181. The Imitation Game: How Alan Turing Broke Enigma (Ep 1)

A secret mission in the middle of a war to Bletchley Park. One that will lead to the closest intelligence alliance in history. Listen as David and Gordon tell the secret history of how the codebreakers at Bletchley Park worked with their American allies to defeat Hitler. ------------------- THE REST IS CLASSIFIED LIVE 2026 at The Rest Is Fest: Buy your tickets ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ to see David and Gordon live on stage at London’s Southbank Centre on 4 September: ⁠⁠⁠⁠https://www.southbankcentre.co.uk/whats-on/the-rest-is-classified-live/⁠⁠⁠⁠ ------------------- Sign-up for our free newsletter where producer Becki takes you behind the scenes of the show: ⁠⁠⁠⁠⁠⁠⁠https://mailchi.mp/goalhanger.com/tric-free-newsletter-sign⁠-up⁠⁠⁠⁠⁠⁠ ------------------- Join the Declassified Club to go deeper into the world of espionage with exclusive Q&As, interviews with top intelligence insiders, regular livestreams, ad-free listening, early access to episodes and live show tickets, and weekly deep dives into original spy stories. Members also get curated reading lists, special book discounts, prize draws, and access to our private chat community. Just go to ⁠⁠therestisclassified.com⁠ or join on Apple Podcasts. ------------------- Get a 10% discount on business PCs, printers and accessories using the code TRIC10. Visit ⁠⁠⁠⁠https://HP.com/CLASSIFIED⁠⁠⁠⁠ for more information. T&C's apply. ------------------- EXCLUSIVE NordVPN Deal ➼ https://nordvpn.com/restisclassified Upgrade your online protection with an all-in-one security app! It’s risk free with NordVPN’s 30-day money-back guarantee 🌍 ------------------- Email: ⁠⁠⁠⁠⁠[email protected]⁠⁠⁠ Instagram: ⁠⁠⁠⁠⁠⁠⁠⁠@restisclassified⁠ Video Editor: Joe Pettit Social Producer: Emma Jackson Assistant Producer: Alfie Rowe Producer: Becki Hills Head of History: Dom Johnson Exec Producer: Tony Pastor Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:03David McCloskey?

  For exclusive interviews, bonus episodes, ad-free listening, early access to series, first look at live show tickets, a weekly newsletter, and discounted books, join the Declassified Club at therestisclassified.com.

• 0:25David McCloskey?

  A top-secret wartime mission to Bletchley Park, one that will lead to the closest intelligence partnership in history. Well, welcome to The Rest Is Classified. I'm David McCloskey.

• 0:34Gordon Corera?

  And I'm Gordon Corera.

• 0:35David McCloskey?

  And Gordon, this is a very special episode of The Rest Is Classified. Now, I mean, most episodes we do, we should say.

• 0:42Gordon Corera?

  Everything is special.

• 0:42David McCloskey?

  Everything is very special, but this episode in particular is quite special because we are recording it at Bletchley Park.

• 0:50Gordon Corera?

  We are recording it on location.

• 0:52David McCloskey?

  On location.

• 0:53Gordon Corera?

  First time we've done that, and we should say we have also got an audience in front of us.

• 0:58David McCloskey?

  Yes.

• 0:58Gordon Corera?

  Who are members of our Declassified Club. And these are the select few who are fast enough to snap up tickets, which I think sold out in minutes.

• 1:07David McCloskey?

  Seconds.

• 1:08Gordon Corera?

  Seconds.

• 1:10Gordon Corera?

  And they're here to be part of this recording. So as you just heard, you might hear them occasionally with hopefully laughter, maybe a bit of heckling.

• 1:18David McCloskey?

  Screams.

• 1:18Gordon Corera?

  Screams. It's a first for us to do this, isn't it?

• 1:21David McCloskey?

  It is, and it is. It's my first time here. You've been here many times, right, Gordon?

• 1:25Gordon Corera?

  I have. I mean, I've been coming for maybe about 20 years. So one of the shocking things about Bletchley Park is because it was kept secret for so many years, it was nearly shut down and destroyed completely. It nearly became a housing estate, but it was slowly kept going by the work of many volunteers and passionate people. And I remember 2013, when they were doing a big renovation to create what it looks like today, and I was taken around and the floorboards were broken and you'd step on something and it would crunch. And you'd look down and it was the bones of a pigeon which had died and been left in situ.

• 1:58David McCloskey?

  That is not where I thought this story was going.

• 2:00Gordon Corera?

  But that was what it was like back then. And now you can go to it and see it being wonderfully renovated. And it is a fantastic place to visit, as I'm sure you'll see as we go around today.

• 2:10David McCloskey?

  You couldn't have a more Carrera in sign than the bones of a pigeon, could you?

• 2:13Gordon Corera?

  No.

• 2:14David McCloskey?

  Well, I think to some extent, the intelligence partnership between the US and the UK has been a running theme of this podcast, right? So it makes a lot of sense to do a few episodes here in person at a place that perhaps more than any other is kind of core to the founding of that partnership, a partnership which has never been stronger.

