This is a story you know, right? It’s early in the war and western Europe has fallen. Only the Channel stands between Britain and the fascist yoke; only Atlantic shipping lanes offer hope of the population continuing to be fed, clothed and armed. But hunting “wolf packs” of Nazi U-boats pick off merchant shipping at will, coordinated by radio instructions the Brits can intercept but can’t read, thanks to the fiendish Enigma encryption machine. Unless something is done – and fast – Hitler’s plan to first bomb, then starve the country will succeed. Enter the genius Alan Turing, working as a codebreaker at the top secret Government Code and Cypher School at Bletchley Park, who, in a generational act of intellectual virtuosity, designs and builds the world’s first computer to crack Enigma, allowing the U-boats to be neutralised and the war ultimately to be won. This is why Turing is known as the father of computing.
It’s a great story. But, like a lot of great stories, it couldn’t be more wrong. The world’s first digital electronic computer, forerunner of the ones reshaping our world today, was built in Britain to revolutionise codebreaking during the second world war – a mind-boggling feat of creative innovation – but Turing wasn’t in the country at the time. Neither was it conceived by the mostly private school and Oxbridge-educated boffins at Bletchley Park. Rather, the machine Park staff called Colossus was the brainchild of a degreeless Post Office engineer named Tommy Flowers, a cockney bricklayer’s son who for decades was prevented by the Official Secrets Act from acknowledging his achievement. Now, with his 120th birthday approaching and a Tommy Flowers Foundation established to right this historical wrong, he is finally getting some of his due, starting with a mural by the artist Jimmy C (best known for the David Bowie mural in Brixton, south London) at the National Museum of Computing.
Here’s the story you didn’t see in the movies.
On a sun-drenched weekday in August, Bletchley Park is the soul of pleasantness: a stately home flanking a lake codebreakers skated on in winter between battling a constantly evolving phalanx of electromechanical encryption machines used to scramble messages between leaders of the Third Reich. On the right as you face the house is a Lego brick complex of concrete huts – grim-looking, as one female codebreaker noted on arrival, but with an aura you fancy you can still feel. I’ve noticed that visitors tend to speak in hushed tones here, as though wary of distracting the brilliant minds still haunting the place. Stephen Fry once declared, “Just saying the name Bletchley Park gives me goosebumps.” Clearly he is not alone.
In the visitors’ centre cafe, one of the Park’s two in-house historians, David Kenyon, explains why the bucolic scene modern visitors encounter needs contextualising. The popular imagining of Bletchley Park (BP) as a determinedly unmilitary scratchpad for eccentric geniuses may have been true in the beginning, he says. But by the end of 1943, when many of the cryptographic breakthroughs had been made, BP was on its way to becoming a codebreaking and intelligence factory underpinning the entire Allied effort. The huts Turing and the cryptographers originally toiled in were now used for minor admin work, while a growing inventory of futuristic codebreaking machines whirred and hummed in a complex of huge lettered blocks built around a communication centre on the far side of the mansion, connected by mechanical conveyors and vacuum tube delivery systems. At peak more than 10,000 people worked here round the clock, in three eight-hour shifts and improbable secrecy. Three-quarters were women, their mean age between 20 and 22.
“Substitution cyphers” such as those the Nazis favoured have existed for at least two millennia. The first known use is recorded by Julius Caesar in his book Gallic Wars, where he describes encrypting a message to his besieged general Cicero by substituting Greek letters for Roman ones. One of the most famous cyphers would subsequently be named for him and involve replacing the original letters of a message (the plaintext) with those a certain number of places along in the alphabet.
Substitution cyphers present obvious points of attack to an enemy. Being able to guess any of the words, for instance “Heil Hitler” at the end of a message, will offer a way in. Letters that appear often, or rarely, or mostly together in the encrypted cyphertext, reflecting patterns in the original message, can offer a toehold. For two millennia cryptography has been a battle of wits between code makers and breakers.
By the time we reached the typewriter-sized Enigma machine, three rotor wheels, like the barrels of a combination lock, were being used to addle plaintext messages. But where the barrels of a combination lock have 10 possible starting positions (0 to 9), these had 26, each corresponding to a letter of the alphabet. And then came the fiendish bit: each letter activated a different substitution alphabet – in one position b might become f, in another q. What’s more, with every plaintext letter typed into the machine, at least one wheel rotates, so changing the substitution alphabet and muddying the patterns on which codebreakers rely.
