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VDOI:10.1145/3018994 Thomas Haigh Historical Reflections Colossal Genius: Tutte, Flowers, and a Bad Imitation of Turing Reflections on pioneering -breaking efforts.

AY 14, 2017, will be the 100th anniversary of the birth of someone you might not have heard of: William Thomas (“Bill”) Tutte. MDuring the Second World War he made several crucial contributions to decrypt- ing the Lorenz used to protect the Nazi high command’s most cru- cial radio communications. This work provided the statistical method imple- mented electronically by Tommy Flow- ers, a telecommunications engineer, in the Colossus machines, which pio- neered many of the electronic engineer- ing techniques later used to build digi- tal computers and network equipment.a

Myths of The British code-breaking effort of the Second World War, formerly secret, is now one of the most celebrated aspects of modern British history, an inspiring story in which a free society mobilized its intellectual resources against a ter- rible enemy. That’s a powerful source of nostalgic pride for a country whose national identity and relationship with A scene from the 2014 film with actor its neighbors are increasingly uncertain. portraying . Tutte’s centennial gives a chance to con- sider the broader history of Bletchley and the way in which it has been remem- ably comes from the Oscar-winning Park, where the codebreakers worked, bered. Some kinds of people, and work, film The Imitation Game. This gives us have become famous and others have a starting point: the film is a bad guide not. to reality but a useful summary of every- a This column draws on a research project in progress I am conducting with Mark Priest- Films reach more people than books. thing that the popular imagination gets ley, supported by L.D. Rope’s Second Chari- So statistically speaking, most of what wrong about Bletchley Park.

PHOTO BY SNAP STILLS/REX/SHUTTERSTOCK BY PHOTO table Settlement. you know about Bletchley Park prob- One myth is that Alan Turing won

