What drove the development of Computing in Britain?

Lorenz Machine

Lorenz Machine

We are all aware of the important part computers play in our lives today but they are a relatively new invention. The first use of the word 'computer' goes back to the 1600's but it was then being used to refer to someone's ability to perform calculations. Mechanical devices, usually produced for carrying out limited functions such as numerical calculations (pre-cursors to calculators) or astronomical calculations have been around even longer. In the 1800s Charles Babbage was the first person to think and design a fully programmable device that we would recognise as a computer. However, his device was never built until the late 1980's. However, Babbage ushered in a new wave of designed and built analogue computers.

Alan Turing - a pioneer in computational thought

Lorenz Machine

One of many huts that housed the code breaking activities at Bletchley Park

Alan Turing, an English mathematician, is widely regarded as the father of modern computer science due to his work on algorithms and computation with his 'Turing Machine' in the 1930s. This was the real beginning of the development of electronic digital computers and why he is considered by many as one of the 100 most influential people of the 20th century.

Turing worked at Bletchley Park during the Second World War, the headquarters of the Government Code and Cypher School and now the home of The National Museum of Computing. Britain was struggling in the war against Germany. The British Fleet was being increasingly attacked by the German U-boats and troop movements were pushing the British offensive back. The Germans used two ciphers, or secret codes, to encrypt their communications and stop the British learning of their plans. The machines they used to produce the ciphers were the Enigma and Lorenz machines.

Just before the outbreak of the war an Enigma machine was captured, unknown to the Germans, and this helped Turing design an electromechanical machine, The Bombe, so the British could decode transmissions they intercepted.


The Lorenz cipher machine was used by the German High Command for strategic communications and had never been seen by the British and so decoding it was far more difficult. A mistake in a message transmission by the Germans, using a Lorenz cipher machine, was intercepted and after much effort the way in which the Lorenz cipher worked was discovered. Decrypting more Lorenz cipher messages by hand was now possible but terribly slow and so Tommy Flowers, designed the Colossus machine – a semi programmable digital computer to speed up the process. This became operational in 1943. Colossus is now viewed to have offered a significant contribution to the Allied powers in helping to beat Nazi Germany at the end of World War 2.

The work on computers and code-breaking was so secret at Bletchley Park that the government kept the existence of the Colossus and the Bletchley Park cryptographers and engineers top secret.

Tommy Flowers was a name unknown to most in the computing science field and until the 1970s, when the British government finally declassified documents and blueprints about the wartime work at Bletchley Park, many...were astounded. It is only now that more information is known about it that people realise how important it was in the evolution of computing, not to mention it's importance in the victory over Nazi Germany. Many of the engineers involved in the construction of Colossus 1 and 2 went on to be pioneers in the field, many adapting and refining ideas used in that first digital programmable and electronic machine.


Colossus used the latest technology of the day, vacuum tubes (a device to control electric current), thyratrons (high energy electrical switch) and photomultipliers (extremely sensitive light detector) to allow it to read a paper tape fed into the machine (with the intercepted transmission on it) and applied a programmable logical function to every character, counting how often this function returned "true". This programmability made Colossus the first programmable electronic digital machine (although limited by modern standards).

  • Colossus had no internally stored programs. Plugs and switches were set manually by an operator to alter the wiring to set it up for a new task.

  • It had no internal memory - it read and re-read the transmission by looping the input tape over and over again removing the need to hold it in memory as a modern computer might do. It could read 5000 characters per second using it's optical paper tape reader.

  • Colossus was designed for a specific cryptanalytic task involving counting and Boolean operations. It was not a general-purpose machine and although attempts were made after the war to adapt some Colossus machines to other uses these were limited in success.


Once a message in cipher text was read the machine then went logically through different 'wheel' positions to see if it could identify patterns and predict how the message had been encrypted to then help humans reverse the operation and read the original message. It could take several hours, even reading at 5000 characters per second and being capable of carrying out 5 simultaneous tests, each containing up to 100 Boolean calculations. However, after a few hours it would have helped in breaking the meaning of the cipher text, a task which by hand alone would have taken several weeks.

  • Colossus Introduction

    Running time: 01:27

  • Colossus Input

    Running time: 00:41

  • Colossus Programming part 1

    Running time: 00:33

  • Colossus Programming part 2

    Running time: 01:15

Teacher Notes