“Alan Turing: Codebreaker, Visionary, Enigma” – with Andrew Hodges

Andrew Hammond: Welcome to "Spycast," the official podcast of the International Spy Museum. I'm your host, Dr. Andrew Hammond, the museum's historian and curator. Each week we explore some aspect of the present, past, or future of intelligence and espionage. If you enjoy the show, can we please ask that you leave us a five-star review. It really helps other listeners find us, and will take less than a minute of your item. Coming up next on "Spycast."

Andrew Hodges: Always hanging by -- hanging by a thread is one of the expressions that they used. They knew that the whole thing could collapse at any moment.

Andrew Hammond: Right, right. [ Music ] This week is the 70th anniversary of Alan Turing's untimely death at the age of 41. Turing was a British mathematician, best known for his contributions to theoretical computer science and codebreaking, work that was critical in cracking the German Enigma code during World War Two. To commemorate his life and achievements, we spoke with Dr. Andrew Hodges, an emeritus professor of mathematics at the University of Oxford. In 1983, Andrew published one of the first books to explore Turing's story and his work on Enigma, a book that would later become the inspiration for the hit 2014 film featuring Benedict Cumberbatch, The Imitation Game. In this episode, Andrew and I discuss Turing's foundations for artificial intelligence, anti-war codebreaking or cryptanalysis; Bletchley Park, Hut 8, and British naval intelligence, and the mechanics of The Bomb machine. The original podcast on intelligence since 2006, we are "Spycast." Now sit back, relax, and enjoy the show. [ Music ] So thanks ever so much for speaking to me, Andrew. As my colleague Erin pointed out, it's one AH speaking to another AH today. So I really appreciate you coming on the show to talk to me [laughs].

Andrew Hodges: Well, thank you for inviting me, AH. It's a pleasure to be on your program.

Andrew Hammond: So I think it would be interesting just to start off, tell us how you first came to be interested in Alan Turing.

Andrew Hodges: Well, that goes back a very long way. I think it was in 1969, when I was 19 and an undergraduate student at Cambridge University, and I was reading around about things in the background of mathematics and computers, and I came across his name, just the name, really. But then shortly after that, in the early '70s, I came across his name in quite a different way as a gay man who'd suffered very considerably in the prosecution after the war. And I was interested for a start. But then what really got me going was in 1977, I learned that really he'd been the most important person in the code-breaking effort during the Second World War, which at that stage was just emerging into public knowledge. I mean, not very many people knew. It had all been kept very secret for 30 years. But in a funny way, I was one of the few people who caught onto all these different strands. I knew about serious mathematics and mathematics and science. That was my business. At that time, I had a PhD in maths. And I knew about the gay history part of it, too. I had a real feeling for that, and how the times -- what they were like in the 1950s. And also then there was this amazing historical story which was just breaking out. And it turned out he had not only been in it, but was really the most important scientific figure in the British and in fact in the Anglo-American effort between 1939 and '45. And I thought that was an amazing story, really. And I just wanted to do something about it.

Andrew Hammond: And tell us the Turing that you found when you started conducting the research for your books. So for our listeners, your book comes out in 1983, or the first edition comes out in 1983. And this is a seminal book on Turing. But now, all these years later, where he's on the 50 pound note, and there's an Alan Turing institute, and Gordon Brown issued an official apology. And there's the, you know, people that were convicted for homosexual offenses in that era have been pardoned and so forth. But I'm assuming it was very different when you were doing the research for the book leading up to 1983. What was Turing's status among the general public, or British history when you took up the baton, so to speak?

Andrew Hodges: I could sketch that. I mean, he certainly wasn't famous in the way that you've been explaining. In mathematics, he was well -- fairly well known as the concept of the Turing machine, which is really this organization of an algorithm. Algorithms now get a very bad press, but they didn't -- hasn't always been the case, and he was the person you really defined what an algorithm is. That was his thing before the war. So that known in mathematics. There's a famous prize in computing science, for instance, the A.M. Turing Prize. And that had been established in 1960s. He was not an unknown figure in that way. But not to the general public, no, he was not known at all. There's a certain amount of -- scientific public would have known a bit more about his interest in artificial intelligence, because he wrote a very lively, very readable, a very -- well, almost funny, really paper about artificial intelligence in 1950, which has always I think been the most -- well, it's been one of the most accessed and quoted papers in the whole field ever since. And that was known about. What wasn't known at all, and still isn't really known now is that in between those things, between the codebreaking and the artificial intelligence ideas, he invented the computer. I mean, that's what he did in 1945. It came out of the codebreaking work, putting the algorithms and the technology and his theoretical ideas together, he had the most enhanced computer plan in the world in 1946. But he was picked by John von Neumann who is now famous really as the creator of the modern digital computer. They were very much on a level. They were on a par, really. And it's a big argument about how much von Neumann got from Turing and so on. It's a very complicated story. But that was the essential bit of it, really. That was the thing which made him the founder of computer science, the beginning of the whole digital world, really. Everything that you do with the digital, everything that we're doing now through these computers flows from his perceptions. And that in turn came from his practical experience during the Second World War on breaking the enemy codes.