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Figure 1. Logical representation of the action of the Lorenz machine, dubbed “Tunny” by the when the correct settings have been British. The gap of four characters shown between the chi and psi wheels is to symbolize found. Enigma is broken! In reality this the idea of two logically independent transformations applied to a five channel bitstream, was not something that occurred to rather than a representation of the actual inner working of the machine. Turing only after he had finished build- ing a completely pointless machine, Source Lorenz Encoding Attachment but basic cryptanalytic practice already used to break Enigma manually. (paper 1 0 0 1 1 XOR χ1 1 0 1 1 XOR ψ1 0 0 0 radio tape or 0 1 0 1 0 XOR χ2 0 0 1 0 XOR ψ2 1 0 1 Even with the , breaking Enig- transmitter real time 0 1 0 0 0 XOR χ3 1 1 0 1 XOR ψ3 0 1 0 ma continued to rely on a mix of human keyboard 1 0 1 1 0 XOR χ4 1 0 1 0 XOR ψ4 0 0 0 skill, manual methods, and machine entry) 1 0 0 1 0 XOR χ5 1 0 0 0 XOR ψ5 1 0 1 power. Each Bombe was tended by a cipher text plain text µ1 µ2 (5 bit channels) (5 bit channels) team of female operators, and in recent 5 chi wheels 2 motor 5 psi wheels years a lot of attention has been paid to always wheels drive sometimes rotate psi wheels rotate the experiences of these women. The serialized Bombe operators and Enigma decryp- ciper text ters worked in factory-like conditions, Same wheel start positions and bit patterns used on encoding and decoding machines in a massive operation pioneered by for the group at- 01101 11101 01011 00101 tacking Air Force Enigma. Welchman Printer Lorenz Decoding Attachment had made his own vital contribution (Types out 1 1 0 0 1 XOR χ1 1 0 1 1 XOR ψ1 0 1 1 to the Bombe’s design, a “diagonal radio message 0 1 0 1 0 XOR χ2 1 0 0 0 XOR ψ2 1 0 1 receiver board,” but after the machines arrived as received) 0 0 0 1 0 XOR χ3 1 1 0 1 XOR ψ3 1 1 1 0 1 1 0 1 XOR χ4 1 0 1 0 XOR ψ4 0 0 0 shifted to overseeing their use. In con- 0 1 0 0 1 XOR χ5 1 0 0 1 XOR ψ5 0 0 1 trast, once logistical challenges began cipher text plain text µ1 µ2 to outweigh conceptual ones Turing drifted away from leadership of the corresponding group tackling Naval Enigma. There are many kinds of ge- the war pretty much by himself. Bene- and eventually triumphing. In reality, nius, and Turing’s was not of the mana- dict Cumberbatch played Turing as Turing was far from a marginal and de- gerial variety. television’s Sherlock: a humorless, asex- spised figure at Bletchley Park, moving By early 1945 more than 10,000 peo- ual loner whose superhuman mental quickly to a leadership role. The ob- ple worked directly on the British code- powers are compromised only by an stacles Cumberbatch faces are mostly breaking effort. Most of them were almost autistic indifference to social fictional and often absurd. His boss (in women. The film directs some heavy- norms. This combines the traditional reality Turing’s subordinate) Hugh Alex- handed sexism at , a rare focus of popular science writing on ander tries to smash Christopher. Like female cryptanalyst, to give viewers a the lone genius who changes the world all military men , the chance to feel superior to their grand- with the modern movie superhero nar- head of Bletchley Park, is a belligerent parents. Word at Bletchley Park was rative of a freak who must overcome idiot. He smashes down the door, hop- indeed deeply stratified by class and his own flaws before he can save the ing to have Christopher destroyed. A gender, and cryptanalytic work of the world. (This is, I understand, exactly the little later Cumberbatch is blackmailed kind done primarily by upper middle same arc Cumberbatch follows in Doc- into passing secrets to a Soviet spy. class men like Turing has traditionally tor Strange, a literal superhero movie). Cumberbatch’s growth is symbolized been the most celebrated. Yet its own A team of six bright young men arrive by his making friends with the other erasure of the work routinely done by at Bletchley Park and are given the job brilliant codebreakers, but they seem women reflects a more modern sexism. of breaking the German Enigma code. just as arrogant as he was. Fearful that A single giant machine, given by a su- After introducing himself as “the best Bletchley Park managers will get in the perman, clunks without human inter- mathematician in the world,” Cumber- way, they pretend that Enigma is unbro- vention until the answer emerges. batch dismisses his fellow codebreak- ken and instead run the Battle of the At- That’s silly. So is the myth that bril- ers, saying “I don’t have time to explain lantic from their machine room, decid- liant scientists need no help from engi- myself as I go along, and I’m afraid ing which convoys to save and which the neers. Cumberbatch drew up the engi- these men would only slow me down.” U-boats should be allowed to sink. neering blueprints for the one and only Over their objections, and the opposi- Another myth is that code-breaking Bombe during a montage, then built it tion of almost everyone else at Bletch- machines eliminated human labor at Bletchley Park aided by a handful of ley Park, he designs a machine called and code-breaking skill. At first Chris- briefly glimpsed assistants. In fact, ap- Christopher to beat Enigma. topher spins uselessly, producing proximately 200 were manufac- The film struggles to shoehorn a dramatic tension but no Enigma set- tured, none of them at Bletchley Park, complicated, nuanced, and tragic sto- tings. At the last minute, Cumberbatch with design and production work done ry into the generic template of a hero thinks of looking for the common primarily by the British Tabulating Ma- overcoming obstacles, facing disaster, phrases, such as “Heil Hitler,” to detect chine Company, under the direction of

30 COMMUNICATIONS OF THE ACM | JANUARY 2017 | VOL. 60 | NO. 1 viewpoints its chief engineer . BTM had Tunny before Tunny, with the result that early licensed IBM punched card technology There’s another popular myth en- histories assumed that all intelligence for sale throughout the British Empire, dorsed by the The Imitation Game: that delivered by Bletchley Park had come giving it command of the necessary the Enigma was the only significant from Enigma. technologies and engineering methods. German cipher broken at Bletchley The British knew nothing about the In this way, and countless others, Park. In reality another cipher, code- machine producing Tunny, working technology transcended, rather than named Tunny, was just as important. entirely on clues from the intercepted supplemented, human labor and bu- Enigma was used by the German mili- messages. In contrast, the team break- reaucracy. Perhaps nobody would pay tary to communicate with forces in ing Enigma had a number of resources to see a movie centered on heroic pro- the field. Compact code boxes flashed to draw on. Enigma technology had duction engineers, brilliant Bombe op- up the appropriate letter of cipher- been sold commercially since the erators, and inspirational government text each time a was pushed. The 1920s, so its architecture was pub- procurement specialists, but would encrypted version of the message was lic. The German government speci- it be so difficult to give walk-on parts transmitted by a human using Morse fied modifications but Polish teams to the people who actually designed, code. Tunny was used by the German had broken earlier military versions. built, and operated the Bombes? It’s High Command to communicate with They passed their secrets, and the ini- not like leaving them out makes the generals outside the reach of wired tial Bombe design, on to the British firm particularly entertaining: political communication links, such as the divi- at the start of the war. Even the name comedian John Oliver recently likened sions deep inside the USSR. Messages “Bombe” came from the Polish “bom- a hellish commute requiring three bus- typed on a keyboard were encrypted, ba kryptologiczna.” Captured German es and two trains to “the length of the transmitted by radio, and automati- personnel, code books, keys, and man- movie The Imitation Game—two wasted cally decrypted and printed at the oth- uals provided more clues to changes in hours that feel like forever.” er end. Enigma was declassified long Enigma technology and practice.

