Shoop, Robert L. “Stephen Roskill, The Secret Capture: U-110 and the Enigma Story (Robert L. Shoop)”. The Northern Mariner / Le marin du nord 31, no. 4 (July 19, 2022): 472–474. Accessed November 23, 2024. https://tnm.journals.yorku.ca/index.php/default/article/view/904.