help with cryptanalysis. About the only similarity is a dead body

You're right. The while planting messages on bodies is what put me on the wrong track.