Operation Bernhard was the codename of a secret Nazi plan devised during the Second World War by the RSHA and the SS to destabilise the British economy via economic warfare by flooding the global economy and the British Empire with forged Bank of England £5, £10, £20, and £50 notes. It was the largest counterfeiting operation in the history of economic warfare.
During World War II the Nazis almost destroyed the credibility of the British pound sterling by producing near-perfect forgeries. In total, the Nazis produced counterfeit sterling notes with a face value of £134 million, equivalent to ten percent of all sterling in circulation at that time.
The British government ultimately had to issue two recalls of all pound notes — fake and genuine — bigger than £5 and issue fresh notes, which had an added security feature: a metal strip.