Who invented it? Certainly not “the Swiss”. But was it “the Germans”, more precisely: a German named Fritz Menzer, or “the Swedes”, essentially the Stockholm cryptographer Boris Hagelin? This is not a secondary question, because it is about the “Hitlermühle”, technically speaking the key device 41. A cipher machine that would have eliminated a significant advantage of the British and Americans in one fell swoop. Because since 1941 the Allies could read the radio traffic of the Wehrmacht (with the exception of the U-boats), which was encrypted with the older Enigma machine, almost in real time and since mid-March 1943 practically always.
The German Museum in Munich has its own department for cipher machines, which includes two of the extremely rare cipher devices 41 in addition to a few Enigmas. On November 8, 2022, the house, one of the largest and most frequented museums in Germany in terms of area and audience, took a clear position in the form of a seven-part film on the museum app: According to this, Fritz Menzer is said to have been the brain behind the “Hitlermühle”.
In order to better understand the contrast, one must delve deeply into one of the most secret topics of the 20th century – so secret that even the greatest success of intelligence work against the Nazi dictatorship was only published almost 30 years after the end of the war: the victory of the British ( with Polish, French and American help) via the Enigma.
Fritz Menzer, born in 1908 on the edge of the Saxon Ore Mountains, had enlisted in the Reichswehr in 1926 as a trained toolmaker. The period of service for non-commissioned officers was twelve years. In his otherwise unremarkable service in 1935, it was noticed that he had an aptitude for cryptography. So for the art of encrypting messages in such a way that the intended recipient can read them but no one else. Before the invention of electronic computing devices, mechanical or electromechanical devices were used for this.
But even if the opponent (a hostile state or just a competing company) could obtain such a device, nothing was lost. Because encryption methods from the first half of the 20th century had, greatly simplified, three elements: first, the device itself; second, a key book that was always kept separately, often printed with water-soluble ink on particularly flammable paper, so that it was easy to destroy; thirdly, rules that only the respective cipher specialists knew and which were not recorded in writing. Even if two of these three elements fell into the hands of an adversary, the encryption was still secure.
Unless, yes, unless your own device had fundamental defects. Exactly that was the case with the Enigma, a development of the Berlin “Ciphering Machine Society”, a private company. Because this device was considered unbreakable from its introduction in 1924, the Reichswehr and, from 1935, the Wehrmacht used it as the standard encryption system.
The Enigma’s shortcomings were simple: it never encoded a letter as itself, and at the same setting it encoded in mirror image – a “V” for example then always became an “A”, but also an “A” became a “V”. These two weaknesses became the gateway with which Polish cryptologists first found “access” to Enigma-encrypted messages using incredibly complicated mathematical processes. They passed their knowledge to the French and British in 1939, who continued to refine it.
From 1940 onwards, specialists working with the brilliant Alan Turing in Bletchley Park north-west of London regularly read the Enigma messages from the German Air Force and the Army. The Enigma-based but more complicated encryption of the German submarines, which were particularly dangerous for Great Britain, was cracked for the first time in the spring of 1941. But due to the introduction of a new variant of the machine, a blackout began in February 1942, which was only overcome after ten months: from the beginning of 1943, the Western Allies read almost all German communications.
Fritz Menzer had completed his service in 1938, but remained as a civil servant in the encryption department of the Wehrmacht High Command, to which the former Reichswehr Ministry had been reorganized and for which he had worked since 1935. From 1940 he held the rank of senior government inspector, i.e. at the second level of the higher (but not higher) civil service career, corresponding to a lieutenant in the Wehrmacht, and worked on improvements to the German encryption system. According to a US Army report dated May 1, 1946, Menzer worked as a “Senior Inspector” with the “development and production of encryption methods for ministries, industry and the Reich Security Main Office as well as the development of decryption aids for agents”.
According to the cryptography expert and technology historian Michael Prose, Menzer was “not a scientific cryptologist, but probably dealt with technical requirements for cipher machines, especially with the purely mechanical Hagelin machines”. Its namesake was a Swedish cryptologist who had filed a patent for a cipher machine in 1928. This avoided the two structural flaws of the Enigma – and was used in very different variants on both sides during the Second World War: as the M-209 en masse by the US armed forces and as the C-38 by the Italian Navy.
According to the research results of the Deutsches Museum, it was Menzer who had the basic idea for a new and secure mechanical encryption machine based on the Hagelin method. Prose, on the other hand, sees him as just a “technical clerk” who formulated the specifications according to which the office machine engineers at Wanderer-Werke in Saxony developed the Key Device 41. In any case, the cryptanalysts at Blechtley Park did not succeed in finding a decryption method for this machine until 1945.
From a British point of view, however, that did not matter, because only about 1,500 units of the Device 41 were made by the end of the war because this machine was too large and weighed up to 15 kilos – almost half the weight of the Enigma. The German Navy (the three branches of service were responsible for the decision on encryption methods, not the OKW encryption department) had also demanded that a new device had to be compatible with the Enigma. A serious disadvantage, because it meant that their weaknesses had to be adopted as well.
The attempt to use a smaller mechanical encryption machine, the key device 39, which had already been developed in 1939, heavily modified according to Menzer’s specifications, at least in the army and air force, failed due to a lack of resources in the Third Reich. Especially since the Nazi leadership still wrongly considered the Enigma to be “safe”.
Whether Fritz Menzer was actually the “inventor” of the key device 41 or whether he only made specifications as a clerk, which were implemented by cryptographic engineers, cannot yet be answered with certainty. However, something speaks for the interpretation of the Deutsches Museum: After his interrogations by the US Army, he was also interrogated by the Soviets, then fled to West Berlin and finally worked as head of the punch card office of the Federal Debt Administration in Bad Homburg.
However, he still received the Federal Cross of Merit in 1973 – for what purpose is unknown. That at least allows the assumption that he worked for the BND or another intelligence service. Fritz Menzer died in 2005 at the age of 97. Apparently he never spoke about his work, not even to his children.
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