no duff

Origin: From the RAF slang expression "duff gen" meaning bad or fake information; "no duff", by extension means "accurate", also: "stop operations until ordered otherwise". It comes from the term "No Direction Finding" in the British Army in regards to radio/signals procedure. It was used when in training or on exercise to pass a message true in nature but not related to the aims of the exercise. This could be an accident, change of exercise requirements, etc. This means the message to be sent should not be subject to radio direction finding to locate the transmitting station by either the blue or. Origin information sourced from Wiktionary contributors (CC BY-SA 4.0).