Case S01E15 – Enigma, part 3 of 3

CONTENT RATING: PG-13 (themes: war, death)

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Enigma was one of the most advanced mechanical ciphers of its time. In this final episode, as war consumes Europe, Alan Turing and Bletchley Park take on the ultimate version of the Enigma mechanical cipher – the naval Triton M4. Below you will find data, audio credits, further reading, and a transcript of the podcast.

Did you like this podcast miniseries? Would you have changed anything? Want something different? More of the same? This Festival of Social Science event was supported by the ESRC and they’d love to know your views on it, so if you have a moment, please fill in this quick survey to let them know your thoughts.

Audio credits

Scott Holmes – Business Gateway
Kai Engel – January [Cold]
Kai Engel – December [Cold]
Kai Engel – Blizzard PON I [Cold]
Kai Engel – Brooks [Mild]
Kai Engel – Sentinel [Satin]
Kai Engel – Homeroad [Satin]
Lee Rosevere – Healing

Credits, sources, and more

Bletchley Park (2019). Podcast. Available at <>

Corera, G. (2014). “Poland’s overlooked Engima codebreakers”, BBC News (Warsaw), 5th July 2014. Last accessed 10th July 2019. Available at: <>

Dziewanowski, M.K. (1994). “Polish Intelligence During World War II: The Case of Barbarossa”, East European Quarterly, 28(3), 381-391.

Helm, S. (2015). If This Is A Woman. Inside Ravensbrück: Hitler’s Concentration Camp for Women. London: Little, Brown Book Group.

Kozaczuk, W. (1984). ENIGMA: How the German Machine Cipher Was Broken, and How It Was Read by the Allies in World War Two. London: Arms and Armour Press.

Kuhl, A. (2007). “Rejewski’s Catalog”, Cryptologia, 31(4), 326-331.

Lelwic, J. (2005). “Marian Rejewski – the man from Bydgoszcz who helped the allies win the war”. In: J.S. Ciechanowski, J. Garbowski, E. Maresch, H. Piechocka-Lipka, H. Sowińska, and J. Sylwestrzak (Eds.), Rejewski: Living with the Enigma Secret (pp. 45-66). Bydgoszcz: Bydgoszcz City Council.

Milner-Barry, S. (1993). “Hut 6: Early days”. In: F. H. Hinsley and A. Stripp (Eds.), Codebreakers: The Inside Story of Bletchley Park (pp. 89-99). Oxford: Oxford University Press.

Mollin, R.A. (2005). Codes: The Guide to Secrecy from Ancient to Modern Times. Boca Raton: Taylor & Francis Group.

Oleksiak, W. (2014). “The Hacker Who Saved Thirty Million Lives”, Last accessed 10th July 2019. Available at: <>

Rejewski, M.  (1981). “How Polish Mathematicians Deciphered the Enigma”, Annals of the History of Computing, 3(3), 213-234.

Schmidt, U. (2005). “‘The Scars of Ravensbrück’: Medical Experiments and British War Crimes Policy, 1945-150”, German History, 23(1), 20-49).

Sebag-Montefiore, H. (2000). Enigma: The Battle for the Code.

Singh, S. (1999) The Code Book. New York: Doubleday.

Sowińska, H. (2005). “Life’s Enigma”. In: J.S. Ciechanowski, J. Garbowski, E. Maresch, H. Piechocka-Lipka, H. Sowińska, and J. Sylwestrzak (Eds.), Rejewski: Living with the Enigma Secret (pp. 21-44). Bydgoszcz: Bydgoszcz City Council.

Stripp, A. (1993). “The Engima Machine: Its mechanism and use”. In: F. H. Hinsley and A. Stripp (Eds.), Codebreakers: The Inside Story of Bletchley Park (pp. 83-88). Oxford: Oxford University Press. 

Turing, D. (2015). Prof: Alan Turing Decoded. Gloucestershire: The History Press.

Turing, D. (2018a). “Finally remembered: the Polish codebreaker key to Bletchley Park cracking Enigma”, iNews: The Essential Daily Briefing. Last accessed 11th July 2019. Available at: <>

Turing, D. (2018b). X, Y & Z: The Real Story of How Enigma Was Broken. Gloucestershire: The History Press.

Winston, G. (2016). “Polish codebreakers cracked Enigma in 1932, before Alan Turing”, War History Online, 30th May 2016. Last accessed 11th July 2019. Available at: <>

Woytak, R.A. (1982). “A conversation with Marian Rejewski”, Cryptologia, 6(1), 50-60.


These Enigma episodes have been supported by the Economic and Social Research Council, or ESRC, as part of their annual Festival of Social Science. This Festival celebrates the amazing research and advancements of our best and brightest scientists, and this year, almost five hundred events are happening all over the country from Saturday the 02nd to Saturday the 09th of November, 2019. You can check out the official hashtag #ESRCFestival on Twitter, and you might even find that some of the events are in the news.

Case S01E15 – Enigma, part 3 of 3.

As we reach this final episode, we have covered twenty-one long, tense years, starting in 1918 with the end of the First World War, and picking back up now at the end of 1938. In that time we have seen Marian Rejewski repeatedly break the unbreakable in his small laboratories in Poland. We have watched Hans-Thilo Schmidt sell secrets out of the very safe of the German Enigma office in Berlin to the French Secret Service. And we have watched Alan Turing complete his studies at school in Dorset, at King’s in Cambridge, at Princeton in New Jersey, in the US. But as the intervening two decades have passed by, slowly, Germany has been regrouping, recovering, amassing behind a new figurehead in the form of one Adolf Hitler. This modern young leader spoke a stirring, populist language that fired the imagination and inspired devotion. The timing of such rhetoric was crucial. Germany was smarting, downtrodden, and still suffering financially and diplomatically from a gruelling loss twenty years earlier. They did not merely deserve better, Hitler argued. They were better. They stood above other countries. Their place was at the pinnacle of all civilisation, with other, lesser countries and races below them. To a starving, demoralised populace who had now spent twenty years in global disgrace, such words were very sweet. Almost inevitably, the country turned to him at their bleakest moment, and Adolf Hitler was only too ready to answer.


Welcome to en clair, an archive of forensic linguistics, literary detection, and language mysteries. You can find case notes about this episode, including credits, acknowledgements, and links to further reading at the blog. The web address is given at the end of this episode. And, if you get a moment, leave us a rating wherever you get your podcasts from.

Bletchley Park

Bletchley Park is an enormous nineteenth-century Tudor-Gothic Dutch Baroque mansion in Milton Keynes, about 50 miles or so northwest of London. As you might expect of a mansion that had been built to live in, it had a library, a dining room, and a ballroom (Turing, 2015: 117), and in 1939, in absolute secrecy, the Government Code & Cypher School, GCCS, moved in.

Bletchley Park

Bletchley Park Mansion

The acting head of GCCS at the time was Commander Alexander “Alastair” Guthrie Denniston – a Scottish codebreaker who had originated from Room 40 (I’ll come back to that in a second) and a keen field hockey player. He had been promoted to the operational head in 1919, and ended up remaining in the role until 1942. At Bletchley Park, he had a ground-floor office directly under the dome, and overlooking the beautiful sculpted gardens (Singh, 1999: 162; Turing, 2015: 116).

Commander Alexander “Alastair” Guthrie Denniston

Commander Alexander “Alastair” Guthrie Denniston

So what was this Room 40 business? Well, this is some of the pre-history of British cryptanalysis. Room 40 had its roots in World War I, and came into being in late 1914 as a new section of the British Admiralty. Located, as its name suggests, in Room 40, in the Old Building, the group based there intercepted and decoded some 15,000 or so German messages – a line of work generally described as Signals Intelligence, or SIGINT. SIGINT contrasts with other forms of intelligence gathering such as HUMINT – human intelligence, OSINT – open source intelligence, IMINT – image intelligence, GEOINT – you get the idea. One of Room 40’s most famous SIGINT cases, the Zimmerman Telegraph, will doubtless end up a future case in its own right on this podcast, but suffice to say, they had pedigree and expertise.

