The Black Chamber
The nickname of the American cipher bureau Herbert Yardley ran through the 1920s, shut down in 1929.
"The Black Chamber" was the nickname of the American cipher bureau that Herbert Yardley built from 1917. In the 1920s it read Japanese diplomatic codes, which made it effective but hardly secret. It was closed in 1929, when Secretary of State Henry Stimson decided that "gentlemen do not read each other's mail".
Two years later Yardley published The American Black Chamber, a detailed account of the work. The book drew attention to the bureau and made it better known than it ever was while it operated.