Herbert Yardley
He built American signals intelligence from scratch — then blew it all open in a bestselling book.
Herbert Yardley
Herbert Yardley was the founder of American signals intelligence — a self-taught cryptographer from Indiana who talked his way into Army intelligence in WWI and built America's first permanent codebreaking organization. The 'American Black Chamber' (officially the Cipher Bureau) operated 1919–1929 in New York, funded jointly by the State Department and the Army. Its greatest success was reading Japanese diplomatic traffic during the 1921–22 Washington Naval Conference, giving American negotiators advance knowledge of Japan's bottom-line positions. In 1929, Secretary of State Henry Stimson closed the bureau — reportedly saying 'Gentlemen do not read each other's mail.' Two years later, Yardley published everything.
Why This Person Matters
Yardley's significance is twofold and paradoxical. He created American signals intelligence — transforming the ad-hoc WWI code-cracking units into a permanent professional organization — and he destroyed it by publishing its methods and successes in a bestselling 1931 book. His publication caused Japan to change its diplomatic codes immediately; it prompted congressional hearings; and it helped motivate the Communications Act of 1934 (which criminalized publication of intercepted communications). His rehabilitation began in WWII when he worked for the RCMP and later for other Allied agencies, and was completed posthumously when later declassification confirmed the broad accuracy of his 1931 claims.
Yardley joined the State Department as a telegraph code clerk, quickly recognized vulnerabilities in US diplomatic codes, and wrote a paper demonstrating he could read the President's messages. Promoted to Army intelligence (MI-8) in WWI, he ran a code-and-cipher section that broke German, Mexican, and other traffic. After the Armistice he persuaded both the Army and the State Department to fund a permanent joint bureau — unprecedented in American history — located in a Manhattan brownstone. The operation read the traffic of 20 nations over its decade of operation.
The 1921 Washington Naval Conference negotiated the first major international arms limitation treaty — establishing ratios for capital ship tonnage among the great powers. The American delegation, briefed daily by Yardley's team on Japan's diplomatic instructions to its negotiators, knew in advance the maximum concessions Japan would accept. The US successfully pushed Japan to accept a 10:10:6 capital ship ratio rather than the 10:10:7 Japan was authorized to demand. This is among the clearest documented cases of intelligence-enabled diplomatic advantage in American history.
The American Black Chamber (1931) was a bestseller — Japan read it immediately and changed its diplomatic codes within months. Congress held hearings. The Communications Act of 1934 criminalized what Yardley had done. Japan's new codes (including the systems that became RED and then the M-97/PURPLE Typewriter machines) were specifically designed to be unreadable by the methods Yardley had disclosed. In a direct sense, Yardley's book created the cryptographic environment that required the US to develop the PURPLE-breaking MAGIC program — the very system that should have warned of Pearl Harbor.
| Born | April 13, 1889, Worthington, Indiana |
| Died | August 7, 1958, Washington, D.C. |
| Organization | MI-8 (WWI) → American Black Chamber (1919–1929) |
| Key Break | Japanese diplomatic codes — Washington Naval Conference 1921 |
| Controversy | Published The American Black Chamber (1931) |
| Impact | Caused the US to close the Black Chamber; Japanese code changes |
| Later | RCMP codebreaker WWII; NSA precursor work; novelist |