During long stretches of the war against Hitler, German bombs were a part of day-to-day life in British cities. The Führer’s first air campaign against British civilians, known to Britons as the Blitz, lasted from September 1940 to May 1941 and led to the dropping of tens of thousands of tons of explosives across the country. London alone was hit by seventy-one major Luftwaffe raids. The bombers were back over Britain in February through May 1944 with Operation Steinbock, the so-called Baby Blitz. The following month brought the V-1s—winged drone aircraft, of which the Germans launched more than ten thousand across the English Channel. The deep growl of a V-1’s engine in the sky above was unnerving to hear. Yet as long as you could hear that sound, it was said, you had nothing to worry about; what you didn’t want to hear was the engine becoming silent, a signal that the machine was about to dive and detonate its 1,870- pound payload. In September, the V-1s would be joined in the air by the V-2, a supersonic missile developed by a team under the rocket engineer Wernher von Braun. Fired from mobile launchers, more than a thousand V-2s would reach England, around half of them striking London. Over the course of the war, roughly 52,000 people in Britain were killed by bomber raids and another 8,500 by V-1s and V-2s.
In contrast, fifty-five miles to the northeast of London, in rural Buckinghamshire, the town of Bletchley remained outwardly quiet, even serene. A visitor to its center of activity, an estate known as Bletchley Park, would have found an unprepossessing Victorian-era mansion, a patchwork of architectural styles that appeared to have been tossed together to suit the eccentric whims of a rich former owner—which was, in fact, the case. Near the mansion on the estate’s fifty-eight acres was a lake with ducks and geese. Herds of deer roamed the grounds.
Also sharing the grounds were two dozen or so low buildings. Some were long wooden huts with whitewashed exteriors, several of them enclosed by five-foot blast walls for protection against bombings. The blast walls were unnecessary, as it turned out, because the Germans never learned of the work taking place within: Bletchley Park was the home of the British signals intelligence agency, which had the cover name of Government Code and Cypher School, or GC&CS for short. Its main task was reading intercepted radio messages of the Third Reich’s military, messages shrouded with advanced encryption methods that the Nazis believed to be, for all practical purposes, impenetrable.
Intelligence about an opponent’s capabilities and intentions has always been central to the waging of war—and cryptography, or decoding, has long been central to intelligence.* But World War II was a cryptographic war like none before it. Hitler’s lightning warfare tactics and his reliance on U-boats meant that his far-flung forces had to use radio to receive their orders and report back. Accordingly, German engineers created machines with advanced encryption technology to safeguard those radio messages from prying enemy ears.
It is widely known that around a third of the way through the war, Bletchley Park unlocked the secrets of one of those creations, the Enigma family of encoding machines. In Hut 8, a team led by British chess champion Hugh Alexander and a twenty-seven-year-old Cambridge-trained mathematician, Alan Turing, successfully attacked the version of Enigma used by the Kriegsmarine, the German navy, saving Britain from the U-boat menace during the Battle of the Atlantic. Their work enabled the Allies to lift the grip of the U-boats that had come close to strangling Britain by cutting off the flow of its supplies. Bletchley Park was able to read naval Enigma traffic temporarily in 1941 and permanently starting in late 1942; the victory was made possible by a mechanical device, principally of Turing’s invention, known as the Bombe, which mimicked the operation of a series of Enigma machines lashed together. The attack on Enigma has been documented and dramatized (sometimes quite fancifully) over the years in books, plays, the 2001 film Enigma, and the 2014 film The Imitation Game.
What is little known is the story that came next—little known because postwar security restrictions kept it hidden for decades, with major parts of it remaining classified until the twenty-first century. The conquest of Enigma was only a warm-up. A different section of Bletchley Park, known as the Newmanry, would become the site of the greatest decryption achievements of the war and the launch of the digital age.
Behind that success were the contents of two low buildings, newer and larger than the huts, made of brick, concrete, and steel. Known as Block F and Block H, the structures contained one of the Allies’ most guarded secrets, second perhaps only to the Manhattan Project: messages between Hitler’s headquarters staff and his generals in the field were being cracked by a new kind of technology—digital electronic computers. The breakthrough yielded, among other things, intelligence that was essential to the D-Day landing.
At this time, even the word computer itself did not exist in reference to machines and would not for some years; the term was reserved for human beings whose job was to carry out long sequences of calculations by hand. Bletchley Park’s electronic computers were called Colossus (plural, Colossi); they shared the binary logic of modern computers, though they were programmed via a plugboard rather than software stored in memory. The machines were not only the first operational digital electronic computers, they were the first large-scale digital electronic devices of any kind.
By way of contrast, until the advent of Colossus, the state of the art in computational machines had been the Harvard Mark I, which was based not on electronics but on thousands of electromechanical parts like switches and wheels, slow and error-prone. So novel was the digital electronic technology of Colossus that one modern-day software engineer has facetiously suggested it must have been inspired by a lost alien supercomputer.
Where Turing’s Bombe was used against the Enigma, Colossus was used against another, much more complex machine, the crown jewel of German encryption technology. Built by the firm C. Lorenz AG, it was known to the Germans as the Lorenz SZ series—for Schlüssel-Zusatz, or “cipher attachment”—and to the Allies by the code name Tunny (British English for “tuna”). Someone who wished to decode a message by trying every one of Tunny’s possible combinations would have had to look at as many as 4 × 10131 possibilities, more than the estimated number of particles in the universe. By that measure, Tunny’s ciphering system was ten trillion trillion trillion trillion trillion trillion trillion trillion trillion times as complex as Enigma’s.
