The Secret Life of John and Alice

During the Second World War, making of Spitfires was so secret that one married couple didn't know they were both working on it. They found out decades later at a dinner party in the 1970s. A factory in Southampton which made most of the Spitfires was bombed in 1940 by the Luftwaffe. It needed to be kept safe from bombing raids and divided up into tiny micro factories around the place. This came out decades after the war that this is how it had been done, basically.