Herbert Osborne Yardley (April 13, 1889 – August 7, 1958) was an American cryptologist best known for his book The American Black Chamber (1931). The title of the book refers to the Cipher Bureau, the cryptographic organization of which Yardley was the founder and head. Under Yardley, the cryptanalysts of The American Black Chamber broke Japanese diplomatic codes and were able to furnish American negotiators with significant information during the Washington Naval Conference of 1921-1922. He later helped the Nationalists in China (1938–1940) to break Japanese codes. Following his work in China, Yardley worked briefly for the Canadian government, helping it set up a cryptological section (Examination Unit) of the National Research Council of Canada from June to December 1941. Yardley was le