Hitler’s lightning-fast advances across Europe in the early months of World War II led to suspicions that he owed his victories to “fifth columns” of traitors: Nazi sympathizers who compromised their countries’ defenses from within through spying and sabotage. Those suspicions—widespread but erroneous—led officials in Britain, including Winston Churchill, to wonder whether the same could happen there.
Suspicion fell upon Sir Oswald Mosley, formerly a wunderkind of mainstream British politics who had become enamored of fascism in the 1930s. He founded the British Union of Fascists, later renamed simply the British Union. By the start of the war, Mosley’s was barely a fringe movement, but it could still do damage if it were harnessed to the German war effort. In May 1940, Mosley and hundreds of his followers, accused of no crimes, were rounded up and interned.