The British had known about Enigma since 1921, when its manufacturer tried to sell them on it. Dillwyn “Dilly” Knox, a brilliant codebreaker who was said to have been a lover of John Maynard Keynes at Eton and would work closely with Turing at BP, brought one back from Vienna for testing in 1926, when it was found to have small but significant vulnerabilities and rejected. By 1939 and the outbreak of war, a gifted Polish mathematician named Marian Rejewski had broken it “by hand”, with paper and pencil, and with colleagues designed a machine they called Bomba to speed the process. One of Turing’s several acts of genius was to break the more complex naval Enigma machine, before which U-boat wolf packs ran riot in the North Atlantic. Another was designing his own machine, called the Bombe in tribute to his Polish predecessors but vastly more sophisticated than theirs. There’s no way to exaggerate the importance of these contributions. And yet greater challenges lay in wait, leading to a crisis with an outcome no one could have predicted. Enter Tommy Flowers.
By June 1941 most of the work on Enigma was done. That month, however, “Y Service” eavesdroppers at Knockholt in Kent intercepted a Nazi message encrypted in a way they hadn’t seen before. Instead of being transmitted in morse code, like Enigma, this one arrived in teleprinter code, in which each letter was allocated a five-bit binary number. G, for instance, was 01011, equivalent to the decimal number 11. The binary number for each character was then transmitted via rapid pulses and silences – not dissimilar to a 1990s modem.
A teleprinter machine took ordinary typewriter-type keyboard input, converted it to a stream of these five-bit binary numbers and transmitted it. An identical machine at the other end printed the message on tickertape, punching a hole to represent a one and leaving a space to represent zero. Each horizontal line on a teletype tape thus represented a specific character. In the middle of the tape was a smaller sprocket hole used to drive it through the machine.
The mysterious device was active for 16 months of testing, until October 1942, then vanished. British codebreakers dared hope it had been abandoned. Yet almost immediately it reappeared on a line between Berlin and Salonika in occupied Greece – this time to stay. Soon this ghost machine, which the British would never see during wartime, was scrambling traffic on multiple lines, protecting communications between Hitler, his high command and commanders in the field: material of the highest possible order. In keeping with the British characterisation of intercepted messages as fish, the new machine was nicknamed Tunny, for tuna.
Known to German high command as the Lorenz SZ40, Tunny was the size of a laser printer and far more sophisticated than Enigma. It attached directly to a teleprinter and made use of not three or four but 12 wheels, each with a different number of positions, ranging from 23 to 61 (all prime numbers). As per Enigma, the operator of the receiving Tunny machine needed to know the starting positions of each wheel: Bletchley codebreakers called these the wheel settings. But the internal configurations of each wheel could also be changed with the use of small pins, effectively rewiring the machine: BP called these the wheel patterns.
For a year the Research Section at Bletchley strained against Tunny. At first their only hope of a window into the machine rested with enemy carelessness. When, on 30 August 1941, an operator ignored protocol and sent the same message twice without changing the wheel settings, small errors in the second version allowed a veteran cryptanalyst named John Tiltman to deduce 4,000 characters of decrypted text, then infer the wheel patterns (changed monthly at this time). Yet from this high, codebreakers watched in agony as, months later, Nazi high command tightened security, locking them out all over again.
Which is how it stayed for another year, until 25-year-old postgraduate chemist turned mathematician Bill Tutte, in one of the most remarkable intellectual feats of the war, extended an insight of Turing’s that had allowed wheel patterns to be broken and conceived a formula for uncovering the all-important wheel settings. Enough information for any message to be decrypted. But there was a problem. Applying Tutte’s formula to a Tunny cyphertext by hand would take a century or more per message. Still locked out of Tunny traffic except in increasingly rare instances of operator error, the codebreakers’ agony only increased.
The first intake of codebreakers had been light on mathematicians, who were thought too abstracted and weird to trust. Turing’s breakthroughs helped change this, along with a popularity resting on what colleague Peter Hilton called “his original approach to problems of any kind and his quirky and infectious sense of humour”. One beneficiary of the change was a Cambridge don named Max Newman, who found painstaking pencil-and-paper work dull and was on the brink of returning to university when Tunny drew him back.
If you asked Central Casting for a photo of a cerebral academic and they sent you one of Newman, you’d send it back demanding more imagination. There are the round milk bottle glasses; hair battling for headspace with giant brain. In a lecture series in the 1930s, Newman had wondered if intractable maths problems could one day be automated away. He didn’t specify how this would be done, but one of his students – Turing – did, in what is now one of the most famous academic papers ever written, On Computable Numbers. This is the actual reason Turing is “the father of computing”.
The machine Newman now designed to execute Tutte’s formula for attacking Tunny wheel settings was by no stretch a computer in the modern sense, but had the benefit of being relatively quick to build. BP staff named it Heath Robinson for its thrown-together look. And it worked, if with substantial problems, not least being its use of two teleprinter tape loops, one containing the binary cyphertext to be attacked and the other Tunny’s already decrypted wheel patterns, which had to be kept perfectly in sync but tended to stretch, wear and snap. It was also slow and not perfectly reliable. When the team building it ran into difficulties, Turing suggested they consult an engineer he’d worked with and been impressed by. That engineer’s name was Tommy Flowers.