Figure 2. The overall Tunny interception and decryption workflow process as of late 1944. While Colossus machines could also be used to tackle the Psi wheels, the increased pressure of work after the Germans began daily changes to wheel patterns meant that this part of the job was usually done in the without Colossus assistance.

serialized ciper text English Cipher text of one message plain text (5 channel tape) 1 0 0 1 1 0 1 0 1 0 0 1 0 0 0 They were already 1 0 1 1 0 looking at him as 1 0 0 1 0 approached in the distance, because he just stood out. He had quite an old face, but from the way he walked, 01101 11101 01011 00101

Knockolt Newmanry Newmanry Testery Testery Outstation Set Chi Wheels Generate Set Psi & Decrypt Translate Intercept, & Verify Counts “dechi” Motor Wheels Message Message Record & (Reverse- (Reverse- Verify (Colossus) engineered (Hand methods) engineered (Bilingual Message Tunny machine) Tunny machine) humans)

dechi

1 0 0 1 1 0 27, 12, 30, 43, 8 Sie sahen ihn schon Chi wheel 0 1 0 1 0 1 Psi & 55, 22 von weitem auf sich 0 1 0 0 0 zukommen, denn er start posns. 1 0 1 1 0 1 0 0 1 0 motor start posns. fiel auf. Er hatte ein for msg ganz altes Gesicht, aber wie er ging, daran 31, 3, 25, 18, 5 sah man, dass er erst zwanzig war. German 1 0 0 1 1 0 0 1 0 1 0 1 0110001010... plain text 0 1 0 0 0 Newmanry 1 0 1 1 0 0011010100... 1 0 0 1 0 10011001001... 01100010110... 1 0 0 1 1 0 Break Chi 0 1 0 1 0 1 01011001101... 0 1 0 0 0 Wheels 0110001010... 1 0 1 1 0 Chi wheel 0011010100... 1 0 0 1 0 Testery patterns 10011001001... 1 0 0 1 1 0 (Colossus & 01100010110... 0 1 0 1 0 1 “rectangling” (apply to 01011001101... 0 1 0 0 0 Break Psi 10110010111... 1 0 1 1 0 all messages 1 0 0 1 0 method) & Motor Wheels 01101101001... on that link) 1 0 0 1 1 0 Psi & motor 0 1 0 1 0 1 (manual 0 1 0 0 0 wheel patterns 1 0 1 1 0 methods 1 0 0 1 0 (apply to incl. “Turingery”) all messages Cipher text of multiple messages on that link) from the same radio link

