One of Turing’s mentors in Princeton was John von Neumann, the brilliant physicist and mathematician who had fled his native Hungary and was at the Institute for Advanced Study, which for the time being was located in the building that housed the university’s Mathematics Department. In the spring of 1938, as Turing was finishing his doctoral thesis, von Neumann offered him a job as his assistant. With the war clouds gathering in Europe, the offer was tempting, but it also felt vaguely unpatriotic. Turing decided to return to his fellowship at Cambridge and shortly thereafter joined the British effort to crack the German military codes.

His Majesty’s Government Code and Cypher School was, at the time, located in London and staffed mainly by literary scholars, such as Dillwyn “Dilly” Knox, a classics professor from Cambridge, and Oliver Strachey, a dilettante socialite who played piano and occasionally wrote about India. There were no mathematicians among the eighty staffers until the fall of 1938, when Turing went there. But the following summer, as Britain prepared for war, the department began actively hiring mathematicians, at one point using a contest that involved solving the Daily Telegraph crossword puzzle as a recruitment tool, and it relocated to the drab redbrick town of Bletchley, whose main distinction was being at the juncture where the railway line between Oxford and Cambridge intersected with the one from London to Birmingham. A team from the British intelligence service, posing as “Captain Ridley’s shooting party,” visited the Bletchley Park manor house, a Victorian Gothic monstrosity that its owner wanted to demolish, and discreetly bought it. The code breakers were located in the cottages, stables, and some prefabricated huts that were erected on the grounds.⁷⁴

Turing was assigned to a team working in Hut 8 that was trying to break the German Enigma code, which was generated by a portable machine with mechanical rotors and electrical circuits. It encrypted military messages by using a cipher that, after every keystroke, changed the formula for substituting letters. That made it so tough to decipher that the British despaired of ever doing so. A break came when Polish intelligence officers created a machine based on a captured German coder that was able to crack some of the Enigma codes. By the time the Poles showed the British their machine, however, it had been rendered ineffective because the Germans had added two more rotors and two more plugboard connections to their Enigma machines.

Turing and his team went to work creating a more sophisticated machine, dubbed “the bombe,” that could decipher the improved Enigma messages—in particular, naval orders that would reveal the deployment of U-boats that were decimating British supply convoys. The bombe exploited a variety of subtle weaknesses in the coding, including the fact that no letter could be enciphered as itself and that there were certain phrases the Germans used repeatedly. By August 1940 Turing’s team had two operating bombes, which were able to break 178 coded messages; by the end of the war they had built close to two hundred.

The Turing-designed bombe was not a notable advance in computer technology. It was an electromechanical device with relay switches and rotors rather than vacuum tubes and electronic circuits. But a subsequent machine produced at Bletchley Park, and Colossus, was a major milestone.

The need for Colossus arose when the Germans started coding important messages, such as orders from Hitler and his high command, with an electronic digital machine that used a binary system and twelve code wheels of unequal size. The electromechanical bombes designed by Turing were powerless to break it. It required an attack using lightning-quick electronic circuits.

The team in charge, based in Hut 11, was known as the Newmanry after its leader, Max Newman, the Cambridge math don who had introduced Turing to Hilbert’s problems almost a decade earlier. Newman’s engineering partner was the electronics wizard Tommy Flowers, a pioneer of vacuum tubes, who worked at the Post Office Research Station at Dollis Hill, a London suburb.

Turing was not part of Newman’s team, but he did come up with a statistical approach, dubbed “Turingery,” that detected any departures from a uniform distribution of characters in a stream of ciphered text. A machine was built that could scan two loops of punched paper tapes, using photoelectric heads, in order to compare all possible permutations of the two sequences. The machine was dubbed the “Heath Robinson,” after a British cartoonist who specialized, as did Rube Goldberg in America, in drawing absurdly complex mechanical contraptions.

For almost a decade Flowers had been fascinated by electronic circuits made with vacuum tubes, which he and other Brits called “valves.” As an engineer with the Post Office’s telephone division, he had created in 1934 an experimental system that used more than three thousand tubes to control connections among a thousand phone lines. He also pioneered the use of vacuum tubes for data storage. Turing enlisted Flowers to help on the bombe machines and then introduced him to Newman.

Flowers realized that the only way to analyze the German encrypted streams quickly enough was to store at least one of them into the internal electronic memory of a machine rather than trying to compare two punched paper tapes. This would require 1,500 vacuum tubes. At first the Bletchley Park managers were skeptical, but Flowers pushed ahead, and by December 1943—after only eleven months—he produced the first Colossus machine. An even bigger version, using 2,400 vacuum tubes, was ready by June 1, 1944. Its first decoded intercepts supported other sources informing General Dwight Eisenhower, who was about to launch the D-Day invasion, that Hitler was not ordering extra troops to Normandy. Within a year, eight more Colossus machines were produced.

This meant that well before ENIAC, which did not become operational until November 1945, the British code breakers had built a fully electronic and digital (indeed binary) computer. The second version, in June 1944, was even capable of some conditional branching. But unlike ENIAC, which had ten times the number of tubes, Colossus was a special-purpose machine geared for code breaking, not a general-purpose computer. With its limited programmability, it could not be instructed to perform all computational tasks, the way that (in theory) ENIAC could.

SO, WHO INVENTED THE COMPUTER?

In assessing how to apportion credit for creating the computer, it’s useful to begin by specifying which attributes define the essence of a computer. In the most general sense, the definition of a computer could encompass everything from an abacus to an iPhone. But in chronicling the birth of the Digital Revolution, it makes sense to follow the accepted definitions of what, in modern usage, constitutes a computer. Here are a few:

“A programmable usually electronic device that can store, retrieve, and process data.” (Merriam-Webster Dictionary)

“An electronic device which is capable of receiving information (data) in a particular form and of performing a sequence of operations in accordance with a predetermined but variable set of procedural instructions (program) to produce a result.” (Oxford English Dictionary)

“A general purpose device that can be programmed to carry out a set of arithmetic or logical operations automatically.” (Wikipedia, 2014)

So the ideal computer is a machine that is electronic, general purpose, and programmable. What, then, best qualifies as the first?

George Stibitz’s Model K, begun on his kitchen table in November 1937, led to a full-scale model at Bell Labs in January 1940. It was a binary computer and the first such device to be used remotely. But it used electromechanical relays and was thus not fully electronic. It was also a special-purpose computer and not programmable.