Five years later, the Admiralty’s Room 40 was merged with the British Army’s intelligence unit, MI1, and together these now formed the Government Code & Cypher School, or GCCS, just in time for World War II. Room 40, and then GCCS, had historically recruited and continued to recruit predominantly linguists and classicists from the likes of Oxford and Cambridge, and, unsurprisingly for the time, most of these were young men. However, some women who graduated from Newnham College and Girton College were also recruited (Singh, 1999: 161). In fact, it’s worth knowing that most of the 10,000 people who worked at Bletchley Park during the war were women. Unfortunately, given both the secrecy of the place in general and the trend of women being quietly airbrushed out of history, we don’t know much at all about most of the women of that era. One cryptanalyst we do know of was Charlotte Elizabeth Webb, later Vine-Stevens, more fondly referred to as Betty. At just eighteen years old, in 1941 she was invited for a mystery interview conducted entirely in German – a language she happened to be fluent in. At the end of the interview she was handed a travel warrant to go directly the Bletchley Park, given the Official Secrets Act to sign, and immediately given the task of translating intercepted German and Japanese messages. Later, she would go on to work at the Pentagon in the US, and to the delight of people like me everywhere, she wrote a book about her wartime activities, entitled Secret Postings. You can find other women who worked on Enigma by going to and searching the Roll of Honour for women who worked on Enigma in Hut 8. You should get around twelve results.

Anyway, I’m getting a little ahead of myself. The enormous Bletchley Park became the headquarters of the Government Code & Cypher School (GC&CS) in 1939, and most importantly, it provided far more space than the personnel of Room 40 required when they first arrived – a crucial detail in light of the imminent war and the inevitable increase in staff that this would trigger (Singh, 1999: 161).

Bletchley Park grounds

Bletchley Park grounds

Indeed, the expansion not only happened, soon the number of personnel spilled out of the walls of the giant mansion into its outbuildings. Within months, even these were full and wooden huts were hastily erected across the grounds.

Bletchley Park Code-breaking Huts

Bletchley Park code-breaking huts

Each hut was the home of a particular sub-unit focusing on particular codebreaking activities. Hut 6, for example, was focused on decrypting German army and air-force military Enigma communications. These were then passed to Hut 3, where the messages were translated and the information was acted upon (ibid.). Meanwhile, Turing would go on to lead Hut 8, which was focused on decrypting German naval Enigma communications. These decrypted messages in turn were passed onto Hut 4 for translation. As this arrangement suggests, the Enigma used by the army and air-force was not the same as that used by the navy. The naval Enigma was, in fact, more secure and therefore that much harder to break.

So as Bletchley Park was gradually turning into a top secret codebreaking supercentre, what was Turing up to all this time?

Alan Turing

Alan Turing

Well, at some point in 1938, he formally signed up to work for the Foreign Office. Although partial records make it difficult to discern exactly when he was first approached about this work, it seems several people from King’s College had also been approached between 1937 and 1938 by the head of GCCS, Commander Denniston (Turing, 2015: 108-9). At some other point, too, Turing attended a GCCS cryptology course in London near St James’s Park. And somewhere in the vague, secretive mists of these crucial months, Turing would end up at Bletchley Park, assigned to Hut 8, and in charge of cracking the naval Enigma cipher. But now we have to leave the quiet green parks of Bletchley for a while, because, across Europe, events are beginning to spin out of control.


As 1938 began to draw to a close, the Germans utterly crushed all the advances made by the Polish Biuro Szyfrów in one ghastly move. They updated the number of scramblers in the Enigma machine from three to five. The number of distinct arrangements of the scramblers accordingly rose a full order of magnitude, from 6 to 60 (Singh, 1999: 157; Sebag-Montefiore, 2000: 43). But this wasn’t all. They also increased the number of plugboard cablings from six to ten, which meant that the numbers of swapped letters rose from 12 to 20. The number of possible keys went from ten quadrillion to 159 quintillion. That’s 159 followed eighteen zeroes (Singh, 1999: 157). Enigma was still not unbreakable, technically speaking, but the number of bombes the Biuro would have to create to deal with the increase in possible keys was fifteen times greater than their annual budget. Likewise, the perforated cards were a nice idea, on, well, paper, but in practice, they were extremely labour intensive and time consuming to produce (ibid.). After three months they had only been able to create a third of the cards required for Enigma machines with three scramblers. At the same pace, it would take literally years just to get to the same incomplete point for Enigma machines with five scramblers.

In the end, the Poles were defeated not by any lack of ability, as Rejewski’s repeated advances in the face of astounding odds so clearly demonstrates. Instead, they were defeated by a lack of funding, a shortage of equipment, and, ultimately, the political and military situation. Enigma was a mechanical cipher, and to keep up with its ever growing scale and scope, it had to be tackled mechanically. Yes, mathematical skill was utterly crucial, but so too, now, was substantial technological resource. The Poles had the former. Indeed, for a while there, it seems that they had the finest cryptanalyst in the world. But without sheer financial and technological resources, the Poles simply could not bring that priceless intellectual advantage to bear (Sebag-Montefiore, 2000: 44).

As Enigma mutated and became ever more complex, so too did Hitler’s rhetoric become more fervent, more supremacist, more dangerous. He had already begun to step up his anti-Polish vitriol and it was clear even to denialists that an invasion of Poland was on the not-too-distant horizon (Singh, 1999: 158). Major Gwido Langer, overall head of the Biuro Szyfrów and Captain Maksymilian Ciężki (head of the German section of the Biuro) were finally given permission to share all of the details of their progress with the British and the French. The plan was to get the information out of Poland into the hands of the Allies before the invasion began. If, or rather, when the Germans got into Warsaw, they would inevitably tear the Biuro apart looking for any useful information. If the immense progress on Enigma had not already been smuggled out by that point, then the Poles themselves would have to destroy it. Throwing away literally decades of laborious breakthroughs would be devastating, but even that would not be as bad as letting the Germans realise just how far they had been able to crack Enigma. In the hands of the Allies, however, this work could aid in defeating the Germans, and getting them back out of Poland.

Passing the torch

Back in England, at Bletchley Park, British codebreaker Alfred Dillwyn Knox, nicknamed Dilly, had noticed the work being done by Turing, and Dilly soon determined that Turing should be working on breaking German messages encrypted using Enigma (Turing, 2015: 118). Accordingly, Turing worked at this throughout 1939, until, out of the blue, in July of 1939, the cryptanalysts of GCCS were handed a message. The Biuro Szyfrów wanted to hold a trilateral intelligence conference – themselves, British intelligence, and the French Secret Service. They had a vital breakthrough to pass on, but it could only be done face-to-face (Turing, 2015: 119).

From the British contingent, the head of the GCCS, Commander Denniston was to be one of the representatives, and Dilly Knox was to be the other, but apparently the whole affair was deeply annoying to Knox. He had already attended another trilateral meeting with the Poles and the French in Paris in January of 1939, where the French had acted as intermediaries, and that had proven – from the perspective of the British, at least – completely fruitless (2018b: 120-1). He did not anticipate this to be any more productive, and worse, it was that much closer to the border of Germany, which was on the knife-edge of a massive invasion into the very country to which he was now about to travel.

Business, however, was business, and never more so than during wartime, so on an otherwise unremarkable Tuesday the 25th and Wednesday the 26th of July 1939, representatives of the British, French, and Polish intelligence agencies gathered in a secret forest location in Pyry, just to the south of Warsaw (Rejewski, 1981: 227). On the first day, the conference opening was marked by “characteristic Polish military formality” (Turing 2018: 120-1), which apparently vexed and wearied the British. In actuality, this sort of formality is not confined to the military. Across Polish tradition, dressing up in one’s finest clothes and adhering to solemn traditions is a symbolic acknowledgement of the importance of a given occasion, whether that’s a private Christmas Day celebration or a top-secret codebreaking conference. The Polish were, in fact, trying to give due reverence to the proceedings and to their guests, but as can so easily happen in intercultural gatherings, the intention seems to have been entirely misconstrued. Dilly Knox, for instance, was supposedly convinced that such a show was nothing more than a compensatory tactic by the Poles who had actually somehow lied or exaggerated about the achievements of their mathematicians. On the ride home in the car from that first day’s ceremonies, Knox supposedly exploded into an extended rant.