Andrew Hammond: So we have a variety of different contributions, then. We have contributions in mathematics, artificial intelligence, computing, cryptography, just really across a whole variety of different fields?

Andrew Hodges: Absolutely. The breadth of his interests is really quite extraordinary. I mean, he would have called himself a mathematician. That was his, you know, professio, but he went way outside that into philosophy and the theory of mind and how a machine can or cannot emulate what a mind does. But also much more than other mathematicians, into engineering. He got really seriously interested in electronics, and actually designed the electronic components and the circuitry for the computer that he designed. These are very unusual things to do, and that breadth is really what makes his story very interesting. Of course, he wasn't -- didn't make it very easy for me, because I was supposed to find out about all these different things. But since -- coming back to your question about what it was like starting on all this, I think the thing I go to is really the people. The people he knew. The friends he had, the colleagues he had, the goodwill that he left behind, which I was very grateful to get, you know, flowing onto me. And the whole sense of story that flowed out of that and what people could tell me with putting together with all the bits and pieces of papers and memos and letters and so on. It was a fascinating business to get into. And for me, just asking about that, it was like living a previous life. It was like getting to know someone who was, you know, 30 years older than me and had his life cut short when really getting into the -- him as much as I could. Of course, no one really can, but I did my best.

Andrew Hammond: And as an emeritus professor at Oxford, you maybe don't have this feeling, but whenever I do a podcast on people like Turing, I always feel like a chronic underachiever [laughs]. Is that something that you encountered when you were doing the research for your biography?

Andrew Hodges: Well, it was exciting as well. And then that was the thing great man has a quality -- there's a real story to it. There's real -- it's more than most people's, I think. But it went from something that was just thinking and theory, but he had this great wish to do something with his life, do something with his hands. It was really sort of down-to-earth, concrete thing. And that -- first of all, that came about through the codebreaking work, which we'll probably come onto later, and in a bigger way really, through the idea of the computer, everything you can do with the computer. So that makes a story of growth and then a prophecy of what's going to come in the future. I mean, he's more complicated than that. He did lots of other things as well. Other things in pure mathematics. He worked in biology. There was a wonderful sense that I enjoyed very much of a storytelling narrative of growth and discovery.

Andrew Hammond: And I just want to touch on this briefly before we get into more depth about Enigma and his contribution, Bletchley Park and so forth, but whenever you do research on Turing, you inevitably come across two papers, and I believe that one of them you probably already referred to, which is the "Can Machines Think?" And then the other one, which is at the opposite end of the spectrum in terms of approachability is the one on computable numbers. So just for the layperson, what's the contribution of both of those papers, for like a layperson?

Andrew Hodges: Yes, absolutely right, certainly right those are the two pivotal things. And the pre-war one is the one -- 1936, and this one I referred to as the way that he defined an algorithm. And that's what he did in this paper, which had this peculiar name, but that was the thing he was most famous for in mathematics. They're actually related, those two papers, because they're both about a question of mind, and how a machine can emulate what a mind does. So even in the pre-war work, he was thinking about human minds. He wasn't actually thinking about physical machines so much. He was thinking about the question of what can a person do -- and it was a person doing when they're following something that you call a method, as we now call an algorithm. And he formalized this in a very clever way into this concept of a Turing machine. And what's very striking now, and very striking after the war, was that he came up with this concept of a universal machine which could do anything. Well, it could perform any process. And then of course, that's exactly what we think of a digital computer as doing. It can play any program that you give it to do. And that was completely new. So that was foreshadowed in the 1936 work, but then flowered completely in 1945 and gave an entirely new picture of what computation was all about. And now essentially it's taken over the world. I mean, everyone's -- I'm talking to a universal machine, you're using one. Everyone, you know -- there's hundreds of millions of them around. And that really all flows from his perception, which was really, really then completely new.

Andrew Hammond: The other day, it was just -- I had a little smile to myself, and I thought of how much excitement Turing would get if he came back to the future just now and saw Chat GPT or all of this -- the discussions about artificial intelligence and generative AI and so forth.

