I Was Monty's Double (released in the US as The Counterfeit General Montgomery[1]) is a book by M. E. Clifton James, first published in London in 1954.

It was made into a film in 1958, directed by John Guillermin, from a screenplay adapted by Bryan Forbes.

It tells the story of Operation Copperhead: James had an uncanny resemblance to Bernard Montgomery in real life, and he was used to impersonate Montgomery to confuse the Germans during the Second World War.

James/Montgomery deliberately talked nonsense about non-existent operations and plans, in the hope that the spies would overhear and take such information seriously.

According to some accounts, the plan was brought to an abrupt end when James, still in disguise as Montgomery, was seen in public drunk and smoking, while the real Montgomery was a teetotaling non-smoker.