In another account, this was described a tantrum motivated by even less admirable feeling still. Dilly was, according to Gordon Corera’s 2014 account of the matter, incensed that the Poles had beaten him to the solution. Whatever the real cause of Knox’s feelings that day, the next morning when he met the team of mathematicians, he was by all accounts a great deal calmer.

Probably oblivious to Dilly’s feelings on the matter, the Poles proceeded with their big reveal, and handed over all of the information they had. As part of this, they agreed to provide the then deputy-head, soon-to-be-Chief of MI6, Colonel Stewart Menzies, with two replica military Enigma machines that they had made (Turing, 2015: 119). MI6, for those outside of the UK, is the British foreign secret intelligence service, famously portrayed as the agency of James Bond, codename: 007.

Anyway, the Poles carefully explained how the Bomba Kryptologiczna worked and the principles that underpinned it. This was the ticking bombe that you may remember from the previous episode. And what did the Poles get in return? As Rejewski notes:

We learned nothing from our guests. Neither the British nor the French had managed to get past the first difficulties. They did not have the drum connections. They had no methods whatsoever. (Rejewski, 1981: 228)

By the time he had arrived back in Bletchley Park, Dilly Knox seems to have genuinely valued their achievement. Upon his return to England, he sent them a thank you note in a mixture of French and broken Polish, along with a gift: a silk scarf printed with a picture of a horse winning a race. This was intended to signify his acknowledgement that the Poles had indeed beaten him to the solution (Turing 2018).

Whatever the veracity of this charming little vignette, the crucial underlying fact is that the Poles had not merely made progress. They had, as far as we know, made all the significant progress, singlehandedly, that had been achieved by any of the three intelligence agencies. And I specifically include here Turing, who had been working on Enigma for months by this point. But more than this, they were handing it all over, in a single, giant gift, to the French and the British. And days after the conference, as promised, they dispatched one of their replicas of the military version of Enigma to England. It arrived safe and sound in Victoria Station in the middle of August of 1939 (ibid.).

Polish replica Enigma machine

Polish replica Enigma machine

And not a moment too soon.

Two weeks after this, on Friday the 01st of September 1939, Germany invaded Poland, triggering the start of World War II.


War. Another war. For far too many, the horrors and losses and devastation of the First World War only twenty years earlier were still fresh in mind, and now, here they were, marching into a Second World War. As the awful news was announced across the airwaves of England on the Friday evening, Turing was already packing, and on Monday the 04th of September 1939, he moved into the Crown Inn at Shenley Brook End. This was just over three miles away from Bletchley Park and, forgoing the use of a car, Turing would cycle the twenty minutes or so to work and back each day (Singh, 1999: 169).

And now, his work involved understanding, expanding, and capitalising on the treasure trove of breakthroughs that the Poles had handed over. In just one part of this, the Poles had provided careful and detailed descriptions of how the bombes worked (Turing, 2015: 122), but in the process of theorising about and then creating the bombes, their focus had been on simultaneously testing different cyphertext letters at specific positions in the message. Turing, with his gift for envisioning macro-level methods and processes, realised that there was a more general principle underlaying their work, and it was this that he turned his formidable mind upon. Members of Bletchley Park, such as Dilly Knox, had already agreed that relying on the repeated message key would only get them so far. This use key-exchange protocol, and especially its method of repetition, was a glaring weakness in an otherwise meticulous procedure and inevitably, someone, somewhere in the German High Command was going to realise and correct it. As soon as they did so, Rejewski’s method of decryption would become useless (Singh, 1999: 170), and everything the Poles had handed over would turn to ashes. Their concern was well-founded, too. Only eight months later, this key-exchange method would be dropped.

But the principle that Rejewski had worked on, and to such good effect, was sound, and Turing saw in it a greater potential even than Rejewski had. This was not a weakness in the enciphering itself so much as a weakness in the operator. As is sometimes found in the notes from IT helpdesks, the machine was fine. This was a PEBCAK. A problem that existed between chair and keyboard. The user was, and in modern security, intelligence, espionage, and beyond, continues to be, the weak link.

Take randomness, for instance. That primary protection in all good cryptography. Intuitively, we believe that we’re very good at being random, but that’s as far from true as it’s possible to imagine. For a few moments we can spout random streams of words, or pick random numbers, or make random gestures, and then, inevitably, sometimes within seconds, we begin to fall into repetition. Patterns. This is because randomness is cognitively difficult. By contrast, habits are neurologically and psychologically much easier.

Now expand this from the individual to the organisation – literally think of a giant human collective like, say, the military, consisting of no less than three huge entities such as the army, the airforce, and the navy. If trying to wield an entire military across numerous fronts and keep it responsive and up-to-date, randomness in communication is not merely bad, it could cost thousands of lives, or even the whole war. With an increase in numbers of humans and attendant communications, to maintain order and cohesion and understanding, ambiguity must be absolutely obliterated from the system. If the same command is sent to a thousand different units, it is vital that all one thousand units arrive at the same meaning and respond appropriately. It becomes utterly chaotic if ninety-two infer the correct meaning, six are not sure and send back requests for clarification, thus jamming up the comms lines for the rest of the day, and the last four have reached entirely the wrong conclusion but with absolute confidence, never bother to check, and simply go off to do something completely different to they should be doing.

An immediate way to achieve clarity and minimise misunderstandings is to standardise communications – have a very clearly defined system that dictates what words mean, how commands will be given, the way locations will be described, and so on. But standardisations like this means patterns. That is, even more patterns instituted by the organisation to go with the patterns that individuals already fall into because we find randomness difficult. And all these larger and smaller patterns together mean lots of tiny cracks for the cryptanalysts to find, and then wedge crowbars into. It was not mathematics but psychology that led Turing to realise that replicating the three-letter message key would not be the only way in which the German cryptographers were unwittingly making cryptographic mistakes.

In his search for another chink in Enigma’s armour, Turing began reading back over the vast collection of already-decrypted messages, and he soon began to notice other habits. For instance, the Germans invariably sent an encrypted message just after 6am about the weather conditions (Singh, 1999: 170). Any message intercepted at this time was almost guaranteed to include the German word for weather (wetter), and would more than likely be written in an extremely rigidly structured style. So, not only was it reasonable to expect the word wetter in an encrypted message, but it was also likely to occur in a specific location – usually the first six letter of the message proper.

Whenever a correspondence was identified between segments of plaintext and ciphertext, this was referred to as a crib (Turing, 2015: 122). And Turing felt strongly that cribs were the way forward to cracking Enigma without the need for reliance on the repeated message key. Logically, if you know that a particular segment of an encrypted message represents, say, wetter, you can work backwards from this to determine the machine’s settings. In other words, you can ask, what specific settings would transform wetter into the exact string of letters found in your encrypted text?

Unfortunately, the simplest way to do this was also impossible on a practical level (Singh, 1999: 171). You could repeatedly type wetter into an Enigma machine and wait to see if and when the correct string of ciphertext showed up to match the intercepted message in your hand, but this would involve 159 quintillion possible combinations. That’s the 159 with the eighteen zeroes again. If you were to type one per second, continuously, night and day, it would take you trillions of extremely boring years to try every combination, in which time you would die, and the earth would be consumed by the sun’s corona, and the remaining solar system would be torn slowly apart by the ongoing maelstrom of competing galactic forces. Also, the war would be over by that point. So to shorten this process somewhat, Turing instead relied, once more, upon Rejewski’s ideas.

If you remember, Rejewski had figured out a way into Enigma’s secrets by dividing up the individual components of the daily key and tackling them one at a time, before bringing the puzzle pieces back together (Singh, 1999: 171). If Turing were able to find something in the crib he had identified that reflected only the scrambler settings, not the plugboard cablings, he would be drastically reducing his workload, exactly as Rejewski had done.

