From the Ground Up: American Cryptology during World War I . Vol. 48. Series II: World War I. Ft. George G. Meade, MD: National Security Agency, Center for Cryptologic History. https://media.defense.gov/2023/Jan/26/2003150273/-1/-1/0/WWI_BOOK_01192023.PDF Accessed 01 February 2023

John F. Dooley. From the Ground Up: American Cryptology during World War I . Vol. 48. Series II: World War I. Ft. George G. Meade, MD: National Security Agency, Center for Cryptologic History. https://media.defense.gov/2023/Jan/26/2003150273/-1/-1/0/WWI_BOOK_01192023.PDF Accessed 01 February 2023. Cryptologia, 48(1):91-94, January 2024. [doi]