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The Cipher Bureau otherwise known as The Black Chamber was the United States' first peacetime cryptanalytic organization, and a forerunner of the National Security Agency. The only prior codes and cypher organizations maintained by the US government had been some intermittent, and always abandoned, attempts by Armed Forces branches prior to World War I.
Headed by Herbert O. Yardley (1889–1958), it was founded in May 1919 following World War I.  Yardley had commanded the Army cryptographic section of Military Intelligence (MI-8) during World War I. MI-8 was disbanded after the war. Jointly funded by the Army and the State Department, the Cipher Bureau was disguised as a New York City commercial code company; it actually produced and sold such codes for business use. Its true mission, however, was to break the communications (chiefly diplomatic) of other nations. Its most notable known success was during the Washington Naval Conference during which it aided American negotiators considerably by providing them with the decrypted traffic of many of the Conference delegations, most notably the Japanese.
In 1929, the State Department withdrew its share of the funding, the Army declined to bear the entire load, and the Black Chamber closed down. In his much later memoirs, then new Secretary of State Henry L. Stimson said that: "Gentlemen do not read each other's mail." His views on the worth of cryptanalysis had changed by the time he became Secretary of War during World War II, before and during which he, and the entire US command structure, relied heavily on decrypted enemy communications.
In 1931, and in need of money, Yardley wrote a book about the Cipher Bureau, entitled The American Black Chamber.
The term "Black Chamber" predates Yardley's use of it in the title of his book. Codes and code breakers have been used throughout history, notably by Sir Francis Walsingham in Elizabethan England. A so-called cabinet noir was established by King Henry IV of France in 1590 as part of the Poste aux Lettres. Its mission was to open, read and reseal letters, and great expertise was developed in the restoration of broken seals. In the knowledge that mail was being opened, correspondents began to develop systems to encrypt and decrypt their letters, the breaking of these codes giving birth to modern systematic scientific code breaking. The Black Chambers survived through to the Twentieth Century in a variety of guises and inspired similar organisations in other countries, such as the "Secret Office" of the British Post Office, and it is within this historical framework that Yardley uses the term.