The solution he landed on was pretty similar to Rejewski’s idea of “chains of letters”, but rather than looking for these within the twice-encrypted message key, which Turing rightly deduced would eventually be dropped by the Germans, he found that he could used the guessed plaintext – that is, these cribs, like wetter – to identify loops in the links between plaintext and cyphertext letters (Singh, 1999: 171-2). But it would still take one replica Enigma machine far too long to test all the possible settings. In a perfect world, the messages needed deciphering within hours, or even minutes, but this is where machines have the advantage over people. If a task will take one machine a thousand hours, then how long will the same task take a thousand machines?

Of course, a thousand machines would be nice, but back in the real world, the GCCS did not have infinitely deep pockets to afford such an extravagant solution, and even if it had, they simply didn’t have the time. This was a race, and every minute was precious. Turing therefore suggested that three replica Enigmas could be wired together in a loop to cycle through the possible permutations of initial scrambler settings. When the correct setting was identified, an electrical current would flow through all three machines and a lightbulb would illuminate (Singh, 1999: 173).

Nevertheless, there was still the problem of the plugboard cablings, which, as you may remember, had increased from six to ten. But here, again, Turing found a solution similar to Rejewski’s. Once the correct scrambler orientations and positions had been identified by the loop of machines, the cryptanalyst could choose a ciphertext that likely had a crib in it, like wetter. They could then type that message into the machine and examine the resulting plaintext especially around the crib word, and this would give them some crucial insights into the letters of the crib that had been swapped (Singh, 1999: 174).

History has it, especially in Hollywood versions like the Imitation Game, that Turing’s solution met with horrified resistance, especially when the probable cost was worked out. Quite how this wrinkle was ironed out, if indeed such a wrinkle existed, we will likely never know, but in the end, Bletchley Park found £100,000 in funding to build the machines. That’s about £6.5 million, or around $8 million in today’s money. For any project, this is a substantial outlay, but to sign off on so much funding for such an untested idea during war when money was already haemorrhaging out of the national coffers, this is an extraordinary mark of trust. Or desperation. Or a lot of both.

The job was entrusted to the British Tabulating Machinery Factory in Letchworth (Singh, 1999: 174), and the chief engineer, Doc Keen, was able to build a machine which would noisily work its way through all 17,576 possible combinations in about twelve minutes (Turing, 2015: 123). And, in homage to the Poles, these machines were named bombes (ibid.).

In his memoirs looking back at this time, Rejewski notes that, once the British at Bletchley Park had access to the information from the Poles, they worked extremely quickly, if for no other reason than that, compared to the Poles, they had far more resources and sixty cryptanalysts at their disposal. After this point, the large majority of keys – eighty three out of every one hundred – would be recovered by Bletchley Park (Rejewksi, 1981: 228). Success, it seemed, might now be on the side of the British.

Or was it?

Poland falls

Back in Poland, on the 01st of September 1939, the German forces had invaded, pouring over Poland’s western border and triggering the start of World War Two. Within days it was an open blood-letting, with the German forces running rampant through the streets.

Marian Rejewski was now 34 years old and he had a wife, Irena, and two children. His youngest was just seven months old – a baby girl called Janina. He urged his family to flee with him to France, but Irena refused, arguing that she would rather stay in Warsaw because the children were too young to cope with the journey.

Basia Różycka, the wife of Rejewski’s colleague Różycki, made the same choice to stay behind with their four-month-old son. Between them they agreed that she would move in with Różycki’s mother in the Polish countryside, but though the decision was made, it could not stop fear and heartbreak. When they said goodbye, Basia recalled how Różycki wept and gave his baby son advice as though he would never see him again (Sebag-Montefiore, 2000: 50).

Back in Warsaw, in a frenzy of secrecy and protection, the Biuro Szyfrów burned every incriminating document, desperate not to give the Germans even the tiniest shred of insight or advantage. The remaining machines that they had not already dispatched went with them as they travelled south to Romania, and they buried other equipment in the ground. They reached the southern Polish border with Romania on the evening of the 17th of September 1939, just as the Soviet Union thundered over Poland’s eastern border in a mass invasion, crushing the country in a devastating military vice.

They were instructed to stay in a refugee camp, and after some debate amongst themselves, overall head of the Biuro Szyfrów, Major Gwido Langer and chief of the German section, Captain Maksymilian Ciężki, both agreed to stay behind, keeping with them the two replica military Enigmas. We cannot know for certain but it makes sense to guess that they were keeping these most precious of possessions hidden until they could organise a safe way of smuggling them out. One can hardly imagine the courage it must have taken to stay behind, closer to the invasions, with such dangerous and incriminating possessions, and in an obvious place to search for such fleeing persons of interest, whilst watching the rest of your friends leave for the probable safety of another country.

In practise, of course, no choice was safe. The rest of the Biuro Szyfrów workers caught a train to Romania’s capital, Bucharest, and once there, they approached the British embassy (Sebag-Montefiore, 2000: 52). But in one of those tiny moments of history that may have deprived Britain of an even earlier and greater success in its fight with Enigma, the British Ambassador told them that he could not promise their safety until he had communicated with London. No. They must wait, and they should come back in a few days’ time.

Such an idea sounded, to the Biuro Szyfrów workers, suicidal. They were employees who had been fleeing with replica Enigma machines, and even though these were now carefully left behind and hidden in a Romanian refugee camp, they were still worth pursuing, capturing, interrogating, torturing, executing. Germany might be a few hundred miles away, but the Soviet Union was not. It bordered directly with Romania. If someone, somewhere, passed on a telegram or made a phone call or dropped into an embassy, soldiers from Germany, or Russia, or both could cross the distance in a matter of hours. Waiting days, therefore, was simply too risky. They must try some other solution.

What of their other international intelligence compatriots? They opted to go to the French embassy (ibid.), and here, their reception could not have been more different. The staff had apparently been expecting their arrival and they were quickly given passports and visas. It took several more tense, secretive days, but Major Bertrand was finally able to bring fifteen employees, including his assistant, the Chief of the Biuro, and the three mathematicians, Zygalski, Różycki, and Rejewski, to France by the beginning of October 1939 (Sebag-Montefiore, 2000: 52). And, only a short while later, he was able to get Major Langer, Captain Ciężki, and their vital replica military Enigmas also into France too (ibid.).

The French were not slow to take advantage of this unexpected, extraordinary boon. In one swoop, they found themselves in possession of both one of the finest teams of cryptanalysts in the world, and of their two military Enigma replicas. Added to this, the displaced Biuro Szyfrów workers were more motivated than they ever had been before to crack Enigma and categorically turn the tide of war. Many of them had just left behind family, wives, children, babies in a country that was being torn apart by two invading armies.

In vain, the British requested the services of the Polish cryptologists, but Bertrand, France, was not sharing this newfound crack team of codebreakers. In no uncertain terms, Bertrand made it clear that Rejewski, Zygalski, and Różycki would not be permitted to work for the British or to travel to the UK. Instead, they were to remain with the Polish army-in-exile in France (Sebag-Montefiore, 2000: 54). Accordingly, a Biuro Szyfrów workshop was created in Vignolles, approximately 40km from Paris, and there the Poles were encouraged to continue their work on Enigma (Rejewski, 1981: 228).

This might sound mean-spirited or even unpleasant of Bertrand, but it’s vital to also remember the context of the war at the time. Germany was delivering a staggering victory over Poland, the country on its eastern borders, within weeks, and the Soviet Union was heavily assisting. Who was on Germany’s western borders? France. And now, all at once, the possibility of an invasion onto French soil had become a probability. Indeed, maybe even a certainty. Bertrand wasn’t being intellectually selfish or plain greedy. He was throwing every possible defence he had between his country, and the seemingly unstoppable German military.

Victory and Agnes

Back in England, in the sleepy, manicured grounds of Bletchley Park, the bombes were under construction. But Turing and his team were not sitting by, idly waiting for their completion. Just like the Poles, they had recognised the flaws of relying on mechanical solutions, and seen the virtues of creating their own Zygalski sheets. However, unlike the Poles, they had the resources to work on punching the holes mechanically, thereby speeding up the process of creating them substantially (Turing, 2015: 124). Indeed, at some point in January of 1940, Turing travelled to France and paid the Polish team a visit to discuss the mathematical logic underpinning the Poles’ success with Enigma thus far. He also brought with him a set of 1,560 Zygalski sheets. These, he explained, were still being used by the British, since through them they were again able to read German Enigma messages (Turing, 2015: 124; see also Turing, 2018b).

