In March 1929 the newly appointed United States secretary of state, Henry Stimson, reportedly remarked that
“gentlemen do not read each other’s mail” when he closed down the State Department’s cryptographic unit. He had been shown Japanese intercepts and had been shocked to learn how they had been acquired. At that time the Black Chamber consisted of the veteran code breaker Herbert Yardley and a staff of five. Appalled by Stimson’s behavior, Yardley published his book, The American Black Chamber, in 1931 and revealed that his code breakers had for years read Japanese diplomatic telegrams. The Japanese Foreign Ministry promptly changed its cipher systems.