'The American Black Chamber' (1931) by Herbert O. Yardley is a groundbreaking, sensational memoir exposing the secrets of the U.S. government's first, clandestine peace-time code-breaking unit, the "e;Black Chamber,"e; which he led. The book chronicles how his team intercepted and solved foreign diplomatic messages and highlights the early role of cryptanalysis in U.S. diplomacy. It details the methods used to break codes, secure intercepted cables from private companies like Western Union, and the intelligence gathered, such as during the Mexican Revolution and the Washington Conference. The book highlights the tension between intelligence gathering and diplomacy, famously highlighting the incident when Secretary of State Henry L. Stimson cut funding for the agency, declaring that "e;gentlemen do not read other people's mail"e;. It caused a major scandal by revealing American capabilities and was believed to have prompted Japan to strengthen its own cryptographic security, costing the U.S. in the Pacific during World War II. Known as a pioneering work of non-fiction spy literature, it detailed how Yardley s team decoded over 45,000 telegrams.