The National Security Agency’s latest declassification release consists of over 200 documents created by or about Herbert O. Yardley from between 1918 and 1968 (excluding 1924-1927). Many documents relate to Yardley’s years at MI-8, Military Intelligence’s wartime cryptologic section. Of special interest are documents from 1968 about NSA efforts to investigate claims that Yardley had been working for the Japanese.
Yardley headed MI-8 during World War I, and the Cipher Bureau (a.k.a. the Black Chamber) for several years following the war, excelling at breaking Japanese diplomatic messages. On October 31, 1929, the Cipher Bureau closed because of changing governmental priorities and policies. Desperately in need of money, Yardley resorted to writing a tell-all book, The American Black Chamber, which seriously affected communications security for many nations worldwide—including the United States. He would consequently live the rest of his life defending his actions and working as a cryptologic mercenary for whoever would hire him.
These documents enable a more nuanced view of a man otherwise noted for self-promotion and antiquated thinking. For example, through these documents, we learned that he was more aggressive in applying technology to his craft than otherwise believed. NSA is pleased to make this latest release available to the public.