• 2:36Gordon Corera?

  It's doing fine at the moment.

• 2:37David McCloskey?

  Which is doing wonderfully fine. And so we're gonna, I mean, I think really over a course of a couple of episodes here, dive into the very beginnings of how this partnership started.

• 2:48Gordon Corera?

  That's right. We're not going to tell the whole Bletchley Park story. We're going to focus particularly on its role, giving birth to the special intelligence relationship between the US and UK. Because as you said, it's an important theme that we've been looking at and which really matters today, I think, as well, and has relevance when you want to understand how tightly bound together, American and British intelligence are. The place to understand where that came from is here at Bletchley Park. And particularly if you go back to one incident at the start of the war.

• 3:24Gordon Corera?

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• 3:26David McCloskey?

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• 3:38Gordon Corera?

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• 3:58David McCloskey?

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• 4:15David McCloskey?

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• 4:32Gordon Corera?

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• 6:28David McCloskey?

  And so, I mean, I guess maybe it makes sense to start the story, like all good stories on this podcast, start with the Americans.

• 6:34Gordon Corera?

  Yes.

• 6:34David McCloskey?

  Let's start there.

• 6:35Gordon Corera?

  Yeah, can't escape them. The Americans are coming.

• 6:39David McCloskey?

  There would be boos and heckling. We prepared everyone. Yeah.

• 6:41Gordon Corera?

  It's already started.

• 6:42David McCloskey?

  It's already started.

• 6:43Gordon Corera?

  But yeah, that's right. It's just after about 10:00 PM on February 8th, 1941, and four Americans are coming up the drive just behind us. They walk up to the front door of the old mansion house. There are blackout curtains to stop any chinks of light emerging, which might allow German bombers to find the place. Earlier in the day, the head of Bletchley Park at the time, Alistair Denniston, had received a phone call to say the packages have arrived in a ship in Kent. Now, the packages were four people and a lot of very sensitive crates of equipment. And Denniston tells his assistant, "There are four Americans who are coming.

• 7:28Gordon Corera?

  I require you to be ready with some sherry."

• 7:33Gordon Corera?

  And that's what they want. "And you're not to tell anybody," he tells his assistant Barbara. And it has been a pretty crazy journey for these Americans to get here to Bletchley Park and nearly ended in disaster, and we'll come to that journey shortly. But it was an amazing mission because it is worth saying that these four Americans are coming in February 1941. And of course, at that time, America is not even in the Second World War yet, is it?

• 7:58David McCloskey?

  Now, the context for the visit, the wartime context, is really important, right? Because, as you say, America's not in the war. Britain is really standing alone and vulnerable. I mean, France and most of the rest of Europe have been conquered by Nazi Germany. British troops have been evacuated from Dunkirk. The country is very isolated, worried about an actual invasion, being strangled at sea by German U-boats. So Britain is looking increasingly to Washington for help with opening supply lines and for a lot of military equipment and technical support that are going to be really critical to winning the war.

• 8:38Gordon Corera?

  So if we go back to June 1940, Winston Churchill gives this very famous speech, "We shall fight them on the beaches." It's a message of defiance, but there is another message to that. It ends with a line that even if Britain is subjugated, the fight will go on until, in God's good time, the new world with all its power and might steps forth to the rescue and liberation of the old. And what he was doing there was very much saying, we are going to need America's help to win this war. And soon after that, you get this discussion of scientific intelligence and technical exchanges

• 9:22Gordon Corera?

  between the US and the UK. And it's important to say here that Britain had the lead on lots of fields in technology, particularly radar. So it's made some of these advances in radar and it's going to start sharing some of these advances with the Americans. And the point is partly to say, we've got something to offer you. The Americans are keen to learn what the Brits are developing and to get hold of that. But the question is, do you do it with code breaking and cryptanalysis?

• 9:53David McCloskey?

  Probably the most sensitive of those technical fields at the time.

• 9:57Gordon Corera?

  And so this is the one which will focus on Bletchley. But the issue for Britain is, do you trust the Americans? Do you trust the Americans?

• 10:07David McCloskey?

  It's really an evergreen question, isn't it?

• 10:09Gordon Corera?

  An evergreen question. Do you trust the Americans to open up with what is your biggest secret, if you're Britain, at the start of the war?

• 10:18David McCloskey?

  And that secret, in many respects, is here at Bletchley.

• 10:22Gordon Corera?

  This is the secret. I mean, this place we're at now is the secret because it is home to Britain's greatest breakthrough. So just to give a bit of context to that, after the First World War, the British government had the Government Code and Cypher School, which sat under MI6, which was its code breaking organisation. And Bletchley had been bought precisely in case of war because they knew they needed a facility outside of London, more secret, which was a kind of fallback place. And so it had been bought by the chief of MI6, allegedly with his own private money in the 1930s.

• 11:01Gordon Corera?

  The crucial thing is code breaking had been changing because in the First World War, it was based around code books and the kinds of people who were code breakers were your classic crossword puzzlers, linguists.

• 11:17David McCloskey?

  They weren't mathematicians.

• 11:18Gordon Corera?

