See New Pictures of WWII Code-Breaking Computer Colossus

Recently released picture of the Colossus. (source: GCHQ)

Britain’s Government Communications Headquarters has released new pictures of the Colossus, a revolutionary computer that deciphered Nazi codes during World War Two. Check them out here!

The Colossus prototype was built at the Post Office Research Laboratories by Thomas Flowers, a telephone engineer working for Bletchley Park, the nerve center of the Allies’ code-breaking work during the war. It automated the decryption of the telegrams sent with the Lorenz SZ42, used by Nazi high officials, gathering intelligence that saved innumerable lives and helped shorten the war. The Colossus’ use at Bletchley was a state secret, only officially acknowledged in 2000 by the GCHQ. With the release of these pictures, we know just a little bit more about one of the most important computers ever built.

The Lorenz SZ42 cipher machine encrypted its message by including randomly generated characters intermixed with the message’s characters. This made the messages impossible to break, but only if each message used a different preset of Lorenz’s twelve code wheels. If two messages with the same preset (called a depth) were intercepted, the obscuring characters could be identified and the code broken. The only problem was that all Lorenz operators knew to use a different preset for each message.

Code Breakers at work in Bletchley Park's Hut 6. (source: Encyclopædia Britannica)

The Nazi’s fatal mistake came on August 30, 1941. A message from occupied Athens to Vienna failed and was sent again, using the same preset. On the second attempt, the machine operator wrote a condensed version of the previous message, producing a depth. Both messages were recorded by a radio intercept station at Knockholt in southern England and were quickly passed on to Bletchley Park. Once there, Brigadier John Tiltman was able to identify the obscuring pattern used in both messages. With this, codebreaker William Tutte and his team reverse-engineered Lorenz’s encoding pattern, breaking the code.

Breaking Lorenz codes by hand could take weeks, but with Colossus, the process was automated. The computer’s internal memory was maintained by 1,500 vacuum tubes and used electronic ring circuits to synchronize the machine’s two data inputs: the broken wheel pattern codes and the raw encrypted messages. Now codes could be broken in mere hours, providing invaluable intelligence, including for the D-Day invasion. Work from Colossus also helped spawn Alan Turing’s bombe, used to break the Enigma code, another breakthrough both in the fight against the Nazis and in computer technology.

Want to read about another revolutionary computer? Check out our article on the Cray-1, or browse our collection of Cray-1 computer chips!

Read More!

Rojas R, Hashagen U. The First Computers: History and Architectures. MIT Press; 2002.

Shipley H. Turing: Colossus Computer Revisited. Nature (London). 2012;483(7389):275-275. doi:10.1038/483275b