SafekipediaColossus computer
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Colossus was a set of computers built by British codebreakers from 1943 to 1945. These machines helped solve very hard codes used by German leaders during World War II. Colossus used many small parts called thermionic valves (vacuum tubes) to do logical and counting tasks, which was an important step in the history of computing.
The Colossus computers were designed by engineer Tommy Flowers, working with mathematician Max Newman at Bletchley Park, a secret center for codebreaking. Although famous scientist Alan Turing helped with codebreaking methods, he did not design Colossus; his work focused on a different machine called the Bombe used against another German code called Enigma.
The first Colossus machine, called Colossus Mark 1, began working in December 1943 and was used at Bletchley Park by early 1944. A faster version, the Colossus Mark 2, was ready by June 1944, just in time to help with the important Normandy landings on D-Day. By the end of the war, ten Colossus machines were in use, giving the Allies useful information from German messages.
For many years, the existence of Colossus was kept a secret. The machines were mostly taken apart, and details about them were not told until the 1970s. In 2008, a working reconstruction of a Colossus Mark 2 was finished and is now on display at The National Museum of Computing at Bletchley Park.
Purpose and origins
See also: Cryptanalysis of the Lorenz cipher
The Colossus computers helped to read secret radio teleprinter messages. These messages were hidden using a secret method called "Fish" and the machine that hid them was called "Tunny".
British experts learned how the German machine worked and made their own called "British Tunny". They found it used twelve wheels and a special way to mix messages. In 1941, a mistake by German workers helped the British learn more about the machine.
To read the secret messages, two things needed to be done. The first was to find the patterns of the wheels, and the second was to find where the wheels started for each message. Colossus was made to help with the second job by comparing messages and counting certain patterns.
Decryption processes
The Colossus computer helped British codebreakers read secret messages during World War II. By studying patterns in the messages, they could find important starting points for the machines that made the codes. This made it easier to understand the messages.
With these starting points, the team at Bletchley Park used other ways to fully decode the messages. Later, Colossus also helped find starting points for more parts of the coding machine.
| P {\displaystyle P} | plaintext |
| K {\displaystyle K} | key – the sequence of characters used in binary XOR with the plaintext to give the ciphertext |
| χ {\displaystyle \chi } | chi component of key |
| ψ {\displaystyle \psi } | psi component of key |
| ψ ′ {\displaystyle \psi '} | extended psi – the actual sequence of characters added by the psi wheels, including those when they do not advance |
| Z {\displaystyle Z} | ciphertext |
| D {\displaystyle D} | de-chi—the ciphertext with the chi component of the key removed |
| Δ {\displaystyle \Delta } | any of the above XOR'ed with its successor character or bit |
| ⊕ {\displaystyle \oplus } | the XOR operation |
| ∙ {\displaystyle \bullet } | Bletchley Park shorthand for telegraphy code space (zero) |
| x {\displaystyle \mathbf {x} } | Bletchley Park shorthand for telegraphy code mark (one) |
Design and construction
Colossus was built for the "Newmanry", a team led by mathematician Max Newman. They worked on breaking a secret code machine called the Lorenz SZ40/42 on-line teleprinter cipher machine, known as Tunny. The idea for Colossus came from an earlier machine called the "Heath Robinson". This machine showed that machines could help with code breaking, but it was slow and had trouble keeping tapes in sync.
Tommy Flowers MBE, an engineer, designed Colossus. He believed that using electronic parts could fix the problems of the Heath Robinson machine. His first model, called Mark 1 Colossus, used 1,600 electronic parts named thermionic valves (or vacuum tubes). It worked well in tests and was moved to Bletchley Park. There, it began decoding messages in February 1944. Later, an improved version called Mark 2 Colossus was created. This version was faster and easier to use, with 2,400 valves. The first Mark 2 was ready just in time to help the Allies on D-Day. By the end of the war, ten Colossus machines were used at Bletchley Park to help break coded messages.
Operation
The Newmanry had cryptanalysts, operators from the Women's Royal Naval Service (WRNS) – called "Wrens" – and engineers for fixing the machine. By the end of the war, 272 Wrens and 27 men worked there.
To use Colossus for a new message, the Wrens would make a paper tape loop by sticking the ends together. They would punch special holes to show where the message began and ended. The operator would then put the tape through the machine and adjust it before starting, following directions from a cryptanalyst.
Programming
Colossus was not a stored-program computer. Its work was guided by switches and wires on a special panel. Each part of the machine did particular jobs and could count certain results.
People could pick different settings, which let the machine try many ways to study secret German messages. This helped solve very hard puzzles during World War II.
Influence and fate
The Colossus computers were special machines made to help solve secret codes during World War II. They were the first electronic digital machines that could be programmed, but they were only used for specific tasks.
After the war, most of the Colossus machines were taken apart. Their secret was kept for many years. Only a few parts were kept for research. The full story of Colossus was not known until much later. Some people who worked on Colossus later helped develop new computers, but the machine itself did not directly shape modern computing because its existence was kept secret.
Reconstruction
A team led by Tony Sale built a working version of the Colossus Mark 2 computer between 1993 and 2008. They used old engineers’ notes and materials from the United States to rebuild it. You can see the reconstruction at The National Museum of Computing in Bletchley Park, Milton Keynes, Buckinghamshire.
In November 2007, a special event called the Cipher Challenge tested the rebuilt Colossus. Radio amateurs around the world tried to decode secret messages sent from a museum in Germany. A radio amateur named Joachim Schüth won the challenge using a modern laptop. This event showed how well the reconstruction worked and honored the people who built the original Colossus during World War II.
Other meanings
See also: List of fictional computers
The name Colossus was used for a pretend computer in the 1970 movie Colossus: The Forbin Project, based on a book by D. F. Jones. This happened by chance, because the movie was made before people knew about the real Colossus computer.
The name also appears in Neal Stephenson’s book Cryptonomicon (1999), which tells stories about the history of Turing and Bletchley Park. There is also a Colossus (supercomputer), which is known as the world's largest AI supercomputer.
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