Three months later, on the 14th of March 1940, the first prototype bombe was delivered to Bletchley Park on and in a classic over-exuberance of naming, it was, rather prematurely, named Victory.  Unfortunately, Victory proved to be less victorious, more laborious. It was slow and inefficient and essentially near enough useless, other than as a learning exercise. Luckily, the Bletchley Park team also had on hand another exceptionally talented Cambridge graduate by the name of Gordon Welchman (Turing, 2015: 129). Welchman substantially upgraded the design, creating a so-called “diagonal board”, which, in yet another misnaming incident, happened to be neither diagonal, nor a board (Turing, 2015: 129). More important that its name, however, was its purpose, and its job was to speed up the process of checking possible configurations. Just as the machine design was upgraded and submitted, the Germans too upgraded their key-exchange protocol. This, as you will know only too well by now, was their method of repeating the message key twice at the start of the message. As Turing ad predicted, someone had finally recognised the highly problematic nature of this approach, and on the 01st of May 1940, the practice ceased (Singh, 1999: 176).

Ten days later, on the 10th of May, Germany invaded France. Scrambling to protect his valuable assets, Major Bertrand arranged for Rejewski, Zygalski, and Różycki to be evacuated to Paris on the 13th and 14th of May, and there they remained until autumn. Finally, they returned to an unoccupied area of France, but it made little difference now where they were. The Germans had finally begun to perfect their methods of encryption, to the extent that any serious efforts at breaking the cipher now absolutely required substantial mechanical support. In turn, France was fighting an advancing war on its own soil – one that would quickly turn even more bitter as Italy too crossed the Alps and began to attack from the north-east. Entangled in such desperate straits, France could not provide stability, resources, or even safety. In one move, two of the three forces arrayed against Enigma were neutralised. Not only were the Poles now frustrated in their efforts, so too were the French (Rejewski, 1981: 229). The development of ever more complex bombes, which would decrypt German messages using different methods, was now left entirely to the British at Bletchley Park.

The fall of France took six weeks, ending on the 25th of June, 1940. Around five weeks after this, on the 08th of August 1940, the second version of the machine arrived in Bletchley Park (Mollin, 2005: 92; Sebag-Montefiore, 2000: 57). Formally named Agnus Dei, but affectionately nicknamed Agnes, this new machine was precisely what Turing had had in mind.

Agnus Dei, affectionately known as Agnes

Agnus Dei, affectionately known as Agnes

Within two years, there would eighteen bombes hard at work cracking Enigma communications night and day (Mollin, 2005: 92). But the Germans had not yet finished perfecting Enigma, and they were about to make it even harder still.


As I’ve mentioned briefly before, the German army and airforce used one form of Enigma, and the navy used another. A much more secure version. Whilst the army and airforce had upgraded to five scramblers that could be arranged in sixty different positions, the Naval Enigma operators were using eight, and these could be arranged in 336 different positions. This starts to make the old version of Enigma with its three scramblers and their six positions seem rather quaint, right?

Even with Turing’s new machines, the problem was not trivial. Agnes had been able to figure out the settings for an army or airforce Enigma message enciphered through just five scramblers within minutes. But for a naval Enigma message with its eight scramblers, Agnes could spend as long as eighty hours trying to find the right settings (Turing, 2015: 131). This was devastating. The timeliness of the intercepted messages was paramount, and with just one machine tied up for as many as four days, it meant that all other intercepted messages received in the meantime would have to be attempted by hand or just given up on.

But there was more. Operators of the Naval Enigma were extremely careful not to send out stereotypical messages (Singh, 1999: 182), such as rigidly structured weather reports. This made it much more difficult for cryptanalysts to work out cribs. They were essentially cryptographers who were well-versed in the dark art of cryptanalysis, and these would prove to be Turing’s ultimate test.

To help crack the naval Enigma, Turing came up with the idea of a sequential statistical technique based on Bayesian theory. Without going into too much detail, this process involved probabilistically ruling out particular scrambler settings and reducing the amount of time the bombe would need to test the remaining settings. He named this process Banburismus, and developed a “Banbury sheet” which was similar in design to the Zygalski sheets (Turing, 2015: 132-3). In addition, Turing was able to deduce the new message key settings based on information that had been passed to him by the Poles during their meeting in Warsaw in July of 1939 (Sebag-Montefiore, 2000: 71). Even in their absence, the work of the Poles continued to be instrumental in helping the British codebreaking efforts.

However, whilst the combined power of Banburismus and cribbing reduced the cryptanalysts’ workloads, this was not enough to defeat the Naval Enigma (Sebag-Montefiore, 2000: 71).

Without cribs, [the British] could not break any Enigma messages. If they could not break some Enigma messages, they would not be able to identify any cribs. The only other way to read Enigma, as was acknowledged by Turing and his colleagues, was if settings were “captured from a submarine”. (Sebag-Montefiore, 2000: 72)

The decryption blackout was devastating. In the Battle of the Atlantic, one of the most complex and bloody naval wars in history, German U-boat attacks were routing Allied ships that were trying to send across food and arms supplies (Singh, 1999: 182). Without access to German naval communications, Allied ships had no idea where the U-boats were located and were unable to plan a safe path through the waters (ibid.). And without food and arms, the UK was increasingly vulnerable.

For a brief window from the 22nd to the 27th of April 1940, the Bletchley Park cryptanalysts were able to read German naval communications, but only after days of work (Sebag-Montefiore, 2000: 76). One German message intercepted on the 23rd of April and was finally cracked and read at Bletchley Park eighteen days later on the 11th of May. The time it took to read the messages meant that the information they gleaned was too out-of-date to be operationally useful, but, crucially, there was still something that the cryptanalysts could learned from them. These decryptions gave Turing the way into the Naval Enigma that he had been working towards (Sebag-Montefiore, 2000: 76). Turing was eventually able to use Banburismus – his sequential statistical procedure – to break another three days’ worth of naval Enigma messages: the 14th of April, the 08th of May, and the 26th of June 1940. Every one of these was a staggering success, but after their expansive ability to read the army and airforce Enigma messages, it must have felt like pitiful progress.

Many different strategies were attempted to find a way into the Naval Enigma, and each had varying degrees of success, but ultimately, the one which proved most comprehensively and completely successful was theft. Like the breakthroughs of the Poles, which Rejewski himself acknowledged would not have been possible without the documents stolen by Hans-Thilo Schmidt (Rejewksi, 1981: 221), cracking Enigma at Bletchley Park came down to the acquisition of German naval codebooks (Singh, 1999: 184). In March, May, and June of 1941, several German ships were captured and naval codebooks retrieved, along with an Enigma machine. With these, those entire months of communications were effectively transparent to the British.

A German codebook of Enigma settings

A German codebook of Enigma settings

As the successes and setbacks at Bletchley Park began to shape the progress of the war, the work done by GCCS would start to be called Ultra. This name arose from the fact that the SIGINT – the signals intelligence – derived from the decrypted intercepts was considered to be even more confidential that the highest level of security clearance then used by British intelligence. At the time, the top level was Most Secret. It’s amusing to wonder if the lower levels were informally known as Somewhat Secret and Not Really Secret At All, but I digress. Ultra was effectively both an entire massive wartime SIGINT operation, and a new higher security classification.

Of course, it would not have been advisable to reveal such breakthroughs to the German High Command. If they were aware that Enigma was being even intermittently cracked, let alone rendered entirely ineffective for whole months at a time, they would certainly have introduced yet more changes to their encryption, thus leaving the Allies in another lengthy information blackout (Singh, 1999: 184). As a result, to prevent even a suspicion that they were in any way making progress, the British took several precautions to seem less well-informed than they really were. One obvious approach was to sink the ships from which the codebooks had been stolen. Another was to allow some German U-boats to escape even when they knew the boats’ locations (ibid.). But the solution I find most remarkable looks like it might even be the inspiration for James Bond, 007.