Andrew Hodges: Well, that's absolutely true. In fact, it's quite uncanny how a text message formalism that he thought of for -- or what you'd imagine doing to testing a machine as to whether you thought it could be considered as having intelligence or not. He had this text message protocol. And the point was it was a message used with jokes and subtleties and fooling and risqué observations and so on. It's just so like what people actually do, which he couldn't possibly have known. He wrote this when there were only a couple of computers working in the world. But he did see this human level to it. That's what people actually didn't like very much at the time. The more serious -- more conventionally serious people at the time said no, no. Computers are just doing calculations. He did see a long way beyond that. He imagined a world in which people would be communicating and doing everything in life, really, in terms of computing. And then posed these questions about what do you call intelligence and so on. So yes, he would have seen this very direct thing.

Andrew Hammond: And I mean, I even think about this with Recaptcha now which is as I understand it -- correct me if I'm wrong -- is a kind of Turing test to tell humans and machines apart, and this is something that people are doing like very, very often.

Andrew Hodges: Yes. That gives a little flavor of it. I mean it's nothing to the scale that he envisaged, but it does give the flavor of it. It's trying to -- as you say, it's a capture, something that's you can imagine only the human knows, maybe what a motorcycle is, or what a lamp post is, and those sort of things. And you think it'd be very difficult for a machine to do. Well, of course, actually machines can do quite a lot of those things. It's not really so clear cut. But that is the sort of thing that was in his mind, yes.

Andrew Hammond: And just very briefly before we move on to Enigma, what's a Turing machine for the average person on the street?

Andrew Hodges: Well, it's an algorithm. It's a computer program. I mean, one way of putting what he did in 1936 is that the abstract question in mathematics was, how do you define what you call a method or a procedure? And he found an answer to that, and his answer was, it's a computer program. I mean, that's a very definite answer. Some may actually write down a list of symbols and that means you can do it. But computers didn't then exist, so he had to invent the computer so as to make sense of that definition. Well, of course, that -- I'm talking in a not very literal way there, because you don't really invent something that doesn't exist. But that's the -- gives an impression that what he did was important, and how ahead of his time, and how he came up with the idea of a computer well before any machines actually existed. And now, incidentally I mean, you have a very direct sense of what a Turing machine is, because if you click on an app on your phone, you are simply moving the operation from one type of process to another type. Just in a millisecond. And it goes from doing GPS mapping to doing voice recording to doing calculations to doing scrolling through your messages, because at effect it just changes from one thing to another. And that really is the principle of the universal machine. That you can do all of those things without even doing anything to the hardware of the machine at all. It's all done as we now say on software. And that was really his idea. I think looking back in the 1930s when he did this, no one I don't think had ever come up with this concept of a universal machine. And there's loads to talk about machines. The Victorians are fascinated by machines. Lots of H.G. Wells and people like that were very interested in machines. But all thought about different machines and different tasks. And it was quite a breakthrough idea, which took a long time to catch on commercially after the war, that you would have one machine do all these different things. It could do scientific calculation, it could be doing your invoices as well, and writing letters, or whatever. But you only need one type of machine. That's very new. [ Music ]

Andrew Hammond: It's just -- it's so incredible and so fascinating how he presaged the world in which we currently live in so many ways. [ Music ] You may have heard the story of how the famous Apple logo found on the back of your tablets, laptops, and phones was inspired by Alan Turing. For anyone a bit lost, I'll fill you in. Alan Turing died at his home in June of 1954 of cyanide poisoning. He was found by a housekeeper who discovered Turing rather peacefully in his bed with an apple lying half-eaten next to him. His death is a bit of a mystery. Ruled a suicide by most, but believed to be accidental by quite a few others. Whatever the nature of his untimely death, this image of an apple with a bite taken out of it was thought to have been the inspiration behind Steve Jobs's company logo. This makes sense, as we've mentioned in this episode already, because Turing is one of the fathers of the modern computer. Unfortunately, this theory is nothing but an urban legend. The company has confirmed it has nothing to do with Turing, as clever as that would have been. While the Apple logo may not have been inspired by him, plenty of other theories, organizations, and inventions bear his name. For example, The Alan Turing Institute, UK's National Institute for Artificial Intelligence, The Alan Turing Building at the University of Manchester, and the annual Turing Award, given by the Association of Computing Machinery, among many, many others. Since 2021 meanwhile, Alan Turing has been featured on the reverse side of the 50 pound Bank of England note in the United Kingdom. [ Music ] [ Soundbite of digital beeping and typing ] I think it would be interesting now to pivot on to Bletchley Park and Enigma, so tell our listeners, how did he first get caught up in all of this? Was it through his networks at King's College, Cambridge? How did he get recruited into codebreaking?

