Cryptologic History Calendar
1929: Cipher Bureau Closed.
After the organization disbanded, Yardley caused a sensation in 1931 with the publication of his memoirs of MI-8, "The American Black Chamber." In this book, Yardley revealed the extent of U.S. cryptanalytic work in the 1920s. Surprisingly, the wording of the espionage laws at that time did not permit prosecution of Yardley. (This situation was changed two years later with a new law imposing stiff penalties for unauthorized revelations of cryptologic secrets.) In a 1952 letter, William Friedman, a contemporary of Yardley, suggested, "In reading Yardley I recommend ingestion of liberal dozes of sodium chloride." (i.e., Take it with more than a grain of salt.)
Yardley did some cryptologic work for Canada and China during World War II, but he was never again given a position of trust in the U.S. government.
Read more about Herbert O. Yardley in "The Many Lives of Herbert O. Yardley on the NSA.gov site via the link below.