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The first challenge was to figure out the Tunny machine a new group, named first set, known at Bletchley Park as the structure of the machine that had the Testery after its head, Major Ralph the chi wheels, rotated to the next po- produced the Tunny messages. This Tester, went to work breaking its mes- sition each time a character was read, relied on operator error. In August sages. While seconded to the research whereas the second set, the psi wheels, 1941 a long message was sent twice, section, Turing came up with a method turned only when directed to do so by with minor alterations, using the same for figuring out the bit patterns on the two “motor wheels.” Decrypting a Tun- machine settings. Comparing the two coding wheels once the keystream had ny message posed two main challeng- messages let Brigadier John Tiltman been successfully isolated. The crypt- es. First to set the chi wheels, using this piece together the original (“plain”) analyst formed and tested hypotheses information to generate “dechi,” text text of each message and the encoding to gradually extend the known portion encrypted only by the psi wheels. Then sequence (“key stream”) with which of the wheel pattern. “Turingery,” de- to set the psi and motor wheels, using each had been combined to yield its scribed by Tutte as “more artistic than this information to generate plain text. cipher text (see Figure 2). This nicely mathematical” made wheel breaking Because the psi wheels did not al- disproves the idea that Bletchley Park’s feasible, if arduous. ways rotate, their contribution to the ci- experienced military men were there Both wheel setting and wheel break- pher text often repeated from one char- primarily to frustrate Turing. ing depended on luck, ingenuity, and acter to the next. This, Tutte realized, German errors, but because wheel set- gave a statistical method to set the chi Tutte’s Breakthroughs ting had to be done for each message it wheels without making any assump- Tutte used these sequences to make proved the biggest constraint. Until Oc- tions about the psi wheels. Whether the breakthrough. Shortly after the tober 1942 the German operators were the wheels moved or not they still outbreak of war he had joined Bletch- kind enough to precede each message masked the distinctive character distri- ley Park’s “Research Section,” which with a series of 12 unencrypted letters, butions of German text. But whenever had responsibility for investigating each coding the position for one of the the psi wheels did not rotate, the deltas unfamiliar codes and devising meth- wheels. Clues of this kind made the between successive characters would ods that could be used to break them work of the codebreakers much easi- pass through them unchanged. on a production basis. Like many of er, as hints obtained from decrypted Analyzing a sample of decrypted his colleagues he had a Cambridge de- messages were applied to others sent messages showed him that the distri- gree, though as the son of a gardener on the same link. Their results were bution of deltas was far from random. his social background was unusually sporadically impressive, but improve- For example, in German “ei” is a very humble. His first degrees were in phys- ments in German practice threatened common string. E is (1,0,0,0,0) and I is ical chemistry, but his interests were to close the door entirely. (0,1,1,0,0). Their delta, (1,1,1,0,0) had already shifting to mathematics. At this point Tutte made his sec- a frequency of 5.9%—almost twice as Looking at the teleprinter tape five ond huge contribution. When setting common as in a random distribution. channels separately Tutte noticed a wheels it was easy to determine statisti- The delta between two repeated char- regularity every 41 characters in the cally whether a particular combination acters, (0,0,0,0,0), occurred 4.6% of the key sequence. This gave the clue that a yielded natural language or random time. German has many double “s” 41-character code wheel was involved. noise. Trying every possible combina- characters, and teleprinter operators Step by step, Tutte’s team worked out tion of positions across the 12 wheels often pushed the shift and unshift keys, the full, complex structure of the Lo- was clearly impossible: the war would encoded as their own characters, twice renz machine and its 12 code wheels be over, and the Earth swallowed up to make sure that they were received. (see Figure 1). Three kinds of informa- by the sun, long before the job was fin- When the distribution of deltas in tion were needed to decrypt a Tunny ished. But flaws in the design of the successfully dechied text was plotted the message. Tutte had provided the first, Lorenz machine made it possible to same tell-tale “bulges” in the distribu- by reverse engineering the Tunny ma- break the job into tractable steps. Each tions of deltas appeared. If the psi wheels chine’s internal structure. From this channel was encrypted by the succes- moved about half the time the peaks and the British built their own Tunny de- sive action of two code wheels. The valleys would be half as tall but follow crypting machines. the same pattern. However, if dechi was Two challenges remained. The sec- produced with the wrong wheel settings ond piece of information was the posi- Another myth is the distribution of deltas should be close tion of each of the wheels at the start to random, with all combinations occur- of a message. Finding this was called that code-breaking ring about 3.1% of the time. “wheel setting,” and had to be done machines eliminated Setting chi wheels meant generat- for each message. The third was the bit ing dechi with different wheel com- pattern set up on each of the wheels. human labor and binations and looking for a non-ran- These were regularly changed by flip- code-breaking skill. dom distribution of deltas. The five ping tiny pins. Finding these sequenc- chi wheels could take 22 million com- es was called “wheel breaking,” and binations, but because each acted on was performed less frequently as most only one of the five bit channels that changed only monthly or quarterly. encoded each character there was no After Tutte cracked the structure of need to consider all wheels simulta-

