Spying on other nations has long been part of the global power game, but it has not always been considered proper diplomatic practice.
"Gentlemen do not read each other's mail," former U.S. Secretary of State Henry L. Stimson declared, having decided in 1929 to shut the first U.S. peacetime cryptanalytic organization, the Cipher Bureau.
Yet, despite Stimson's views, U.S. intelligence gathering continued, and with the outbreak of World War II the major powers became fully engaged in the silent war of codebreaking.