Bletchley Park’s SIGINT work was, unsurprisingly, of immense interest to the other Allied forces, and the name Ultra started to be used across the intelligence networks for all SIGINT work of the same nature. But this enthusiastic uptake of that name posed a serious problem. The more Ultra was used, the more likely it was that the existence and scope of Bletchley Park’s work would be inadvertently revealed to the Axis countries. To cover their tracks, British intelligence assigned Ultra the cryptonym – that is, the codename – Boniface, and then they began to communicate about Boniface as though this were a person. Not just any person. An MI6 agent, and master of espionage. MI6, for those not in possession of encyclopaedic knowledge about the history of British intelligence, is the outward-facing, international intelligence agency, as opposed to MI5 which is the inward-facing, domestic intelligence agency.

In this elaborate fiction, Boniface – who I imagine as looking a lot like Neo from the Matrix but you can choose your own stand-in – anyway, Boniface controlled a network of spies. This network was entirely imaginary, of course, but this constellation of non-existence agents was the most crucial part of the cover. Every time the Allies acted upon decrypted intelligence, they risked alerting the Germans to the fact that they had cracked Enigma, but Boniface and his invisible operatives were a perfect cover. When something occurred to rouse the suspicion of the German High Command, they had a troubling accusation to make. Had the British really cracked Enigma, the most advanced mechanical cipher ever created, with its quintillion of settings? Or had a spy from the Boniface network happened upon a crucial detail, infiltrated a secret location, seduced a foolish official? Of the two, which was more believable? And, perhaps more humanly, which was it easier to believe? The possibility that Enigma could have been compromised would be such a unilaterally devastating blow, whereas a spy getting lucky was unfortunate, but it wasn’t necessarily going to happen again.

Whatever the decisions made behind the scenes, Boniface meant that the Axis powers wasted unknown amounts of time and energy chasing after non-existent secret agents, and it kept the decryption of Enigma safely under wraps.


From here, there is surprisingly little Enigma story left to tell. For their efforts thus far in aiding the war, Alan Turing and Gordon Welchman, the fellow cryptanalyst who designed the diagonal boards, were each given cheques for £200. That’s about £10,000 in today’s money, so it was certainly not small beans. The Prime Minister Winston Churchill also visited Bletchley Park on the 06th of September 1941 (Turing, 2015: 139), and subsequent events suggest that he was sufficiently impressed with Turing’s work. Indeed, some while later when Turing, Welchman, and another colleague, Stuart Milner-Barry wanted more staff, they went above Commander Denniston’s head and delivered a letter directly to the Prime Minister making this request (Turing, 2015: 140-1).

In that same year, 1941, Turing also proposed to Joan Clarke, another cryptanalyst and mathematician working alongside him in Hut 8. Clarke accepted the proposal, and when he revealed his homosexuality, she was apparently unconcerned. However, for reasons with which we will likely never be fully acquainted, Turing seems to have ended the engagement.

But the Naval Enigma, which had already posed so many challenges, was about to pose yet more. The first iteration of Naval Enigma, known by the Germans as Hydra, and rather less dauntingly by the British as Dolphin, was dropped by German U-boats in the Atlantic and the Mediterranean. On the 05th of October, 1941, as German fears about potential security compromises began to mount, they switched to Triton, known by the British as Shark, M3. And on the 01st of February 1942, the Germans upgraded to Triton M4, making yet more changes to their encryption processes. This plunged Bletchley Park into another SIGINT blackout.

Enigma Triton M4 with eight rotors

Enigma Triton M4 with eight rotors

The problem, as with so much of modern computing, was effectively reduced to a single issue. Increasing the complexity of the Enigma code was relatively straightforward. One merely need add another scrambler, or more plugboard wires. This multiplied the potential starting settings exponentially. In turn, the bombes would have to work exponentially more hours. A one-hour job would become ten hours, then a hundred. And there was only one realistic solution. They couldn’t uncomplicate the cipher. All they could do was process it more quickly so that the increase in complexity was neutralised. The focus at Bletchley Park now was on how to develop the bombe technology so that it worked at a much higher speed (Turing, 2015: 143).

On the 30th of October 1942, just days before Turing departed for New York to cooperate with the Americans (Turing, 2015: 162), in the early hours of the morning, the German submarine U-559 was spotted around seventy miles north of the Nile Delta. A destroyer group of British ships spent sixteen gruelling hours searching and depth-charging, until finally the damaged submarine was forced to the surface. The German crew who abandoned it failed to destroy the onboard Enigma machine and its codebooks, and also failed to open all the sea-vents and scuttle the craft properly. This meant that, though the submarine was sinking, it was only going down slowly at first, and this allowed enough time for three Royal Navy sailors to swim across from their respective ships. One was a canteen assistant by the name of Thomas William Brown. Aged just sixteen, or possibly even fifteen, since only his year of birth is known, Tommy Brown had lied about his age to join the Navy early. At the time, conscription laws applied to all men aged eighteen to forty-one, though seventeen-year-olds could sign up with their parent’s permission.

Canteen assistant Tommy Brown

Canteen assistant Tommy Brown

Tommy Brown managed to retrieve the Enigma machine and its codebooks from the submarine. More impressively still, unaware of their extraordinary significance, nor of the impact that his actions of the next few minutes were going to have on the entire war, he managed to swim through open seawater, down swells and over waves, dragging the 12kg monstrosity along with him, all the way back to his own ship, where he and it were hauled back aboard.

The other two sailors, Lieutenant Anthony Fasson and Able Seaman Colin Grazier, were still searching the submarine when it foundered, and unable to escape, both drowned. The machine and the materials that these three sailors were able to capture were priceless beyond measure, and in Turing’s absence, they ended the Enigma intelligence blackout (Turing, 2015: 162). As a result of this, when Turing finally returned from the US to Bletchley Park in the spring of 1943, the Battle of the Atlantic had mostly been won.

Fates and fortunes

The war will not end for another two years from this point in the story, and yet, already, the fates of some of the people we have met are about to catch up with them. I wish I could say that each person met the outcome they had earned, but the most awful truth that war reveals is how desperately unfair our fortunes can ultimately be.

Exactly as Turing was heading to New York, on the 08th of November 1942, the Germans moved into Vichy in France where the Poles had been carrying on their work. They were quickly evacuated, and then, after some planning, they were organised into small groups and instructed to travel over the Pyrenees into Spain, and then continue onto the UK. Unfortunately, several of the men, including Major Ciężki, the head of the German section of the Biuro Szyfrów were captured. Meanwhile, one of the three Polish mathematicians, Jerzy Różycki, who had wept when he left behind his infant son, was travelling back after a brief period in Algeria. He was killed when the French passenger ship he was on sank (Rejewksi, 1981: 229).

Fate of Hans-Thilo and Rudolf Schmidt

As the Germans took up occupation of parts of France, the Nazi Party’s secret police, the Gestapo, began interrogating the local populations, and in the course of their investigations, they found a German citizen by the name of Rodolphe Lemoine. His real name was Rudolf Stallmann, and if you have an extraordinary memory, you will remember him as Rex.

Rudolf Stallmann, aka Rodolphe Lemoine, aka Rex

Rudolf Stallmann, aka Rudolphe Lemoine, aka Rex

He was the French agent who had been assigned to Hans-Thilo Schmidt. Rex handed over names and information, and on the 01st of April 1943, Schmidt was arrested by the Gestapo.

This had immediate, wider consequences. Nine days later, on the 10th of April, 1943, his older brother, Rudolf Schmidt, was relieved of his command and had his personal effects searched. This turned up letters in which Rudolf criticised Hitler, the Nazi Party, and the war.

Five months later, some time shortly after the 19th of September, 1943, Hans-Thilo Schmidt’s daughter, Giselle, was asked to come into prison and formally identify his body. According to her account, it seems that Schmidt may have committed suicide, but of course, given the reputation of the Nazi Party and the Gestapo, especially when dealing with spies, it is easy to imagine that another, uglier fate may have befallen him (Turing, 2018b: 280).

A few days after his death, on the 30th of September, 1943, Rudolf Schmidt faced a court martial for his critical letters. Though acquitted, he was not reinstated to his original post.

