MI-8 closed its doors for good on October 31, 1929, just two days after the stock market crashed. With Yardley's esoteric skills in very low demand, and no government pension due to his secretly funded work, he took up writing about his experiences in codebreaking to support his family. His memoirs, "The American Black Chamber", were published by Bobbs-Merrill in 1931. The book outlined the history of the first U.S. Signals Intelligence (SIGINT) organization, described the activities of MI-8 during World War I and the American Black Chamber in the 1920s, and illustrated the basic principles of signals security.