  They weren't mathematicians. But in the early 1920s, in Germany, you get the arrival of a new machine which is called Enigma. And initially, it's interesting because it's actually made commercially and it's sold to banks because it's being offered to banks and businesses who want to communicate securely. But the crucial thing about it is it's an electromechanical machine. You can see them when you come around Bletchley Park here, has what looks like a typewriter keyboard. You press down on a key, an electric current is sent through rotors, which scramble what that letter will turn into. And it lights up on a display, the rotors move every time. Even if you press the same letter again, you'll get a different path for the electrical

• 12:02Gordon Corera?

  current, creating a different output. And you can set it in different ways with different settings for the rotors, creating a huge number of combinations. Some will say 158 million, million, million possible permutations. That's a lot.

• 12:17David McCloskey?

  It's a lot.

• 12:18Gordon Corera?

  That's a lot.

• 12:19David McCloskey?

  And it's being, by the time of the Second World War, it's really the backbone of a lot of the kind of operational communications inside the German military, the Luftwaffe, the SS, I mean, even the Weather Service is using it. So it's not the really high level strategic kind of telexes that are going from the Nazi High Command to the army commands. But in many ways, it's even more valuable because it is the stuff you would want to collect to actually disrupt or go around or target specific U-boats or, you know, German formations as they're massing around Britain.

• 12:59Gordon Corera?

  But it looks like an impossible target. Impossible to go through that number of combinations through brute force, through simply kind of cycling through them all. And it's interesting because the head of the Code and Cypher School in Britain says it would be a waste of time and public money even to try to crack Enigma. But on the eve of war, there's a meeting actually in Poland. And it's very interesting because British, French and Polish spies meet in a forest just outside of Warsaw. And it's the Poles who will reveal to the British and the French that they've made some breakthroughs in cracking versions of the Enigma code.

• 13:40Gordon Corera?

  And what's so important is that they'd realised that it's no good having crossword puzzlers anymore. What you need are mathematicians. And they'd brought in mathematicians who could understand how to bring down the possible range of combinations. And then they'd started to look at how you could then use machines to work through the probabilities. And they'd built something called a Bomber, possibly called that because it made a ticking sound as it worked through different combinations and look for a solution to what the code was. And for the Brits who go over on this mission, this is a kind of moment of revelation. And they start hiring mathematicians.

• 14:22Gordon Corera?

  And of course, the most famous mathematician that they hire at that point is Alan Turing, who will be one of the geniuses who will help build a British version of the Polish Bomber, a more advanced version, which will be called the Bom, and which you can see here at Bletchley Park, and which is going to be used to try and deal with Enigma. The crucial thing is the code made by Enigma looks random, but it's not. It's made by a machine set up in a particular way to generate complexity. I think the best way of understanding it is that however good a device is in theory, the way people use it is often the flaw. And it's a bit like with our passwords for our computers and our online life.

• 15:06David McCloskey?

  They're not random.

• 15:07Gordon Corera?

  They're not random. They're not random. People reuse their passwords. And one of the tricks that Bletchley understood was something called cribs, where you are guessing what is going to be in a message because there's a standardised bit of a message. Maybe it's the fact that they always start or end their message with a particular greeting, or maybe it's that there's a weather report at the start or end or at a particular pace in a message. So you have something which you can use to test through your probabilities and to look for a setting which might give you an answer. And you can then also bring it down through facts like the Enigma machine never encrypted one letter as itself. So if you press E, it will never come out as E.

• 15:49Gordon Corera?

  So if you start to use those two things together, you can start to bring down the probabilities and the number of possible permutations. And then you use these bombs, which are basically a group of Enigma machines. It's like a big box, maybe about six feet tall, and you can see them here at Bletchley, which can work through the combinations. Once it finds a path, then it will light up and show you, you've got a possible match. It's a little bit more complicated than that. I think that what's interesting is it's the mixture of human ingenuity, and Turing is very important in that, but it isn't just Turing because there's, I mean, at its peak

• 16:29Gordon Corera?

  at Bletchley, there's 10,000 people working here, 10,000 people working. And a lot of them are doing some of the work to look for the different patterns which exist. They are filing information, they are collecting the signals. There's a huge amount of what's really early data analysis which is going on by people. So it's much more complicated than just the one genius of Turing, even though he was a genius. There's work on an industrial scale at Bletchley to do this, which involves people and machines working together.

• 17:02David McCloskey?

  So as those Americans are arriving in early 1941, that is the secret essentially of Bletchley Park, is that the Brits are starting to have some real success at breaking Enigma. But there is a significant challenge remaining, isn't there?

• 17:19Gordon Corera?

  Yeah, that's right. I mean, that's the secret, is that by 1940, they are starting to make some breaks into Enigma. First of all, I think with the Luftwaffe, the German air force, the German naval Enigma is a much more challenging proposition.

• 17:35David McCloskey?

  But probably the most valuable to break.

• 17:36Gordon Corera?