Flowers was born in 1905 in Poplar, east London, the son of a master bricklayer. At 12 he won a scholarship to the local technical college and went from there to an apprenticeship at the Royal Arsenal in Woolwich, then renowned for precision mechanical engineering. Over four years he learned a range of design and manufacturing skills, yet by the end knew mechanical engineering wasn’t for him. What excited Flowers was electricity.
One of the few organisations hiring in the postwar slump of the 20s was the Post Office, then responsible for mail and telecoms and engaged in an ambitious plan to replace their manual phone exchanges with automatic ones. Flowers joined in 1926 and soon built a reputation as an innovative thinker. By the time Turing came calling, he was head of switching research at the Post Office’s Dollis Hill Research Station in north London.
There’s less publicly available information on Flowers than almost anyone else in this tale. But over the line from Washington DC, his niece, Bridget Young, now 82, fills in some of the blanks about his life prior to Bletchley Park. Young went to live with her uncle aged 15, after her father and disabled mother – Flowers’ sister, who he was very close to – died in a car crash. This wasn’t the first familial trauma he’d endured: he was only 25 when his father died suddenly of a stroke, leaving him to assume responsibility for his two sisters and mother, there being no pensions or social safety net in those days. Then one night in October 1940, while he was involved in war work at Dollis Hill, he received news that a bomb had fallen on the family home, killing his mother and youngest sister. He had to go and identify their bodies, as he later would Bridget Young’s parents. For him, the fight against Tunny was personal.
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Nonetheless Young remembers Flowers as warm, playful and curious, a lifetime Labour voter (as were most working people then) who never took for granted the luck he’d had in getting the education he got. She reads me a monograph he wrote in which he laments the inequality of opportunity for working-class children. Going to university never occurred to him. “I had to get a university standard of education by study in my own time without the benefit of actually attending,” he writes.
According to Young, Flowers’ sense of his East End roots never left him. In retirement, when he was stuck on a waiting list for a hip replacement, she offered to pay for it to be done privately – not because he couldn’t afford it but because it might spur him to action – and recalls him telling her, “No, ducks, if my number hasn’t come up, it must be because there are people who need it more than me.” It turned out – in the kind of irony a novelist wouldn’t dare try to fly – the health authority computer had randomly dropped him from the list.
Working in his lab at Dollis Hill, visiting Bletchley as needed, Flowers improved Newman’s design for Heath Robinson and oversaw its manufacture, but still considered it a poor machine. In response, in February 1943, he stunned the boffins with a plan for a fully electronic digital machine that would use thermionic valves as switches to generate and process the zeroes and ones used for binary calculation. Valves – mostly found in guitar amplifiers and high-end hi-fi systems now – look like small, tubular lightbulbs. In the 1940s most people knew them from radio sets, and they had a reputation for constantly failing. Yet, having pioneered their use in automatic telephone exchanges, Flowers knew that if left switched on they were highly reliable.
The idea of using valves as switches in a digital system was so new and radical that Flowers may have been the only person in Britain capable of seeing it – and of knowing they would be millions of times faster than the traditional electromechanical switches Newman used: he had already used them to build a prototype digital memory unit for the Post Office, a truly astonishing first. Nonetheless, Flowers later characterised the response he got at BP as “incredulity”. Nothing like the machine he proposed, using 1,600 valves to perform digital calculations, had ever been contemplated (“What, are you going to throw them at the Germans?” a procurement officer scoffed). Just as mathematicians had been sidelined in favour of genteel denizens of the humanities at first, so building actual things implied “trade”, which tended to be looked down upon. Newman wished him well but pressed on with the utilitarian Heath Robinson.
Turing was different, being someone who loved both making and thinking. He was supportive of Flowers and offered advice on the machine’s logic, but couldn’t be around to provide more than this, because he would be in the US, helping to establish a cluster of US-built Bombes to be run as a BP outpost in Washington DC.
Flowers went away feeling the Bletchley people hadn’t understood him. Luckily his boss at Dollis Hill did and put the Research Station resources at his disposal. Recruitment of able telephone engineers and “wiremen” from around the country yielded a close-knit team of 50 or so, most in their early 20s. Few could be told the purpose of what they were working on, but the intensity of six-to-seven-day work weeks made clear it was important. At one point a resident barber was hired to minimise the need to leave the building.