32 COMMUNICATIONS OF THE ACM | JANUARY 2017 | VOL. 60 | NO. 1 viewpoints neously. The five most common deltas sages a day, but by March, with the first were (1,1,0,1,1), (1,1,1,0,0), (0,0,0,1,0), Colossus still not fully operational, this (1,1,1,1,1), and (0,0,0,0,0). In each Technology had already risen to 20. More machines case first two channels were either transcended, rather were ordered. Here too work was seg- (1,1) or (0,0) and so added to 0. May- regated: cryptographers (overwhelm- be your school didn’t teach you that than supplemented, ingly male and upper middle class) 1+1=0, but in this context “addition” human labor directed female Colossus operators. meant the logical operator XOR. Tutte Once chi wheel settings were known devised a very simple method: (a) use and bureaucracy. then psi and motor wheel settings were all 1,271 possible wheel start posi- usually performed in the Testery. Using tions to generate dechi for channels 1 linguistic knowledge and craft skills, and 2, (b) for each dechi stream count rather than mechanical aids, it took the number of positions where deltas about an hour to identify the correct for channels 1 and 2 add to 0, (c) take settings for a message if things went the wheel settings with the highest chines, the prototype read two looped well. Bletchley Park had, after all, delib- count. Once settings for the first two paper tapes. When implementing erately recruited champion crossword wheels were found the process was re- Tutte’s method one would hold the solvers. Colossus could handle this job, peated to identify the others. If every- message text and one the coding key but usually helped out only when spare thing went well, this would set all five series produced by a particular pair machine time was available. Once all wheels by processing the encrypted of chi wheels. Dollis Hill’s experi- settings were known women, mostly message about 2,400 times. ence with telegraphic equipment, from working class backgrounds, oper- Here, at last, was a way of breaking and Flowers’ personal enthusiasm ated machines to decrypt the messag- Tunny messages that did not depend on for electronic signal processing, came es. The Tunny messages were translat- German laxity. It was possible to verify together in an optical sensing sys- ed by a mixed-gender group of middle Tutte’s method with hand calculation, tem, able to coordinate the two tapes class university graduates, analyzed by but no manual method that involved at up to 2,000 characters per second. male intelligence specialists, and filed comparing lengthy sequences so many This allowed it to evaluate all possi- by women in a massive repository in- times would ever be practical for pro- ble combinations for the first two chi dexed with punched cards.b duction use. The success of the Bombes wheels in about half an hour. After the Tutte realized that his statistical against Enigma made mechanization prototype proved itself, during testing method could also, given a sufficiently the obvious solution. , a in mid-1943, Dollis Hill built several long message, be used to break wheels. Cambridge mathematics lecturer, was more Robinsons. The technique was called “rectangling” put in charge of a small group exploring Back in March 1943, Flowers had because it involved making a large ta- machine methods for Tunny. also persuaded Newman to endorse ex- ble tabulating every possible position perimental work on a machine able to of two wheels. The first two chi wheels Flowers and Colossus simulate Tunny code wheels electroni- repeated themselves every 1,271 char- Enter our third major protagonist, Tom- cally rather than read them from tape. acters, meaning a very long message my Flowers. Flowers came from a work- With no need to synchronize two tapes might contain a dozen or more charac- ing class background, earning a degree the message could be run at 5,000 char- ters encoded with each possible wheel in night school while working as an ap- acters per second. More importantly, combination. Whenever the psi wheels prentice. He rose through the engineer- it became much easier to change bit did not rotate, the sum of the deltas ing ranks of the General Post Office, patterns or set new combinations of from the encrypted message would be the government monopoly responsible wheels. This reduced set up time be- the same as the sum of the deltas on for telephone and telegraph service as tween runs, and opened the door to the corresponding channel of the chi well as mail delivery. By the time the war new analytical tactics. As well as cram- wheel sequence and the plain text. Be- began he was the leading electronics ming electronic vacuum tubes into the cause the deltas of the first two chan- specialist at the Post Office’s Dollis Hill simulated code wheels, Flowers used nels of plain text were disproportion- research station. In January or February them liberally in its counters and in the ately likely to sum to zero, this exposed 1943, Newman arranged for a contract logic circuits used to combine inputs information about the wheel patterns. with Dollis Hill to build parts of a pro- in different ways. The first Colossus, The encrypted message deltas tallied in totype machine able to apply Tutte’s delivered to Bletchley Park in January each cell of the table gave clues about statistical method. Flowers, and others 1944, had approximately 1,500 tubes, the sum of the deltas of the two cor- at Dollis Hill, had already been work- a huge number by the standards of the responding code wheels. A high score ing with Bletchley Park to explore the day, but Flowers later said he knew it application of electronic, rather than could run reliably because of his pre- b The gender and class background of the dif- mechanical, sensing units to the next war experiments with a prototype elec- ferent jobs is taken from Christopher Smith, generation of Bombes. tronic telephone exchange. The Hidden History of Bletchley Park, Palgrave, 2015. The work of Colossus operators is dis- Nicknamed “Heath Robinson,” Colossus delivered a huge produc- cussed in Abbate, J. Recoding Gender: Women’s after a British cartoonist known for tivity boost. In February Newman’s sec- Changing Participation in Computing. MIT drawing improbably complex ma- tion was setting only four or five mes- Press, Cambridge, MA, 2012.