  But probably the most valuable because you've got the Battle of the Atlantic, which is so important, and the issue of convoys and supplies. And this is of course, one of Britain's greatest secrets. Because if that secret gets out to the Germans that you are breaking the codes, then they will change their codes, they will change the machines, they will change the way they wire them, they will change the way they use them. So it's at this point, it's a very fragile hold that they've got on elements of Enigma through 1940, which they are nervous about. And that is the secret of Bletchley Park. And that is the question, which is, do you trust the Americans to tell them?

• 18:12David McCloskey?

  And what do the Americans actually bring to the table as they come over to Bletchley Park? So maybe there, let's take a break and when we come back, we will look at those Americans and what they are bringing to Bletchley Park.

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• 20:23Gordon Corera?

  Welcome back. So David, we've looked a bit at the British success at code breaking, the work here at Bletchley in intense secrecy to use the bombs to try and crack the Enigma code. What about the Americans? How good are they at code breaking?

• 20:42David McCloskey?

  Well, I guess the bottom line is that maybe not quite as good as the Brits at this time, which pains me to say, but it is probably worth going back a bit to set up the context behind American code breaking as we get toward Bletchley. So the mission at the time will be known as the Sinkoff mission.

• 21:01Gordon Corera?

  That's the one that comes here in February 1941.

• 21:03David McCloskey?

  Led by Abraham Sinkoff. Now, a decade earlier in 1930, Sinkoff had been introduced to code breaking by William Friedman. Friedman himself is a very fascinating character. He's this kind of flamboyant son of a Hungarian Russian Jewish immigrant. And Friedman had taken charge of this very tiny unit inside the army called the Signal Intelligence Service. And he has three young recruits that he brings in with him. Sinkoff is one of them. Another one, Solomon Kolback, they're close friends, classmates from Brooklyn. There's another guy named Frank Rowlett. They're all mathematicians, so they're not the crossword puzzlers of old.

• 21:41David McCloskey?

  In 1930, Friedman takes his proteges and shows them a secret, really one of the kind of crown jewels of American code breaking at the time. Friedman takes them down the stairs, second floor of what's called the munitions building, goes into this deserted corridor, stops outside and then pulls out a small card from his coat pocket and it has a combination. He opens a combination lock on the front of the steel door, swings the bolt open behind it's yet another steel door. It's an older version of a SCIF. And inside the room is pitch black. Friedman turns the light on.

• 22:24David McCloskey?

  Everything in the room is completely dusty, covered in dust. And Friedman turns to his proteges and says, "Welcome, gentlemen, to the secret archives of the American Black Chamber."

• 22:36Gordon Corera?

  Good name.

• 22:37David McCloskey?

  Which is a great name, by the way. It feels like it was a real miss to not have the American Signals Intelligence Agency called the Black Chamber, because that would be a great recruitment tool. So Friedman basically explains that this room contains the working files, the archives of what had been America's really premier and only Signals Intelligence Service up to that point. Now, the Black Chamber had been the creation, not of Friedman, but of a guy named Herbert O. Yardley. Yardley is a kind of hysterical character in and of himself. Very colorful guy. He's bald, he's very short, he's very hard drinking, he's a skirt chaser,

• 23:22David McCloskey?

  he's a major poker player, loves playing poker. And in fact, we're going to talk in a minute about some of the other books that he's written. The one that's, the only one that's still in print is called The Education of a Poker Player.

• 23:35Gordon Corera?

  Oh, really?

• 23:35David McCloskey?

  You can still get it today. That's right. So Yardley had started out as a code clerk for the State Department just before the First World War. After the First World War, he convinced his superiors at states and at the War Department to fund an organization that was operating under a commercial front called The Code Compiling Company in New York. And what they did was they spied on diplomatic traffic that's going in and out of Washington of around 300 countries. Do you know what one of those countries was?

• 24:11Gordon Corera?

  Can I guess it might have been the United Kingdom?

• 24:13David McCloskey?

  It was the United Kingdom, right? Shock.

• 24:16Gordon Corera?

  Horror.

• 24:17David McCloskey?

  Horror. The Americans, the Americans spies spying on people. It never, we're always surprised.

• 24:25Gordon Corera?

  We might be spying on you at the same time. So I think it wasn't one-way traffic.

• 24:30David McCloskey?

  It's maybe a moment to set up a bit of the US-UK intelligence relationship as it existed in the 1930s in the run-up to Bletchley. I think it's one of the things that makes Bletchley so interesting is that, I mean, we all, you know, we're recording this in 2026. The US-UK intelligence partnership, it has its ups and downs, but it's largely strong. It's almost impossible to imagine a world where it wasn't the case. But in the 1930s, none of the existing architecture for this relationship and most of the organizations that now participate in it didn't exist. And in fact, I mean, the US at that time had no real intelligence community.

• 25:13David McCloskey?

  I mean, there were bits and pieces of Signals Intelligence and Human Intelligence, mostly in the military services, in the Army and Navy, very unlike in the UK where you had a much more mature intelligence community. There's really no established trust as a result between the two intelligence communities on either side of the Atlantic. And in fact, you were spying on us.

• 25:36Gordon Corera?

  We were.

• 25:36David McCloskey?

  In New York.

• 25:37Gordon Corera?

