Last week the National Museum of Computing at Bletchley Park discovered the teleprinter of a Lorenz SZ42 cipher machine for sale as a “telegram machine” on eBay. Museum volunteers went to Southend to inspect it in person. They found it in its original case on the floor of a shed, confirmed it was a Lorenz teleprinter and paid the seller the “Buy it now” price of £9.50 ($14). It is going on display with a Lorenz SZ42 code machine loaned by the Norwegian Armed Forces Museum to tell the full story of how the British broke the Lorenz code.
The Lorenz SZ42 cipher machine was used to transmit the top-secret messages of the German High Command to Army Commands in German-occupied countries. The operator would type the message in plain text on the keyboard of a teleprinter connected to the Lorenz cipher machine which would then convert the message into code. It was in widespread use from 1942 until the end of the war, and with 12 wheels each with a different number of cams, the code it generated was deemed unbreakable.
Andy Clark, chairman of the trustees at The National Museum of Computing, said the Lorenz was stationed in secure locations as “it was far bigger than the famous portable Enigma machine”.
“Everybody knows about Enigma, but the Lorenz machine was used for strategic communications,” said Clark.
“It is so much more complicated than the Enigma machine and, after the war, machines of the same style remained in use.”
Little did the Nazis know the British deciphered the code six months after the first experimental Lorenz SZ40 started sending data in June of 1941. A remarkable feat of reverse engineering by cryptographer Bill Tutte cracked the code in January 1942. Tutte and his team at Bletchley Park figured out the design and function of the machine without ever having seen one. Operator error in a message transmitted from Athens to Vienna on August 30th, 1941, gave the cryptographers a unique opportunity Bletchley to figure out the plain text and the keystream.
Bletchley analysts saw their first Lorenz cipher machine in 1945. By then they had intercepted and read enormously important tactical messages for four years. That’s how the Allies were able to confirm that the Germans had swallowed their bluff that the D-Day landings were happening at Calais. The breaking of Lorenz also played a major role in the construction of Colossus, the first programmable computer. Post Office engineer Tommy Flowers devised Colossus to calculate the positions of the 12 wheels of the Lorenz code machine in hours rather than weeks.
The Lorenz SZ42 encryption machine is extremely rare. Only 200 were built during the war and just four known examples survive. Lorenz teleprinters, on the other hand, were standard production, with a large number of commercial models manufactured. The military-issue teleprinter is much more rare than the commercial models. Bletchley staff first thought it was a standard commercial teleprinter. They only realized it was the rarer military issue, complete with its wartime serial number, swastika accents and a special key for the insignia of the Waffen-SS, when they brought it back to the museum for cleaning and conservation.
The code machine is missing its motor. The museum hopes there’s a Lorenz motor out there in someone else’s shed that would allow them to restore the whole apparatus to working order. If you see something in your attic that looks like a motor in smooth black capsule-like casing with shafts on both sides manufactured by the Lorenz Company at Tempelhof in Berlin, please contact the National Museum of Computing.