one of the marks was that according the habit of the time the banknotes were pinned together to look authentic but either the prisoners working in the printing press or unaware spies put the pin in the place no Briton would put - through the face of the monarch or the coat of arms, I'm not sure now.
The other reason was that the prisoners actively sabotaged the printing, making little mistakes.
Trirain t1_ir9q01e wrote
Reply to comment by SatansMoisture in TIL about Operation Bernhard. During WWII, Germany attempted to bring about the collapse of the British economy by forging ≈£130 million in British bank notes. The notes are considered among the most perfect counterfeits ever produced, and are very difficult to differentiate from legitimate notes. by rkadeYT
one of the marks was that according the habit of the time the banknotes were pinned together to look authentic but either the prisoners working in the printing press or unaware spies put the pin in the place no Briton would put - through the face of the monarch or the coat of arms, I'm not sure now.
The other reason was that the prisoners actively sabotaged the printing, making little mistakes.
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There is a movie about prisoners who worked in the printing press made from a book which was written by an actual prisoner who survived it.