  Yeah.

• 25:38David McCloskey?

  There is, there is an MI6 essentially front operation running out of what was then called the Passport Control Office in New York. It comes to be known as British Security Coordination. There is some collaboration with Hoover's FBI in this period against Nazi networks in the States. There's also a lot of spying going on against, against the US and against the FBI. I mean, it's fascinating because it's really, I mean, it's an influence operation in many ways.

• 26:08Gordon Corera?

  That's what I was thinking is, is there's a bit where the Brits are spying on the Americans. There's a bit where they're basically trying to influence American politics and they're trying to get them into the war. And so you're running an operation, which is if, in modern terms, planting information, planting stories, feeding in stories to try and get the Americans into the war. So you're right, that's, it's a very odd intelligence relationship at that time and nothing like what we have today as you get to the start of the war. But on this, the American Signals Intelligence, the code breaking, what's also fascinating is, is they've got this legacy of the Black Chamber, but the Black Chamber itself is shut down, isn't it?

• 26:51David McCloskey?

  Yeah. By the time we get to Bletchley, this thing is an art, you know, it's a relic of the past. I mean, it's why that room is so dusty that they go into. And it's shut down essentially because the Secretary of War, Henry Stimson, says famously, "Gentlemen, don't read each other's mail." And he kind of shuts the place down.

• 27:14Gordon Corera?

  What world is he coming from?

• 27:15David McCloskey?

  Once he figures out, once he figures out what's going on, what Yardley's up to.

• 27:19Gordon Corera?

  I mean, that's a very prissy diplomat, isn't it? Who's going to go, "Well, I would never want to know what my adversaries are doing." And so he shuts down Yardley's operation, doesn't he, in 1929?

• 27:29David McCloskey?

  Meanwhile, the so-called gentlemen in the Security Coordination.

• 27:33Gordon Corera?

  British Security Coordination. The Brits are like, "Yeah, we'll keep spying."

• 27:36David McCloskey?

  Well, I found this fascinating. I mean, so Roosevelt gives a speech in, I think in 1941, where he shows a supposedly captured Nazi map showing their plans for South America and this kind of partition of South America and Central America into different puppet states. And he cites this in a speech. Do you know what it was?

• 28:00Gordon Corera?

  No.

• 28:01David McCloskey?

  It was created by MI6 and fed to the Americans to make us concerned about Nazi plans for the Western Hemisphere, right?

• 28:12Gordon Corera?

  Shocking.

• 28:13David McCloskey?

  So this, this shows you how immature the US intelligence community is at this point in time, because well, at the same time, you were very cleverly seeding false Nazi maps into our decision-making. We have a guy saying, "Gentlemen, don't read each other's mail."

• 28:28Gordon Corera?

  Yeah, we do. But I mean, Stimson shuts down the Black Chamber. And this is so interesting, isn't it? Because it gets shut down in 1929, but then I think it's the War Department go, "Actually, you know, the State Department might not want this."

• 28:43David McCloskey?

  We'll take it.

• 28:44Gordon Corera?

  We'll take it. So we're going to do it, which is where William Friedman comes in, I guess. So, so American code breaking does continue, we should say, after the Black Chamber is shut down, but by Friedman, who's going to set up a new organization through the 1930s.

• 28:58David McCloskey?

  And the focus for the US in this, in this era is really Japan and in particular, Japanese diplomatic traffic where the US will start to have some successes. Now, very interesting is a system that the US has codenamed Purple. And this is Japan's highest level kind of diplomatic ciphers.

• 29:22David McCloskey?

  And it has stumped American code breakers by the late 1930s for a very long time. And it stumped the Brits, too.

• 29:31Gordon Corera?

  Yeah.

• 29:31David McCloskey?

  Because the Brits have not cracked.

• 29:32Gordon Corera?

  They've all been trying to work against them.

• 29:33David McCloskey?

  Right?

• 29:34Gordon Corera?

  Yeah.

• 29:34David McCloskey?

  And finally, though, in the autumn of 1940, the Americans get a breakthrough. Friedman and Sinkov and these, these guys who've taken over the legacy of the Black Chamber and really focused it, in this case, on Japanese diplomatic traffic, have finally been able, essentially, to recreate the, the Purple Machine, the machine that the Japanese are using to encrypt their diplomatic traffic. Now Friedman ends up having a nervous breakdown on the tail end of this. Probably, it's a little bit unclear, but probably from just essentially overworking himself constantly. And it's a very fascinating story of how Friedman and his team back-solved for the

• 30:18David McCloskey?

  Purple Device from intercepted communications. So they didn't have one in their possession. They actually built one out of old telephone equipment and had constructed this analog version of this Purple Machine. And that, I think, it's a very important piece of the Bletchley context because by the time we get to late 1940, early 1941, the Americans actually have something to offer.

• 30:43Gordon Corera?

