Ludwig Stummel

Ludwig Stummel (5 August 1898 in Kevelaer – 30 November 1983 in Kronberg im Taunus) was a German career signals officer with the rank of Konteradmiral, who had a glass eye and a limp and who was in effect, the Chief of Staff of the Naval Warfare department, Naval Communications (4/SKL) of the Kriegsmarine. Stummel was most notable for being the person responsible for the cryptographical security of the Enigma cipher machine and Key M infrastructure security, during World War II. Stummel was replaced at the Kriegsmarine Naval War Command on the 16–17 August 1944 by Fritz Krauss, after becoming ill. Stummel was a fervent Catholic. His faith gave him a moral compass during the latter years of the war. Initially a supporter of Nazis,

Interwar period After undergoing a period of training at I. Naval Inspection, Stummel was transferred to I. Naval Brigade between January 1919 and June 1919, later becoming platoon leader in a regiment under command by Paul von Lettow-Vorbeck. Stummel was then subordinated to III. Naval Brigade, before being transferred on 30 June 1920, for a few months to the Ships Cadre Detachment of the Baltic Sea as a platoon leader. From January to March 1921, Stummel was a company officer of II. Battalion Ships Cadre Detachment of the Baltic Sea. Stummel was promoted to Oberleutnant zur See on 1 April 1922 and underwent signals training to June 1922. Stummel became a battalion officer in the signals battalion of the naval station in the Baltic Sea, a position he held until 6 May 1923. He was then posted for eight months as radio and watch officer on the cruiser and coastal defense ship , remaining in the position until February 1924. Stummel, who was Maertens chief of staff, was promoted to rear admiral, to take his place. Stummel maintained that the Enigma:

had on the basis of repeated and thorough investigations, proved itself up to the present as unbreakable and military resistant.

Dönitz apparently believed him, as in June he was telling the Japanese ambassador, Hiroshi Ōshima, who was himself one of the main sources of communication intelligence for the allies during the war, that the U-boat losses were due to a new Allied Direction finding system.

Despite the claims, and perhaps nagging doubt that the Enigma machine cipher was insecure, in 1944, Stummel convinced Dönitz to carry the Kriegsmarine basic cryptography principles to its logical conclusion. By subdividing the navies cryptography map into as many Enigma key nets as necessary, Stummel tried to ensure that the number of messages for a specific key was reduced, thereby increase security of own processes. As the volume of traffic increased from the interwar period, when it was one key net, to separate to separate key nets as the message volume increased, to the addition of a U-boat net and many others by 1943, when traffic average 2563 radio messages a day. By then, Stummel decided to give each U-boat its own key.

Individual keys were issued to some U-boat shortly after the Normandy landings on 6 June 1944. They began to be widely used by late 1944 and early 1945 and were carrying all the operational traffic of the Kriegsmarine High Command. In the early months of 1945 Dönitz told Hitler that Allied knowledge of wolfpacks came from radar and espionage. By that time Stummel had been removed from the navy High Command. However, his faith in individual keys was justified, as they were only broken for brief periods.