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pointed to a delta total of one, a low than expected. The more I look at those score to a total of zero. Codebreakers other projects of the 1940s the more worked from estimates of the delta to- Newly declassified amazed I am that the Dollis Hill team tals back to the separate deltas on each information gives had the first Colossus installed and wheel, using a technique similar to the working at Bletchely Park less than a solving of a “magic rectangle.” These us a better sense of year after pitching it to Newman. candidate wheel deltas were then set just how impressive up on Colossus, and varied over many Remembering and Forgetting runs to maximize fit with other mes- Colossus was. Back to The Imitation Game, which never sages using the same wheel patterns. mentions Tunny, Flowers, Colossus, or Later versions of Colossus included Tutte. The end of the movie takes place an extra control panel, making it eas- several years after the war. Cumber- ier to set up and test candidate wheel batch’s Turing is coming apart mentally patterns without going around to the after being sentenced to compulsory back of the machine. Once the deltas figurable logic was stateless, used only hormone treatments intended to con- for each wheel were established deriv- to combine the current set of inputs to tain his homosexual urges. He bumbles ing the raw wheel patterns was trivial increment, or not increment, each of around his house in a bathrobe, drifting in comparison. Wheel breaking, like its five counters. The counters retained toward suicide, distracting himself only wheel setting, no longer relied on slips state from one tape character to the by building another Christopher. To by the German operators. This was just next, but the logic networks could not send the audience out on a more cheer- as well, because in July 1944 they start- access this information. Neither was it ful note, Joan Clarke, his friend and for- ed changing all wheel patterns daily. programmable, as its basic sequence mer fiancée, visits to point out that she of operations was fixed (though many had “just taken a train through a city Colossus in Context parameters could be set with switch- that would not exist if it wasn’t for you. Turing is often misidentified by es). Colossus was a milestone in the I bought a ticket from a man who would journalists as the creator of Colos- development of digital electronics, in- likely be dead if it wasn’t for you.” sus. As I discussed in a previous col- corporating many of the circuits and When victory was declared, Cum- umn, the “Matthew Effect” means hardware features later used to build berbatch boasted that “the war was that all the credit for any technical computers. But it had a quite different really just a half-dozen crossword en- achievement tends to go to the most purpose, and different architecture, thusiasts in a tiny village in the south famous person tangentially asso- from an electronic computer. of . Was I God? No. Because ciated with it. The Imitation Game Newly declassified information God didn’t win the war.” I’m sure that further confuses this: “I want Chris- gives us a better sense of just how im- the real Turing never dismissed the topher to be … a digital computer” pressive Colossus was. During the war millions who fought and died in this Cumberbatch says of his Bombe, af- the U.S. commissioned dozens of dif- way. He wasn’t an idiot. But beneath ter being asked whether he is trying ferent specialized code-breaking ma- the film’s sepia nostalgia lies a very to build a Turing machine. chines from prominent companies and modern delusion: established insti- This seems to deliberately blur the research centers such as IBM, NCR, tutions (such as government and the Bombe with Colossus, which has often Bell Labs, and MIT. Almost without ex- military) are so dysfunctional, and or- been called “the first programmable ception the most technologically am- dinary people so irrelevant, that tech electronic computer,” though Flowers bitious projects, such as microfilm and geniuses must secretly seize power. himself was ambivalent about calling it electronic memories, were late, aban- To put that another way, Turing a computer in his talks and articles. He doned before completion, or proved so wasn’t Peter Thiel. saw it as a “processor,” part of the evolu- unreliable as to be useless. Even some Tutte made the same kind of daz- tion of digital bit stream manipulation of the more technologically conserva- zling intellectual contributions as Tur- toward his dream of a fully electronic tive projects, such as a million-dollar ing to the success of Bletchley Park. telephone exchange. After working with giant Bombe built by Bell Labs, fizzled But brilliance alone does not win one Mark Priestley on a detailed analysis of in use because they were constructed the kind of fame that culminates in a Colossus I agree with Flowers. Colos- without a good grasp of code-breaking glossy scientific biopic—an extremely sus could be set up to combine input practice.c Likewise, pretty much all rare honor. After earning his Ph.D. in bitsteams from tape and the simulated post-war electronic computers, which 1948 Tutte followed the trajectory of code wheels in many different ways, like Colossus depended on making his wartime work into a distinguished running the selected inputs through a thousands of vacuum tubes work mathematical career focused on network of logic gates. This gave it the together, were plagued by reliability graphs and matroids. He is well re- flexibility to carry out many different problems and took far longer to finish membered in those fields, and his war- Tunny-related attacks. Because it did time contribution is documented, for not include any hardware for arithmetic those who care, in several histories of c These projects are described in Burke, C.B. It calling it a computer confuses things, Wasn’t All Magic: The Early Struggle to Automate Bletchley Park. Tragedy and drama at- whether we go by today’s meaning of , 1930s–1960s. National Security tracted Hollywood to the lives of Alan the word or 1940s definitions. Its con- Agency, 2002. Turing, Stephen Hawking (The Theory

