Yardley's Codebreaking of a Chinese Book Cipher (1939)

Herbert O. Yardley wrote The Chinese Black Chamber after Word War II, posthumously published in 1983. It describes his days in China from 1938 to 1940, where he was invited by the Chiang Kai-shek's government to work on Japanese codes and ciphers. Codebreaking of one particular cipher is described in some detail, which I described in a new article, "Yardley's Codebreaking of Book Cipher used by Pro-Japanese Traitors in China (1939)".