This is the true story of M.E. Clifton James, who bore an uncanny resemblence to General Montgomery.
He was seen at a London theatre performing as Monty at the End of a review and was so like him that British Intelligence decided to use him to Fool the Nazi Army that our D-Day would come from Africa and not Normandy. He plays himself in the film.
If you've never watched a war movie watch this, you won't be disappointed.