The Science Museum’s Difference Engine No. 2, built from Babbage’s design

The first design for a computer was, of course, a mechanical device with gears and levers designed by the British mathematician Charles Babbage. He first wrote down the idea in a letter to Sir Humphrey Davy in 1822. His design could not be manufactured at the time (machining tolerances were not sufficiently advanced) but in 1991 a version was manufactured and was shown to work at the Science Museum, London. Babbage envisaged using a mechanical computer to calculate the odds on a horse race, since he was an inveterate gambler.

Zuse Z1 replica in the German Museum of Technology in Berlin

Germany, 1938

The first person actually to construct an electromechanical computer was a German aircraft technician and amateur enthusiast, Konrad Zuse. He used punched paper tape to input data and developed the first programming language, Plankalkül (plan calculus). His first machine, the Z1, was able to use binary floating point numbers, which allows for large calculations, and a form of programming based on the work on the Victorian English mathematician George Boole. Boole derived the form of analysis that combines terms (using ‘and’) or splits them into alternatives (‘or’) and Boolean logic, as we now call it, is essential in writing software. This early computer had no relays and a single electrical unit to give a clock speed of 1Hz. The Z1 could be programmed using punched tape and a tape reader. Zuse built it with his own (and his family’s) money between 1936 and 1938, using part of the family living-room as his laboratory. This pioneering computer embodied most of the components we would recognize in a present-day machine, including a control unit and simple computer memory. He went on later to construct more advanced prototypes and hoped to make them commercially available. However, although he made several attempts to interest the German military in the possibilities offered by his computer, no-one there was interested. All his machines, and the documentation, were destroyed during the Allied bombing raids on Berlin in December 1943.

Colossus Mark 2

England, 1944

The first programmable electronic computer was named Colossus, and was produced specifically to crack the Lorenz codes used by the German High Command, since these codes were more complex than those generated by Enigma. Colossus was designed and built by a team led by Harold Thomas Flowers who began working on the idea in the late 1930s. As a young engineer, Tommy Flowers had the idea of using thermionic radio valves, or vacuum tubes, as programmable switches. He fed data in using punched tape, like a ticker-tape machine. His original idea was to automate the British telephone exchanges, but as the war took hold news reached him of the need to decode German messages that were being intercepted by the intelligence service as part of the Ultra project. Tommy Flowers began work in 1941 and took just six months to demonstrate a prototype machine, and – unlike Zuse – he found the British authorities were becoming interested in what his computer could do.

In February 1943 construction work on the revolutionary computer began at the Post Office Research Station in Dollis Hill, North-West London. The computer was running successfully by December that same year, so it was disassembled and driven to Bletchley Park on 18 January 1944. It was fitted together again and worked perfectly, and was given its first message to decode on 5 February 1944. This Mark 1 Colossus was such a success that a further nine of the giant computers were ordered. The design and specifications were improved, and in June 1944 the Mark 2 went into full production. Colossus Mark 1 contained an astonishing 1,500 electronic tubes developed for radios, whilst the Mark 2 was fitted with 2,400 of these valves making it both simpler to use and five times faster. These Colossus computers could process nearly 10,000 characters per second, but the paper tape soon became shredded. The punched paper tape could pass safely through the readers at a maximum speed of 27.3mph (12.2m/s) so they settled on 5,000 characters per second as the optimum rate of operation. Trials were also held where two Colossus computers were used simultaneously on the same problem, thus proving the value of parallel computing.

It was the use of the Colossus machines by the War Department in London that allowed the British to considerably reduce the ability of German Admiral Karl Dönitz to make unexpected raids upon the convoys crossing the North Atlantic, and thousands of lives must have been saved. These Allied victories turned the course of the war.

After the war

The Americans stationed at Bletchley Park were highly impressed, and encouraged John Mauchly and J. Presper Eckert to press ahead with the design of a more advanced version at the Moore School of Electrical Engineering of the University of Pennsylvania. Their design and development was code named Project PX and their prototype machine, ENIAC, was unveiled after World War II was over, on 14 February 1946. It had cost some $500,000 to build, worth $6 million today, a huge sum of money for such a project. This state-of-the-art computer was intended to make artillery calculations, but was soon being utilized for work on the development of the first hydrogen bomb.

