Having deciphered its underlying principle in spring 1940, they were able to transform encrypted messages into plain text at the flick of a switch from 1941.
How do you regain the advantage? Build a much better coding machine of course. In 1941 the Wanderer Werke in Chemnitz was commissioned to develop a new, improved version.
New and improved
Based on significant input from the cryptologist Fritz Menzer (1908-2005), the purely mechanical Schlüsselgerät 41 (SG-41) was now modelled on a fundamental principle developed by the Swedish cryptologist Boris Hagelin (1882-1983), albeit with important modifications.
Unlike the Enigma, which used lamps for the letters, new features included working with two reels of paper. The encryption process involved turning the drum through 360 degrees with the attached crank handle to rotate six cipher wheels, rather than the previous three.
The SG-41 was nicknamed ‘HitlerMill’ because of the crank that had to be turned for operation.
The world’s largest science and technology museum, the Deutsches Museum in Munich, received one recently that had been excavated, heavily corroded and clearly not functional, as an archaeological find.
However, at Hermann Historica’s auction also in Munich, on May 20-24, what the saleroom calls a “perfectly preserved specimen” of a Schlüsselgerät 41 is on offer with a starting estimate of €75,000.
The Allies were fortunate that it was not deployed on a large scale– of the 11,000 devices ordered, only about 500 units were shipped to the Abwehr, or military intelligence service, and another 1000 to the weather service, and it was not introduced anyway until late 1944.
Many were destroyed by the Germans towards the end of the war so surviving examples are rare.
Hermann Historica notes: “Even the experts in England failed to reconstruct – and thus decipher – the SG-41 by the end of the war.”