Sempill, Mitsubishi, and aviation intelligence

William Forbes-Sempill's importance extended beyond the official British aviation mission to Japan. His later consulting relationship with Mitsubishi and access to foreign aviation circles supplied technical ideas alongside Japan's own research. His enthusiasm for flying boats and torpedo bombers also encouraged Japanese interest in those aircraft. The exchange of ideas helped Mitsubishi compare different approaches without having to discover every possibility independently. British officials repeatedly recognized the security risk but hesitated to prosecute because intercepted Japanese communications supplied evidence that could expose their codebreaking. Combining domestic research with access to foreign work helped Japanese aircraft become more capable than outside observers expected.