As a result of their success with Tunny, the men and women of Bletchley Park were able to read the Third Reich’s highest-level military communications system, including messages from Hitler himself. Following a visit to Bletchley Park in 1943, the dean of American cryptologists, William Friedman of the U.S. Army Signal Security Agency, noted in a classified report, “I was astonished to learn that they regard the importance of E [Enigma] traffic to be on the wane and that what they call the ‘Fishes’ traffic is becoming more and more important to them.” The British, Friedman discovered, viewed their Tunny work as “even more secret” than Enigma.
The two world wars, and the years between, were times of tremendous ferment for military technologies. Many of those technologies emerged as a result of more or less impersonal historical forces. Tanks, developed independently in Britain and France during World War I and quickly imitated by the Germans, were probably inevitable in some form during the war as a response to the problems of trench warfare and the machine gun. Heavy bombers, having been enabled by advances in aviation technology, were adopted by many powers either just before or during World War I in response to the perceived needs of total warfare. Radar was invented independently in numerous countries at around the same time in the mid-1930s—including in Britain, Japan, the Soviet Union, and the United States—in response to the problem of bombers, with radar’s foundational technology of radio electronics having been close at hand.
It would be natural to assume Colossus, too, fit such a mold. In truth, however, Britain was not only first, but alone, in using digital electronic computers during the war—for codebreaking or any other purpose. That reflects Colossus having been primarily the result not of impersonal forces but of the joining of extraordinary individuals within an extraordinary institution.
In particular, Colossus owed its existence to the wartime mixing of an improbable trio. The first was Max Newman, a middle-aged mathematician who had joined Bletchley Park several years into the war. He was a mathematical genius from 1940s Central Casting, three-quarters bald, dependent on his round utilitarian glasses; his voice, incongruous with his slight body, was deep and rich in an avuncular way. He had hesitated to apply to work for the war effort, uncertain whether he would be rejected on account of his parentage: his German-born immigrant father had been interned as an enemy alien during World War I and, after the war, left his family behind to return to the old country. Indeed, officials at Bletchley Park were uncertain at first whether Newman’s German origins would disqualify him; he was ultimately told, fortunately for humanity, that they would not be an obstacle in his particular case.
Newman had started at Bletchley Park in a section known as the Testery, so called not because it had anything to do with testing but because its head was a Maj. Ralph Tester. There, Newman wondered whether some sort of machine could somehow help with the Tunny problem. He got the go-ahead and was put in charge of his own section, the Newmanry, to pursue the idea.
The second person who was indispensable to the making of Colossus was Turing, who had been Newman’s protégé at Cambridge. While Turing’s role in breaking Enigma is well known, less remembered are his gifts as a spotter of talent. Newman consulted with his former student on various matters involving Tunny. In the course of these conversations, Turing made his second great contribution to the war effort: he told Newman about Tommy Flowers, a telephone engineer with whom he had dealt on an earlier, Enigma-related project and who had impressed him.
Turing has been mistreated by popular media, which have sometimes presented him as a self-centered, arrogant, condescending, and domineering antihero. In truth, while he was eccentric by any standard, he was a warm and genial colleague, well-liked by his co-workers, drawn to his work by patriotism and the thrill of the intellectual chase. That he was a gay man, which would lead to his prosecution after the war, was known to only a handful of his Bletchley Park co-workers.
Flowers, the third member of the trio, would become Colossus’s designer. The pathbreaking technology of Colossus came not from an advanced alien race but from the son of a bricklayer. As a young man, Flowers had won a competition to become trained in telephone engineering by the Post Office, which ran the British phone system. He had later taught himself digital electronics at a time when it was the province of laboratory physicists. Flowers’s working-class accent invited skepticism from some of the elite minds of Britain’s cryptographic community, and his revolutionary idea of building the machine entirely with electronics was widely considered impossible by the authorities.
Despite his pioneering innovations and his role in the Allies’ war effort, Flowers himself has largely been sidelined by secrecy from the history of computing. His machine, however, would touch many who came into contact with it and saw the marvels of digital electronics for the first time. Not the least of these was Turing himself, whom it would inspire to strike out after the war on a radical new path.
But all of that was in the future. Before any of it could happen, a unique institution would have to be built between the world wars. GC&CS, initially based in London, was for decades a small coterie of intellectual craft workers; their method, to treat decryption problems like brain teasers, to be unraveled with sheer cunning. To meet the dire needs of the war with Hitler, however, the organization would have to transform. While brainpower would always be central to its operation, the scale, methods, and mindset of GC&CS would have to become essentially industrial—and so, painfully, with the aid of a mutiny, they did. Although no one knew it at the time, this transformation would prove essential to Bletchley Park becoming adaptable to Flowers’s machines and exploiting them to the hilt.
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* In classical cryptography parlance, code and cipher refer to two different things. Roughly speaking, codes involve the replacement of a word or phrase with another word or with a number; ciphers involve the substitution of one character for another, character by character, or the rearrangement of characters. In this book, as in most nontechnical usage, the word code is occasionally used to refer to both.
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