After 10 months working round the clock, it was done. Colossus weighed a ton and occupied a whole room. Where Heath Robinson used two tapes, Flowers’ machine allowed the Tunny wheel patterns to be programmed into it using plugboards and switches. His original plan was to digitise the Tunny cyphertext being attacked, too, but this was deemed problematic for long messages, so it remained on tape, as rows of holes and spaces representing five-bit binary numbers. The teleprinter tape sprocket holes, conventionally used to drive the tape forward, served to synchronise the whole machine, functioning like the “clock” in a modern computer. Which is what Flowers and his team of young Post Office engineers had built: the world’s first special purpose electronic digital computer.
Delivered in a Post Office truck to BP on 18 January, the prototype was assembled by Flowers’ people and worked almost immediately. Its first job, for a cyphertext whose decrypt was known, took 10 minutes. Flowers later marvelled that “when the first machine was constructed and running, they couldn’t believe it”. More were ordered, to be produced in a commandeered Birmingham Post Office factory at a rate of one a month, with the enhanced Colossus II involved in a race to be ready for D-day in June 1944 (though whether it had a specific role in D-day is unclear). Subsequent models included many new features and innovations, with a later example including what one of the Colossus team proudly describes as “a relatively large semi-permanent memory”, equivalent to Ram. By VE Day 10 machines were working round the clock in two giant steel-framed buildings: a codebreaking factory.
After the war, Churchill ordered most of the Colossi to be destroyed, with all information about them classified. Two went to GCHQ, where they remained in use until the 1960s. One, or possibly two, were disassembled and, with parts scrubbed of clues to their previous use, went with Newman to Manchester University, to help build the world’s first general purpose computer, soon taken to market as the Ferranti Mark I. Turing went to the National Physical Laboratory in London, where he built the most sophisticated computer of the immediate postwar years, the ACE.
Both Newman and Turing have long (and rightly) been considered seminal figures in the annals of computing. No one seems to have guessed they were shown the way by a working-class Post Office engineer. Meanwhile, two years after Flowers delivered Colossus, he was forced to watch the Americans John Mauchly and J Presper Eckert being feted as visionary builders of the first computer, the ENIAC, and enriched accordingly; to see their claim repeated in history books for the next 50 years, unable to say anything in reply. Worse, when he tried to persuade the Post Office to modernise with the technology he pioneered, managers didn’t believe he could make it work and thought him pretentious for suggesting he could.
Full details would take another five decades to be declassified. By then, a computer scientist named Tony Sale, fresh from campaigning to save BP from property developers, had begun a rebuild of a Colossus, which now lives at the Bletchley-based National Museum of Computing. After speaking with the historian David Kenyon, I amble round the corner for a treat: not just to see Colossus, but to see it running. In operation it’s majestic, all crisply spooling tape and flashing lights, and surprisingly smooth-running; the kind of conceptual leap the world doesn’t see often. I’ve been lucky to meet a lot of charismatic machines, but few have the kind of presence this one does.
Jack Copeland is professor of philosophy at the University of Canterbury, Christchurch, and director of the Turing Archive for the History of Computing. Any article or discussion of Turing or Colossus owes a huge debt to his work and this one is no exception. If anyone is well placed to provide perspective on Flowers’ life and achievements, he is.
“Of course, Tommy couldn’t have patented anything he’d done,” he tells me over Zoom. “He should be up there with Bill Gates and Steve Jobs and all the rest of them, one of the great figures of the history of computing. He should have made as much money as they did, certainly as much as Eckert and Mauchly did.”
Copeland met and interviewed Flowers before he died in 1998, just as a new tranche of material relating to Tunny and Colossus was being released. How was the engineer feeling about his deferred recognition?
“You know, I think he was over it by then. I remember one day bouncing in, full of the joys of spring, saying, ‘Hey, there’s going to be a book’” – the monumental Colossus: The Secrets of Bletchley Park’s Codebreaking Computers, which Copeland edited – “‘and it’s going to tell the whole story.’ He just sort of … looked interested, but he said, ‘It’s too late. It’s much too late.’”
Bridget Young is pleased her beloved uncle got to see his achievements acknowledged finally, even if most people still think Turing built Colossus. But she recalls someone who was mostly happy; who in retirement was still acquiring ambitions and enthusiasms, from painting to playing bassoon in an orchestra.
“You know, I have three kids and my older son was always fascinated by Uncle. He used to get a magazine called Cricket and somebody wrote an article about the first computer, the ENIAC computer. So Daniel, who must have been about seven, wrote them a letter saying, ‘No, they weren’t the first, my uncle was!’ And Cricket printed the letter, so I sent a copy to Uncle, saying, ‘Look, you’ve got somebody standing up for you.’ And Uncle wrote Daniel this wonderful letter, in which he thanked him for defending him, then said, ‘You know, when a new discovery is about to be made, it’s usually happening in several places at the same time, because different developments, in different disciplines, are all making different moves forward, until enough is known that a new step is needed. It’s never just one person in one place.’ I think for him the reward was what he and the others all did together.”