  Yeah, they've got something to bring to the table. And it is this, the fact that they've solved the Purple Machine. They've got a, their own working version of it. It is interesting, as you said, that Friedman, who's a curious character, does have a breakdown and it is thought to be related to the stress of trying to break Purple as the war is coming and it started in Europe and obviously not yet, you know, the US hasn't yet been attacked by Japan. That's going to come later in 1941. And it would have been Friedman, I think, coming to the UK in February 1941 if he hadn't had this breakdown and needed to be hospitalized for it. And you get this sense of just the intensity of the work that's been going on within the

• 31:27Gordon Corera?

  American code breaking community at that point. It's interesting as well because they've also had issues about secrecy, haven't they? Because they've got worries about having their truths exposed because right at the start, Yardley, to go back to him, had gone public about, you know, the, the Black Chamber and he'd written a book about it. And so they had this kind of huge exposure of their codes and their information. And so they're also worried about secrecy as a result. And they've also got these fears. So you can see on all these sides, there is this question, well, we've had this breakthrough, a bit like the Brits have had with Enigma, the Americans have had with the Japanese, but do we dare share that with the public?

• 32:07David McCloskey?

  And neither know that the other side has had, has had that breakthrough. It is fascinating. I mean, and it really does lend some credence to, I think, maybe British skepticism about how trustworthy the Americans.

• 32:20Gordon Corera?

  Yeah.

• 32:21David McCloskey?

  Might be because I think at one point in the 30s, Yardley went to work for Chiang Kai Shek on code breaking. Like, he essentially leaves, like, a lot of, a lot of American sigint community at that time thinks that Yardley is a traitor.

• 32:35Gordon Corera?

  Yeah.

• 32:35David McCloskey?

  He's also done, I think, a very damnable thing because he left the intelligence community and he started writing spy thrillers.

• 32:43David McCloskey?

  Right?

• 32:45Gordon Corera?

  The Blonde Countess was one. I was reading about the Blonde Countess, actually. I went down a slight diversion of reading about, she's someone, I think, who seduces Americans to try and steal their codes.

• 32:56David McCloskey?

  She seduces a balding poker-playing, short, American code breaker. Apparently, the, so the, I was not aware.

• 33:05Gordon Corera?

  Yeah.

• 33:05David McCloskey?

  Of these spy thrillers before we started looking at the series.

• 33:08Gordon Corera?

  They weren't a big influence on you.

• 33:09David McCloskey?

  No, they were not. They have been widely panned. I mean, they're, they're not, basically what, basically he wrote them because he tried to write a sequel to The Black Chamber. And there was a gag order put on him. The galleys, the advanced copies of his, of his second book were seized. So he couldn't, he couldn't make money off of it. And so he started writing spy thrillers as a workaround to get his story out there.

• 33:37Gordon Corera?

  I think the importance of Yardley is the fact that, you know, he exposes the fact this Black Chamber existed. The Japanese actually in the 30s improved their codes because he's revealed they've broken them. I mean, it's a bit like Snowden in its time, you know, Yardley's impact, you know, it's, it's revealing the, the truth or the, you know, the reality that code breakers are stealing communications and breaking the communications. And it goes back to that idea of the sensitivity and the importance of secrecy. And also, I think it does make the Brits a little bit fearful because the Americans have just, you know.

• 34:11David McCloskey?

  Is there another Yardley?

• 34:12Gordon Corera?

  Is there another Yardley?

• 34:13David McCloskey?

  That might be coming over here.

• 34:14Gordon Corera?

  Are the Americans leaky? It goes back to that question about what can you trust them with about your code breaking successes?

• 34:22David McCloskey?

  The American team that comes over is interesting, isn't it? Because it's, it's a reflection in many ways of the fragmentation inside America's signals intelligence community. Because Sinkov and Leo Rosen are both in the army. They're in the Signals Intelligence Service of the army.

• 34:38Gordon Corera?

  Friedman's outfit.

• 34:39David McCloskey?

  Friedman's outfit. But with them are two guys from the Navy, Robert Weeks and Prescott Courier. And in many ways, these, even though they're working for the same government, these two branches of, of the Armed Forces have kind of been doing their own thing on code breaking. So there's not a, there's not a unity of purpose on the American side either as they come over to Bletchley.

• 35:02Gordon Corera?

  No, they kind of compete on the American side. Quite a lot of, and this may be familiar to you, fractious competition within the American intelligence community.

• 35:11David McCloskey?

  All 17 of our agencies work seamlessly together.

• 35:15Gordon Corera?

  Yeah. But I think in those days, the, the Navy and the Army code breakers did not get on. They also have, it's interesting, different views of the Brits. The US Navy, much less keen to cooperate with the Brits. They see actually, there's competition between the US Navy and the Royal Navy and they, so, so they, they're worried that any cooperation will actually help the Brits break American codes. Because it goes back to that idea that actually they've all been spying on each other.

• 35:42David McCloskey?

  Well, we obviously have the benefit of coming to this story with hindsight, right? I mean, at the time, there's, it is deeply uncertain if the US is even going to get into the war.

• 35:53Gordon Corera?

  Yeah.

• 35:54David McCloskey?