34 COMMUNICATIONS OF THE ACM | JANUARY 2017 | VOL. 60 | NO. 1 viewpoints of Everything), and John Nash (A Beau- have celebrated Colossus as a founding University Press, Princeton, NJ, 2014. The tiful Mind). Contentment is not as ex- contribution to digital technology. Imitation Game was nominally based on citing to watch as tragedy, but most of The real story of Bletchley Park is Hodges’ landmark biography of Turing, but don’t let that put you off. He’s maintained a us would prefer it for ourselves. I don’t one of teamwork on a massive scale, tactful silence about the movie. think Tutte minded this relative ne- in which good management and ef- McKay, Sinclair. glect—he appears to have lived a long, fective procurement were just as im- The Secret Lives of Codebreakers: The happy, and active life full of scholarly portant as individual scientific ge- Men and Women Who Cracked the Enigma accomplishments and recognition, nius. Tutte and Flowers did not win Code at Bletchley Park. Gives a fascinating including appointment as a Fellow of the war by themselves, any more than window onto the social history of Bletchley the Royal Society and even the posthu- Turing did. But, whether or not the Park and the experiences of the people who worked there. mous naming of an asteroid. Colossus story ever makes it to the Flowers was less satisfied than Tutte big screen, each played an outsize Randell, Brian. “The Colossus.” In Metropolis, N., Howlett, with his career, never entirely realizing role in the defeat of fascism. J. and Rota, G.-C. eds., Academic Press, New his vision for a fully electronic telephone York, 1980, 47-92. This paper broke the public exchange. His relative obscurity reflects silence surrounding Colossus, at a time when a larger tendency to remember concep- Further reading the British government was still actively suppressing the release of information. tual breakthroughs and ideas, which Copeland, Jack. fit the stereotype of individual genius, Colossus: The First Electronic Computer. Welchman, Gordon. rather than system building accomplish- , New York, 2006. The Hut Six Story: Breaking the Enigma ments, which are inherently team based. A compendium of analysis, reprinted Codes (McGraw Hill, 1982). The most historical documents and memoir. substantial first person account of He lived to experience a small measure Contains Tutte’s own description of his Bletchley Park, focused on Enigma of fame for his work on Colossus, but breakthroughs against Tunny. rather than Colossus. seemed bitter, complaining that his ca- Gannon, Paul. Thomas Haigh ([email protected]) is a Visiting reer was over before he could benefit Colossus: Bletchley Park’s Greatest Secret Professor at Siegen University and an Associate Professor from this newfound respect. His reputa- (Atlantic Books, 2006). The clearest overall at the University of Wisconsin—Milwaukee. He is the history of Colossus. primary author of ENIAC In Action (MIT Press, 2016). tion has continued to grow, and in the Read more at http://www.tomandmaria.com/tom past few years a postage stamp and a dis- Hodges, Andrew. play in the Science Museum in Alan Turing: The Enigma. Princeton Copyright held by author.

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