Army Security Agency: Notes on German High Level Cryptography and Cryptanalysis. European Axis Signal Intelligence in World War II, Vol 2, Washington (D.C.), 1946 (Mai), S. 2. Abgerufen: 24. August 2018. PDF; 7,5 MB (Memento vom 11. Juni 2014 im Internet Archive)
zdb-katalog.de
José Ramón Soler Fuensanta, Francisco Javier López-Brea Espiau und Frode Weierud: Spanish Enigma: A History of the Enigma in Spain. Cryptologia. Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 34.2010,4 (Oktober), S. 310. ISSN0161-1194.
José Ramón Soler Fuensanta, Francisco Javier López-Brea Espiau und Frode Weierud: Spanish Enigma: A History of the Enigma in Spain. Cryptologia. Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 34.2010,4 (Oktober), S. 313. ISSN0161-1194.