  Much less what kind of partnership might exist between the US and the UK on the other side. So, you know, looking back on it, it can be kind of hard to understand, well, why is there so much skepticism on both sides of the Atlantic about sharing? But in that political context, I mean, in a context where in the US, there's still, you know, very powerful isolationist political tendencies, right? There's actually a residual kind of concern about British intelligence, going back even to the First World War, where, you know, you, you actually were intercepting some of German and Mexican communications and leaking them.

• 36:32Gordon Corera?

  To get the Americans into the war.

• 36:33David McCloskey?

  To get us involved in the First World War, which many Americans were still frustrated about in the 1930s. So the cryptology, the cryptanalysis is the most sensitive stuff that's going on, on either side of the Atlantic. So it is very interesting, like, why does the Bletchley visit even come about? Because neither side actually knows in advance what the other side has broken. But it is happening in this bigger context of a lot of technical and scientific sharing that's beginning to open up, I think, as both countries see a shared sense of purpose in needing to defeat or diminish Nazi Germany.

• 37:15Gordon Corera?

  Yeah, and I think you're right. In a way, it's surprising it does happen, but there's a bit where the code breakers themselves are curious about what the other side is doing.

• 37:25David McCloskey?

  What the other side is broken.

• 37:26Gordon Corera?

  And they think, maybe we can learn something. You know, it's a bit like talking to the poles. You go, oh, hang on a sec, there's a different way of doing this. But then the other bit is, I think, they have the, the political direction from the very top, from, you know, eventually it'll be Churchill and Roosevelt, to try and work together. And I think that is important because you've got both those things coming together. And November 1940, in the context of some of these scientific and technical exchanges, you've got the chief of MI6 telling Churchill that there's a desire to talk to them about what they've done against Japan and to learn what the Americans have done against Japan.

• 38:06Gordon Corera?

  But acknowledging it would be awkward then to not reveal what Bletchley was doing on German codes. And he says, you know, it would be obvious, we have something to hide. And, and Churchill agrees and he says, maybe we should show a little leg, which is one of those, you know, which is, you know, we'll just, just show them a little bit. And I think that is the context as you hit November 1940, ahead of this February 1941 visit, is the idea, well, let's just, let's just open up a little bit, but not too much. Let's see what we can get from them. But there is one British official, when Churchill says this, adds a telling note to, to the memo about this discussion, they says, what will they think if they find we've been reading their stuff? You know, so that's the, that's the.

• 38:51David McCloskey?

  So maybe you don't tell them.

• 38:51Gordon Corera?

  Yeah. You know? You know, they, they might work out that if we've broken these codes, we've broken their codes. So they have been spying on each other and that's absolutely clear right through the 1930s.

• 39:01David McCloskey?

  The four Americans, now Friedman, as we said, stays back because he's had some kind of nervous, nervous breakdown. They leave Annapolis, Maryland on a frigid cold day in January of 1941. Their journey itself is kind of an interesting part of the story as well.

• 39:21Gordon Corera?

  Yeah, dangerous.

• 39:21David McCloskey?

  Yeah. So they're going to travel on the British battleship King George V. Now, all of these guys were essentially Army and Navy Reserve, who then have to be formally called up in order to be able to travel on a, you know, foreign flagged battleship over the duration of what will become a two-week voyage, a very unpleasant, I think, two-week voyage across the Atlantic. They pretend to be Canadian.

• 39:45Gordon Corera?

  Lucky them.

• 39:46David McCloskey?

  For the sake of protecting their real identities.

• 39:48Gordon Corera?

  It's a promotion, isn't it?

• 39:49David McCloskey?

  Right.

• 39:50Gordon Corera?

  Sorry.

• 39:51David McCloskey?

  I'll hold my tongue because we're trying to get some Canadian intelligence guests to come on for our Declassified Club members, so I will, I will say nothing. One of them, I forget who it is, said that they're Canadian, the ruse of them being Canadian fooled no one on the voyage. None of the Brits were confused. The ship heads for the Orkneys at Scapa Flow.

• 40:14Gordon Corera?

  Yeah, which is a sheltered harbour at the north of Scotland. And from there, the plan is for two flying boats to come and take the four Americans and the equipment that they brought down towards the south. But the problem is that they've got this equipment in big crates and they've got nearly two tonnes of equipment and it actually won't fit through the doors of the flying boats. They suddenly realise we can't do that, we're stuck. So instead, they go on the Neptune, a pretty battered old ship. I mean, barely afloat, I think, is the honest truth.

• 40:55Gordon Corera?

  And that comes up to pick them up and it comes down then the eastern coast of Scotland and then England. Problem is, this is where it gets dangerous because it gets spotted by a German reconnaissance plane on the way. Next thing, two German dive bombers appear. And Prescott Currier, one of the Americans, says, "I was trying to eat some soup, but my mouth was so dry I couldn't swallow it. I've never been so scared in my life. We heard a bomb landing on one side and one on the other side, and the ship would bounce out of the water and back down again. Then I heard something that sounded like someone dragging chains along the deck."

• 41:36David McCloskey?

  Did he have a bowl of soup that whole time in his hands? That seems, it seems like, just the whole time, he's holding on to the soup. They're bringing with them that reconstruction of the purple device. It's one of the most valuable pieces of technology that the US government has in its possession at that point in time. So.

