Much of American history has been redacted. Since the World War 2, the number of secrets the US government has kept has grown exponentially. There are some things they think are too dangerous for the public to know. Matthew Connelly, author of the Declassification Engine, takes Don through America's top secrets of the 20th century.

Produced by Benjie Guy. Mixed by Stuary Beckwith. Senior Producer: Charlotte Long.

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