1. Ellis Zacharias ,Secret Missions: The Story of an Intelligence Officer( New York : Van Rees Press , 1946 ), pp. 5 – 6 .
2. The Rise and Fall of the Office of Naval Intelligence, 1882-1892: A Technological Perspective
3. Statement of Rear Admiral Richard P. Niblack, 7 January 1920,Hearing before the Subcommittee of House Committee on Appropriations, Sixty Sixth Congress Second Session (Washington, DC : Government Printing Office , 1920), pp. 1013–1018.