• 41:59Gordon Corera?

  And the problem is.

• 42:00David McCloskey?

  Is it destroyed?

• 42:01Gordon Corera?

  It's on the deck.

• 42:02David McCloskey?

  It's on the deck.

• 42:03Gordon Corera?

  It's on the deck of the boat. And when Prescott Currier talks about the sound of someone dragging chains along the deck, that is actually German guns strafing the deck of the boat and firing along the boat where the purple machine is being stored. And there's something like half a dozen passes by these German dive bombers. And Currier thinks, "God, I thought all that gear is stacked up on deck unprotected, absolutely unprotected, and I was so scared, I couldn't go up and do anything about it anyway." And he thinks, "Well, that's the purple analogue gone." I mean, it's a pretty close-run thing, but fortunately, the bullets don't penetrate into the crates themselves.

• 42:47Gordon Corera?

  Interesting enough, this is thought to be one of the first times Americans come under fire in World War II because they're being shot at by Germans. Of course, America isn't yet into the, in the war, it's not till later in the year after Pearl Harbour. And here they are, because they're undercover, as Canadians, that they're getting shot at by, you know, by Germans. And so they're experiencing, and I think this is one of the important things about this visit to Bletchley, and there'll be other moments where they feel this, they're experiencing the reality of war.

• 43:16David McCloskey?

  Yeah.

• 43:17Gordon Corera?

  You know, and they're seeing what it's like for, to come over the Atlantic at risk from German U-boats and then to see the German planes strafe them, you know, as they're on the Neptune, coming down the coast. They are seeing that this is the reality of what it is to be a country at war and to be under attack. And I think that's going to have quite a powerful emotional impact on these Americans as well.

• 43:38David McCloskey?

  So then at Shirena's port, Kent, on the southeast coast, they arrive on February the 8th, probably a little bit sort of worked up from the, from the journey. They're met by a gentleman named John Tiltman and they head here. They come to Bletchley Park where they will arrive late at night and be served sherry. Now, was the sherry, why sherry? Was it rationing from the war? Because I would, I would assume, maybe this is wrong, maybe this is my American ignorance. I would assume sherry isn't maybe the first choice in that instance?

• 44:13Gordon Corera?

  Do you not drink sherry?

• 44:14David McCloskey?

  Well, I think it'd be like a whiskey or something.

• 44:16Gordon Corera?

  You know what? I think whiskey was maybe harder to come by.

• 44:18David McCloskey?

  Okay.

• 44:19Gordon Corera?

  But, but as we started this episode, you've got the head of Bletchley Park, Alistair Denison, saying to his assistant, "Get ready for these Americans, get the sherry ready." Because I think that he just knows they need a drink.

• 44:31David McCloskey?

  Yeah.

• 44:32Gordon Corera?

  I think that's what it is. I think, I think the fact it's sherry is that's the only drink that they've probably got. And he knows they're going to need a drink, he knows it's going to be a long journey, and he knows, I think, that this is going to be a very important meeting. And I think you can, if you go back and imagine what it would have been like at this moment, a lot is riding on this because you're trying to kind of build cooperation, but also you're fearful, aren't you? Because you're fearful about giving away too many secrets. How far do you go? What do you tell the Americans? Do you trust them with the secret of what's happening inside the huts, of what Turing has managed to achieve when it comes to breaking Enigma?

• 45:13David McCloskey?

  Well, especially from, from the British perspective, the cracking of Enigma could be the difference between life and death, being able to survive 1942 and 1943. And then also, frankly, you know, and we'll talk more about this in the next episode, the impact, but the number of people, soldiers, civilians otherwise, who could be potentially saved if you crack this code is very significant. And so as the Americans arrive, I mean, you know, it seems, again, in retrospect, like inevitable that it would be shared, but if you, if you share it with the Americans and then you have another Yardley situation and it gets leaked, it's, it's probably the most

• 45:55David McCloskey?

  important piece of technology that your country has, the most important capability. So when the Americans show up at Bletchley, the plan at that point is, as Churchill said, to show them a little leg.

• 46:08Gordon Corera?

  But not.

• 46:09David McCloskey?

  But not to share Enigma.

• 46:10Gordon Corera?

  Yes, and that's the crucial fact, is that night in February, when they come up the drive, when the sherry is waiting, the plan is not to tell them about Enigma and the breakthrough that's been made by Turing and by others here at Bletchley Park into breaking the code there. And so that is the key question, which is, what will happen during this visit? And can you trust the Americans?

• 46:38David McCloskey?

  That sounds like a proper cliffhanger there, Gordon. Let's end it there and when we come back, next time, we will see if you actually can trust the Americans.

• 46:46Gordon Corera?

  A reminder, though, that if you want to hear that episode straight away, you can if you're a member of the Declassified Club, and you'll get access as well to the bonus episodes, including a Q and A here at Bletchley Park. And we've got some other great material coming up and some big series and some very exclusive interviews. So do join up at therestisclassified.com. But otherwise, we'll see you next time.

• 47:08David McCloskey?

  We'll see you next time.

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