Sale, Tony, ed. (1940). Der Schlüssel M Verfahren M Allgemein [The Enigma General Procedure] (PDF). Berlin: Supreme Command of the German Navy. Retrieved 26 November 2009 – via Bletchley Park.
Erskine 2006, p. 59 Erskine, Ralph (December 2006), "The Poles Reveal their Secrets: Alastair Denniston's Account of the July 1939 Meeting at Pyry", Cryptologia, vol. 30, no. 4, pp. 294–305, doi:10.1080/01611190600920944, S2CID13410460
Erskine 2006, p. 59 Erskine, Ralph (December 2006), "The Poles Reveal their Secrets: Alastair Denniston's Account of the July 1939 Meeting at Pyry", Cryptologia, vol. 30, no. 4, pp. 294–305, doi:10.1080/01611190600920944, S2CID13410460
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Rex had been born Rudolf Stallmann in Berlin in 1871 and had changed his surname to that of his French wife, becoming "Rodolphe Lemoine" [fr]. Kahn 1991, p. 57. Kahn, David (1991), Seizing the Enigma: The Race to Break the German U-boat Codes, 1939-1943, New York: Houghton Mifflin Co., ISBN978-0-395-42739-2
Woytak 1988, pp. 497–500 Woytak, Richard (January 1988), "Colonel Kowalewski and the Origins of Polish Code Breaking and Communication Interception", East European Quarterly, XXI (4), Boulder: University of Colorado: 497–500, ISSN0012-8449
