The Colossus vacuum tube computer

November 24, 2016 // By Steve Taranovich
Steve Taranovich discusses the role of one of the first computers in breaking a coding system that was even stronger than the Enigma system.

I have always been interested in electronics engineering ingenuity used to solve “impossible” problems. One such problem was the task of deciphering the German Army’s most secret transmissions during WWII via a German teletype machine that was codenamed Tunny (that’s what the British called tuna). The SZ40 was one such cipher machine used as a teleprinter attachment.

The German SZ40 cipher machine (Image courtesy of Stanford University, Reference 2)

Due to a keying mistake made by a German operator on an SZ40 in 1941, the details of which the British have never revealed, the cryptographers were able to determine that the German machine had wheels with variable pin settings, plus that there were 12 of these wheels, the sizes of the wheels (which were in essence the number of variable pin settings on each) were 23, 26, 29, 31, and a continued progression. They also were able to determine that the rotors moved in relation to one another as a message was enciphered. This was the first of two things that helped change the course of the war.

The second one was that in order to decipher the SZ40, they needed a very fast rate of operation in a British cryptanalysis machine which was not presently available in the mechanical devices used in order to determine the patterns around the circumferences of all 12 wheels in the SZ40 at a particular point in time since the Germans were regularly changing the pin-setting patterns. After that, they would need to figure out the settings of the wheels at the beginning of the message. Maxwell Newman, a 45 year-old mathematician from the University of Cambridge, was chosen to head up the effort to break the German teletype traffic.

That same year, 1943, work was in progress on Colossus, a high-speed programmable machine. Thomas H. Flowers was the chief engineer on the Colossus project, who had been looking into how he could use