Four years later, on the 16th of December, 1947, Rudolf Schmidt, now aged sixty, was arrested again, and this time he was imprisoned. Five years later, in 1952, he finally faced a military tribunal and was sentenced to twenty-five years in prison. However, just three years after this, in 1955, now aged sixty-eight, he was released, and died two years later, in 1957, aged seventy.

Fate of Gustave Bertrand

As Schmidt was languishing in a German prison, having successfully crossed the Pyrenees, the two remaining Polish mathematicians, Henryk Zygalski and Marian Rejewski, were themselves languishing in a Spanish prison. After three months, they were liberated by the Polish Red Cross, and taking a laborious detour via Portugal and Gibraltar, finally, on the 03rd of August 1943, they landed on UK soil. Upon arrival, Rejewski and Zygalski became part of a Polish military unit in Boxmoor and began working on breaking yet more German ciphers, but they never received an invitation to work on Enigma at Bletchley Park.

In fact, the precise reason why Rejewski in particular was never recruited to Bletchley Park despite the fact that his work was seminal in decrypting Enigma throughout the earlier stages of the war has long been considered a bit of a mystery (Singh, 1999: 188).

It was always a mystery to me that the Polish contingent was not incorporated at Bletchley during the war, where they would no doubt have made an invaluable contribution; but in fact they were side-tracked in France and had to be evacuated when the Germans overran the whole of the country. I can only assume there were security doubts, and I believe the Poles continued to operate their own organisation; but I feel there must have been a sad waste of resources somewhere. (Stuart Milner-Barry, 1993: 92. WWII codebreaker & head of Hut 6 at Bletchley Park)

Oleksiak (2014) also references the potential security risk of recruiting Rejewski and Zygalski in the UK, noting that they had perhaps not been invited to Bletchley Park because they had been briefly captured on their way to Great Britain. However, Turing (2018b: 143), argues that this apparent unwillingness is a myth: when the Poles were in France, Commander Alastair Denniston had written to then-Captain Gustave Bertrand repeatedly, in several attempts to recruit them to Bletchley Park, but the French had effectively beat them to it and Captain Bertrand was not sharing (Turing, 2018b: 144). But there were other, simpler issues at play. War is a chaotic time and there were hundreds of thousands of displaced people circulating round Europe, trying to find temporary new lives for themselves till they could go back home. When Zygalski and Rejewksi arrived in the UK, Bletchley Park were unaware of the identity of the mathematicians – at least at first. Added to this, the Ultra operation was above Most Secret, and almost no one at all knew what the Poles had done, so extraordinarily few people would have been able to join the dots and send the right sort of message to the right sort of people (2018b: 259).

Even as Rejewski and Zygalski were getting settled into their work in Boxmoor, Major Gustave Bertrand was still in France. He too was captured by the Germans who suggested that he should work for them as a double-agent. Major Bertrand ostensibly agreed, returned to attend a meeting with British intelligence, and promptly vanished into thin air.

Major Gustave Bertrand, French spy

Major Gustave Bertrand, French spy

Just days before the Normandy landings, he reappeared with his wife Mary and a Jesuit priest, climbed into a tiny unnamed aircraft, and flew to the British Isles, finally joining the Poles in Boxmoor in June 1944 (Rejewski, 1981: 229). Bertrand would later go on to write a book detailing his exploits, and this would be one of the most insightful firsthand accounts of the cooperation between the French and Polish and the subsequent cracking of Enigma both before and during the war.

Perhaps aggrieved at the ongoing silence from Bletchley Park, or with newer information from Bertrand, or simply finally motivated by his own irritation, on the 01st October 1944, three months after Major Bertrand’s arrival in Boxmoor, Rejewski later sent a letter of complaint to his superiors in London. He wanted his Polish replica Enigma machine back (Turing, 2018b: 265). By this stage, however, the operation of Bletchley Park had drastically changed. Dilly Knox had passed away in 1943. Alan Turing’s machines were now being operated factory-style, and Turing himself was working somewhere else. So too was Commander Alastair Denniston. There was no one at Bletchley Park who knew the Poles to vouch for how invaluable their work had been in the fight against Enigma (ibid.).

Not quite a year after Rejewski’s aggrieved letter asking for his Enigma machine back, on the 02nd of September 1945, the war came to an end. Major Gwido Langer, the overall head of the Biuro Szyfrów, and Captain Maksymilian Ciężki, head of the German section of the Biuro Szyfrów were freed from prisoner-of-war camps by Allies in 1945.

Fate of Tommy Brown

But what of that young man that we so lately met – Tommy Brown, a child, who dragged an impossibly heavy Enigma machine and all its codebooks from a sinking submarine, across the open sea, back to his ship, and in so doing, turned the course of the war? Only three years later after that incredible event, in 1946, at the age of eighteen, Tommy was on shore-leave and at home with his family. A housefire broke out, and he managed to rescue his sister, Maureen. In so doing, he was badly injured, and days later, those injuries would end his short life.

Fate of Henryk Zygalski

And what of the two remaining Polish mathematicians?

Henryk Zygalski, creator of the invaluable Zygalski sheets, opted to settle in the UK, and became a British citizen in 1949 (Turing, 2018b: 281). Dismayingly, his Polish qualifications were treated as effectively meaningless in the UK, and he was forced to requalify via the Polish University College (ibid.). A report from Imperial College London in 1951 described him, patronisingly, as “capable of originality in Mathematics” (cf. Turing, 2018b: 282). He took English lessons and married a British woman named Bertha Blofield. Eventually he began work as a lecturer in mathematical statistics in Battersea Technical College, which would later become the University of Surrey.

Not long before he passed away, he was awarded an honorary doctorate by the Polish University in Exile. He died on the 30th of August 1978. On the 01st of September 2018, a memorial stone at his grave in Chichester Cemetery was unveiled by the Polish ambassador to the UK (Turing, 2018b).

Fate of Marian Rejewski

And what of the third Polish mathematician, Marian Rejewski, whose incredible intellect cracked Enigma when no one else could even make the first insights? Rejewski chose to return to Poland, and arrived back there on the 21st of November 1946 (Turing, 2018b: 277). Shortly afterwards, in the summer of 1947, Rejewski and his family suffered a tragedy when his 11-year-old son Andrzej died of polio after only five days of illness (Turing, 2018b: 281).

Rejewski was repeatedly investigated throughout his life by the communist secret police. Although he was a source of constant suspicion, they struggled to pin anything on him as he made quite sure he was “wholly uninteresting”. However, the secret police did ensure that he lost his job as a sales supervisor in 1950 (ibid.). He spent most of the rest of his working life as a bookkeeper at the Provincial Union of Labour Cooperatives, until his retirement in 1967. In the same year, Colonel Władysław Kozaczuk published a book entitled Bitwa o Tajemnice (Battle of Secrets) which briefly mentioned the contribution of the Polish mathematicians in cracking Enigma, but it did not name them. This book was in Polish, however, and Poland was still trapped behind the Iron Curtain, so it did not immediately become common knowledge (Turing, 2018b: 279).

After his retirement, Rejewski and his family moved to Warsaw in 1969. The details of his involvement in cracking Enigma did not fully surface until Major Gustave Bertrand published his detailed memoirs in 1972. Again, however, Bertrand did not reveal the mathematicians’ names, but after this, Rejewski stepped forward to reveal his identity. He subsequently rose to prominence, gave television and radio interviews, and wrote several articles detailing the work of himself and his colleagues in Cryptologia (Sowińska, 2005: 41). On the 12th of August 1978, he received the Officer’s Cross of the Order of the Rebirth of Poland from the Polonia Restituta, and in 1979, he received the Silver Cross for Services to the Country’s Defence (Turing, 2018b: 281). The Polish Mathematical Society made an exception to its usual rule of only granting membership to those with PhDs and made Rejewski an honorary member (Lelwic, 2005: 65). Rejewski passed away suddenly in Warsaw on the 13th of February 1980 from a heart attack, and was buried with full military honours in the military cemetery of Powązki (Turing, 2018b: 281; Lelwic, 2005: 65). Rejewski went on to receive several post-humous awards from Poland, the UK, and the US.