Meanwhile, in Britain, even the very existence of Colossus was covered by the Official Secrets Act and it all remained a state secret well into the 1970s. The British authorities have always been sensitive about classified information, and the staff at Bletchley Park refused to talk about their work even into the 1990s. Although all of the ten Colossus computers survived into the 1980s, they were broken up and their records destroyed. The teams remained silent.

Reclaiming history

The historical importance of the early Zuse computers became increasingly apparent in the post-war years, and in 1986 Konrad Zuse resolved to rebuild his original Z1 computer. It remains an important historical device for it embodies all the essential components we recognize in present-day computers. The task took him three years, and it was shipped to the Deutsches Technik Museum in Berlin-Kreuzberg where it is on display, in full working order, to this day.

Turing’s name has been widely celebrated in the decades that have elapsed since his untimely death. There are institutes, buildings, prizes, award schemes and mathematical principles all devoted to his name. Breaking the Code was a play about Turing’s life by Hugh Whitemore that was first performed in 1986, and was a success both in London’s West End and on Broadway, where it received three Tony Award nominations. Another successful drama about Turing’s life was screened by BBC television in 1996, and Turing’s story featured in a television documentary, Dangerous Knowledge, in 2008. There are commemorative plaques at his birthplace in London and his former home in Wilmslow, Cheshire, and in March 2000 a set of stamps with his portrait was issued in the Caribbean. In 2001 a statue of Turing was unveiled in Manchester and three years later a bronze statue by John Mills was unveiled at the University of Surrey, Guildford, to mark the 50th anniversary of his suicide. Another statue was unveiled in 2007 at Bletchley Park. The costs were paid by Sidney Frank, an American philanthropist.

By 1994 it was realized in Britain what a priceless piece of scientific history had been lost by the destruction of the Colossus machines, so the (by now) Sir Harold Thomas Flowers with a team of fellow-enthusiasts unearthed the original drawings for the prototypes and discovered that large parts of the computers had been hidden away by enthusiasts from Bletchley Park. They set to work to rebuild a working Colossus computer, and now that Bletchley Park has become a museum, the computer is on permanent display there, a testimony to the vital role it played in the Allied victory.

And what of the Bomba Kryptologiczna, the all-important Bombe? The remaining components were found at Bletchley and a replica was reconstructed by a team of enthusiasts led by John Harper. This complete and working replica was built at the Bletchley Park museum and was officially switched on by the Duke of Kent, patron of the British Computer Society on 17 July 2008.

When the 50th anniversary of the commissioning of ENIAC loomed in 1996, the University of Pennsylvania and the Smithsonian Institution in Washington DC marked the event with special publications and a huge exhibition involving senior American statesmen. Although ENIAC was designed to be physically rewired to change programming, it remains an inspiring step in the slow but steady progress of computers from Charles Babbage’s imagined machine, to the massive mainframe computers of the present day.


In today’s world, computers are everywhere. We need to recognize that – although the components were available – it took the urgency of war and the need to defeat a highly organized foe that gave the impetus to the design of Colossus and ENIAC. When you contemplate your desktop computer, just reflect: it would certainly have arisen anyway in the fullness of time – but, as it is, even your computer is a legacy of the secret science of World War II. Be cured by antibiotics; write with a ballpoint pen; travel in a jet plane; watch space rockets on television … and just reflect that it was World War II that brought them to reality. In our modern era, everything takes so much time to change and bureaucracy weighs us down. It was very different then, when survival depended on science and time was of the essence. In my view, we could usefully embrace some of those enthusiasms in facing our present-day problems, which (like global pollution and climate change, starvation and water shortage, political expediency and scientific illiteracy) affect everyone in the world. If ever we needed to learn the lessons of that wartime sense of dynamism and purpose, it is now.