Bird, Keith W., and Jason Hines. βIn the Shadow of Ultra: A Reappraisal of German Naval Communications Intelligence in 1914-1918β. The Northern Mariner / Le marin du nord 28, no. 2 (November 30, 2018): 97β117. Accessed April 4, 2025. https://tnm.journals.yorku.ca/index.php/default/article/view/191.