Fate of Alan Turing

And finally, what of the fate of the last person in line to mechanise on a massive scale the decrypting of Enigma? What of Alan Turing? Seven years after the end of the war, at around Christmas time in 1952, then-39-year-old Turing had started a relationship with unemployed 19-year-old, Arnold Murray. A few weeks into the New Year, Turing’s flat was burgled, apparently by an associate of Murray’s. When Turing reported the crime to the police, they opened an investigation, and in the course of it, Turing acknowledged that he and Murray were in a relationship. At the time, in UK law, homosexual acts were deemed to violate S11 of the Criminal Law Amendment Act 1885, and both Murray and Turing were charged with gross indecency.

At the end of March 1952, Turing pleaded guilty, and was forced to choose between prison or a procedure sometimes informally known as chemical castration. At the time, this involved the individual being given injections of synthetic oestrogen as a means of suppressing their sex drive. Turing was also barred from the US, lost his security clearance, and was no longer allowed to undertake SIGINT and cryptography work for the Government Communications Headquarters, or GCHQ, the organisation that had emerged from GCCS after the war.

Just fifteen months later, Turing was found dead by his housekeeper, with a half-eaten apple beside his bed. This was never tested, but when his cause of death was subsequently established as cyanide poisoning, the apple was inferred as the most likely medium of ingestion. Debate surrounds the intention behind Turing’s death.

Some speculate that this was misadventure. Turing was, they argued, careless with chemicals and could easily have poisoned himself by accident. Added to this, Turing often ate an apple before bed and regularly only consumed half, his treatment had stopped a year earlier, he had seemed in good spirits before his death, he had made a list of jobs to do for the following week, and perhaps most importantly, the cyanide poisoning looked to be more typical of inhalation than of ingestion. Turing had a gold-plating apparatus that used potassium cyanide set up in his very small spare room, and thus, according to this theory, he could have breathed in a fatal amount.

But, others rejoin, Turing had a long-standing fascination with the scene in Snow White where the Wicked Witch dips the apple in poison, and even if the treatment was now over, Turing was still not able to go to the US or work for GCHQ. And deliberately ordering and placing the gold-plating machine in such a room to give rise to a possible conclusion of death by misadventure is precisely what an extremely intelligent person would have done, thereby allowing his mother to plausibly deny that her son had committed suicide.

Yet another theory is that Turing was becoming, in the view of the secret services, an extraordinarily problematic security risk. He was still undertaking highly classified work for GCHQ, but he was also taking holidays in countries close to the Iron Curtain, and as a practising homosexual, he was open to being entrapped. They need only lure him into, or capture him in, some situation that would be extremely compromising through the lens of British law, and he would be forced to choose between criminal punishments at home or working for and handing intelligence over to a foreign power. Thus, this theory argues, Turing posed a risk that was directly proportionate to his brilliance, and supposedly the only solution in the end was for agents of the state to assassinate him. It’s not one I find especially credible, to be honest, but the truth is, we will probably never know exactly what happened. All we can know now is that Turing was treated extraordinarily badly by the government he had given his utmost to, and on the 12th of June, 1954, he was cremated at Woking Crematorium. His ashes were scattered in the gardens there, as his father’s were before him.

In 2009, after a heavily endorsed petition, the then-Prime Minister Gordon Brown publicly apologised for the way that Turing had been treated, as follows:

Thousands of people have come together to demand justice for Alan Turing and recognition of the appalling way he was treated. While Turing was dealt with under the law of the time and we can’t put the clock back, his treatment was of course utterly unfair and I am pleased to have the chance to say how deeply sorry I and we all are for what happened to him… So on behalf of the British government, and all those who live freely thanks to Alan’s work I am very proud to say: we’re sorry, you deserved so much better.

For the next few years, a battle would rage back and forth through the Houses of Parliament, mainly driven by John Leech, the MP for Manchester, to have Turing pardoned. As a side note I dislike this word anyway since it seems to suggest that Turing would be forgiven for his wrongdoing, when I actually feel like the crime he was convicted for was never a wrongdoing to begin with. I would rather the thing were expunged from his record altogether, and that it is Turing who is asked for his pardon for the mistreatment he received, but I recognise that this is the legal parlance and that even this step is significant. Anyway, after numerous attempts, Leech was finally successful in having the Alan Turing Law passed. This secured pardons for 75,000 other men and women who had been convicted of similar crimes.

And finally, on the 24th of December, 2013, Queen Elizabeth II signed a pardon for Turing’s conviction for “gross indecency”, with immediate effect. Eight months later, in August of 2014, the Queen officially pronounced Turing pardoned.


Some historians have argued that cracking Enigma at Bletchley Park was the key to the Allied victory, but this has not gone uncontested (Singh, 1999: 187). A more conservative, and more widely accepted, interpretation is that cracking Enigma shortened the war, probably by around two years (ibid.), maybe by three at an absolute extreme, and it may have saved as many as fourteen million lives.

Without the intelligence gathered as a result of cracking the Naval Enigma, the Battle of the Atlantic – argued to be the longest and most complex naval battle in history – would have significantly delayed the plans of the Allied forces for the D-Day invasion at Normandy in June of 1944 (Singh, 1999: 187).

But perhaps most problematically, whilst the contribution of Turing has been celebrated, and rightly so, of course, this seems to have been at the expense of the incredible work and breakthroughs achieved by the Poles. Historically their role has been downplayed or ignored entirely in the West. This may have been at least partly owing to the fact that Poland was – until 1989 – on the wrong side of the Iron Curtain (Winston, 2016). Maciej Pisarski, the Deputy Chief of Mission for the Polish Embassy in Washington, has argued that the cooperation between Poland and the UK during the war more generally was not acknowledged once Poland effectively became a communist Soviet satellite state. It would not have fitted the narrative of the time. In addition, in the aftermath of the war the Allies were chiefly concerned with appeasing Stalin, which meant that Poland was, for all intents and purposes, thrown under the bus (ibid.).

In an attempt to raise public awareness of the Polish contribution to cracking Enigma, the city of Poznań and the Polish region of Wielkopolska (Greater Poland) have created a dedicated travelling exhibition entitled Enigma, Decipher Victory. This exhibition has toured several countries, including Canada, the Netherlands, and Belgium. And funding for an Enigma Education Centre to be built in Poznań has been approved.

In Poznań, where the Polish cryptanalysts’ adventure with Enigma began, there is a prism-shaped monument dedicated to Rejewksi, Zygalski, and Rόżycki. The monument, designed by Grażyna Bielska-Kozakiewicz and Mariusz Krzysztof Kozakiewicz and was unveiled on the 75th anniversary of the first Enigma code being broken. It is located outside Poznań Imperial Castle, on the site of the Department of Mathematics where the three men had originally studied:

Polish monument

Finally, for those in the UK or who might one day visit, Bletchley Park itself is now open to the public as a museum. You can walk the same grounds, see the same sights, and even sit in the same rooms where Turing and his team worked. A quick internet search for Bletchley Park should find you all the information you need.

This Enigma miniseries is dedicated to all those who dedicated their best efforts, and even their lives, to ending the war, no matter what nationality, gender, age, rank, or occupation, from junior canteen assistant to chief cryptanalyst. And this is especially dedicated to those who lived in anonymity and obscurity, whose personal silence ensured public safety, whose dedication and work has never been, and will never be celebrated in worldwide Hollywood blockbusters, whose stories have died with them. May we all be wiser and, in looking back, may we learn from our past a peaceful way forward to a better future.

End of part 3 of 3.


This episode of en clair was researched and fact-checked by Rebecca Jagodziński. And it was scripted, narrated, and produced by me, Dr Claire Hardaker. And it was supported by the Economic and Social Research Council as part of their Festival of Social Science. However, this work wouldn’t exist in its current form without the prior effort of many others. You can find acknowledgements and references for those people at the blog. Also there you can find data, links, articles, pictures, older cases, and more besides.

The address for the blog is And you can follow the podcast on Twitter at _enclair. If you like, you can follow Rebecca on Twitter at RjJagodzinski, and you can follow me on Twitter at DrClaireH.