Chris Spackman's NeoCities Page

The American Black Chamber

Inspired by Room 40's success with the Zimmermann Telegram, the United States built its own codebreaking organization during World War I. Under Herbert O. Yardley, it grew from a small wartime unit into a peacetime intelligence bureau that scored one of the greatest cryptanalytic coups in American history — and was then shut down in a fit of principle.

MI-8: America's First Codebreakers

In June 1917, just two months after the US entered the war, a 28-year-old State Department code clerk named Herbert O. Yardley convinced the War Department to create a codebreaking unit. Designated MI-8 (Military Intelligence, Section 8), it was tasked with breaking enemy codes and creating secure American codes.

Yardley was largely self-taught. As a State Department telegrapher, he had amused himself by breaking the codes used in President Wilson's own diplomatic messages — and was alarmed by how easy it was. He wrote a 100-page memorandum arguing that the US needed a dedicated cryptanalytic bureau, and the Army agreed.

By the end of the war, MI-8 had grown to about 150 people. They broke codes used by Germany, Spain, and other nations, and developed new code systems for the American military. But when the war ended in November 1918, the question became: what happens to MI-8?

The Cipher Bureau (1919 – 1929)

Yardley argued that the US needed a permanent peacetime codebreaking bureau. The War Department and the State Department agreed to jointly fund it. The new organization was officially called the Cipher Bureau, but it later became known by its more dramatic name: the Black Chamber.

The Cipher Bureau operated in secret from a brownstone in New York City, disguised as a commercial code company. Yardley and a small staff — never more than about 20 people — worked on breaking the diplomatic codes of dozens of nations.

The Washington Naval Conference

The Black Chamber's greatest triumph came during the Washington Naval Conference of 1921–1922. The major naval powers — the United States, Britain, Japan, France, and Italy — met to negotiate limits on warship construction, hoping to prevent a costly naval arms race.

Breaking the Japanese Codes

Yardley's team had been working on Japanese diplomatic codes for over a year before the conference began. The work was extraordinarily difficult — the Japanese used complex code systems, and few Americans could read Japanese. But by the time the conference opened, the Black Chamber could read Japan's diplomatic traffic.

Try It: Diplomatic Code Exercise

Diplomatic codes work differently from traditional ciphers. Instead of transforming individual letters, a codebook maps words and phrases to arbitrary code groups. Below is a simplified exercise. Try encoding a diplomatic message using the codebook, then decode someone else's message.

Encoded / Decoded Result

Diplomatic Codebook

Click a row to insert that word into your message.

The Negotiation Advantage

The decoded Japanese messages gave American negotiators an extraordinary advantage. The key issue at the conference was the ratio of battleships each nation would be allowed. The US and Britain proposed a 5:5:3 ratio — for every 5 capital ships the US and Britain could have, Japan would be allowed 3.

Japan's public position was that it needed a 10:10:7 ratio — 70% of the American and British fleets rather than 60%. But Yardley's team decoded secret instructions from Tokyo to the Japanese delegation:

Knowing Japan's real bottom line, the American negotiators refused to budge from 5:5:3 (equivalent to 10:10:6). The Japanese delegation, following their secret instructions, eventually agreed — exactly as their decoded messages said they would. The resulting Five-Power Treaty set the ratio the Americans wanted.

The Shutdown

In 1929, Herbert Hoover became President and appointed Henry L. Stimson as Secretary of State. When Stimson learned about the Black Chamber's activities, he was outraged. He withdrew the State Department's funding, effectively killing the organization.

The quote is famous, but the reality was more complicated. Stimson later served as Secretary of War during World War II, where he actively used intelligence from codebreaking — including the breaking of Japanese codes by the very organization (the Army's SIS, under William Friedman) that had been built to replace the Black Chamber. Context and circumstances, it seems, changed his view.

The Tell-All Book

Angry and unemployed, Yardley did something unprecedented: he wrote a book about it. The American Black Chamber, published in 1931, revealed in detail how the Cipher Bureau had broken the codes of Japan and other nations. It became a bestseller in both the US and Japan.

The consequences were severe:

• Japan overhauled its entire code system, undoing years of American cryptanalytic work.
• Congress eventually passed a law making it illegal to publish decoded diplomatic messages (sometimes called the "Yardley Act" of 1933).
• Yardley was shut out of government cryptographic work for the rest of his career.

Legacy

The Black Chamber's closure was not the end of American codebreaking — it was a transition. The Army quickly established the Signal Intelligence Service (SIS) under William Friedman, who brought a more scientific and mathematical approach to cryptanalysis. The SIS would eventually evolve into the National Security Agency (NSA).

Yardley's story illustrates tensions that remain relevant today: between security and privacy, between the usefulness of intelligence and the ethics of collecting it, and between government secrecy and the public's right to know.

Things to Try

• Use the codebook exercise above to encode a short diplomatic message. Then give just the numbers to a classmate and see if they can decode it.
• Try writing a message using words that are not in the codebook. What do you do? (This is one weakness of code systems.)
• Imagine you are the Japanese delegation. You discover your codes were broken during the conference. What do you do? What are the diplomatic consequences?
• Was Stimson right to shut down the Black Chamber? What arguments can you make for and against peacetime codebreaking between nations that are not at war?
• Was Yardley right to publish his book? Consider: the public's right to know, national security, the careers and safety of people involved, and the impact on foreign relations.