1943

Colossus

Thomas Harold Flowers (1905–1998), Sidney Broadhurst (1893–1969), W. T. Tutte (1917–2002)

Colossus was the first electronic digital computing machine, designed and successfully used during World War II by the United Kingdom to crack the German High Command military codes. “Electronic” means that it was built with tubes, which made Colossus run more than 500 times faster than the relay-based computing machines of the day. It was also the first computer to be manufactured in quantity.

A total of 10 “Colossi” were clandestinely built at Bletchley Park, Britain’s ultra-secret World War II cryptanalytic center, between 1943 and 1945 to crack the wireless telegraph signals encrypted with a special system developed by C. Lorenz AG, a German electronics firm. After the war the Colossi were destroyed or dismantled for their parts to protect the secret of the United Kingdom’s cryptanalytic prowess.

Colossus was far more sophisticated than the electromechanical Bombe machines that Alan Turing designed to crack the simpler Enigma cipher used by the Germans for battlefield encryption. Whereas Enigma used between three and eight encrypting rotors to scramble characters, the Lorenz system involved 12 wheels, with each wheel adding more mathematical complexity, and thus required a cipher-cracking machine with considerably more speed and agility.

Electronic tubes provided Colossus with the speed that it required. But that speed meant that Colossus needed a similarly fast input system. It used punched paper tape running at 5,000 characters per second, the tape itself moving at 27 miles per hour. Considerable engineering kept the tape properly tensioned, preventing rips and tears.

The agility was provided by a cryptanalysis technique designed by Alan Turing called Turingery, which inferred the cryptographic pattern of each Lorenz cipher wheel, and a second algorithm. The second algorithm, designed by British mathematician W. T. Tutte, determined the starting position of the wheels, which the Germans changed for each group of messages. The Colossi themselves were operated by a group of cryptanalysts that included 272 women from the Women’s Royal Naval Service (WRNS) and 27 men.

SEE ALSO Manchester SSEM (1948)

The Colossus computing machine was used to read Nazi codes at Bletchley Park, England, during World War II.