Andrew Hodges: Right. Well, there's a very interesting story here. Of course, there's a social, academic side to it, that he came from an elite background, was at a top Cambridge college, and was surrounded by people who were all in with the Maynard Keynes in particular, the economist. Very close to top people in government. Knew all about the First World War codebreaking business. And so it was just an open door to push at there. That's on the social level. But on the international level, the very interesting thing is that he started thinking about codes and ciphers in 1936. It was a spinoff from the work that I've just been describing about what an algorithm is. He thought, what would an algorithm be if it was doing a code, or breaking a code, or whatever? I mean, he went into that area then, right? Straight away in 1936. And not only that, but he, you know, devised a particular new type of cipher system, which he built out of electromagnetic parts when he was away at Princeton in 1937. So a real hands-on interest in this subject. And that's together with the social background, and of course, the political background where everyone was seeing the war with Germany was coming. That is what compelled him to make an approach to the predecessor of the GCHQ is now, actually a powerful organization, the government organization that dealt with codebreaking. And he did that in the summer of 1938, well before the war started. In fact, he was really almost invited in. They were looking for people with a mathematical, scientific basis who could do something for them. They knew that the problem of the Enigma was that it was much more scientifically based than the First World War coding systems had been. They needed someone who could cope with that material. They were absolutely looking to recruit such people. And really Alan Turing was absolutely perfect for it. He was exactly what they wanted. He had a very good theoretical understanding of what coding was all about. What information was all about. What symbols are all about. And Enigma making symbols at a very high level of theoretical understanding. But he had this real practical sense as well, and together with an engineering sense of what you would be able to do with machinery that existed in those days, which essentially automatic telephone exchange-type equipment. So it was a marvelous thing where it was just the right person at the right time in the right place. And the other ingredient that really got things going was the mathematical work done in Poland. The Poles and their crypto organization were miles ahead of anyone else, and had made mathematical understanding of the Enigma coding system, which I'll say a little bit more later. And they transferred that to the British and French, just before the war started in July 1939, and that was a tremendous stimulus. And Turing took off from those ideas, and that's -- everything went off like -- well, it just exploded from that point on, very early after war was declared in September 1939.

Andrew Hammond: And I'm just trying to get a sense of the sweep from World War One through to World War Two, Andrew. So I'm thinking of World War One and Room 40, sort of the British Navy, the Admiralty Unit that's trying to crack German codes. We've got these archeologists, classicists, and so forth. Dilly Knox and Alastair Denniston. These types of people were around in the First World War, and some of them carry over into the Second World War, but as I understand it, and tell me if I'm wrong, in the First World War, it's more -- they're looking at languages. People are looking at archeology, people are looking at papyri and so froth. Whereas when you get to the Second World War, it's much more mathematical and engineering and so forth. Is that fair, and is that because of the shift in technology?

Andrew Hodges: Well, you're absolutely right there, and the more literary people that were very good, I'll say very competent on the First World War type of codes based on code books. And Dilly Knox, who you've mentioned, was clearly a very ingenious character all together. And actually did make headway on the simplest form of the Enigma, which was in use by Germany and indeed by other countries in Europe in the 1920s and '30s. But the key word is, it's still a machine. And the machine, it was more mathematical. And it did need a mathematical approach to it. And none of the people who came from that First Word War generation had quite that skill. They were actively looking for people to beef up their abilities in that area. And Turing wasn't the only one, but he was the first one, really. And he fitted that bill perfectly. I would say, I mean, it's usually thought that the -- it's another important thing is that thing -- you know, about the Enigma, it's often thought about -- I think you've indicated that, so it wasn't the great sort of mystery, the basic Enigma was a commercial machine. And it had been invented in 1920, and lots of people had it. The point about the German military use of it was that it was very considerably enhanced with an extra complication. But the basic form of the machine was not a mystery at all.

Andrew Hammond: But that experience of -- the British experience of World War One cryptography, did that in any way spill over into -- to affect mathematics in the interwar period, or the types of things that people were looking at, or even the invention of the Enigma machine in the '20s and '30s, did in any way this spill over? Or were the mathematicians really sort of reacting during the Second World War to the developments that had taken place?

Andrew Hodges: Yes. Well, there are also elements there, the machine scientists were not really in development answered those First World War methods. And there were various different types of [inaudible 00:28:04] machines, which went back a long ways in the 19th century. And that was really quite a different thing from the book codes that were used in the First World War. There was a lot of crossover in technique and understanding of what was going on. I mean, Dillwyn Knox certainly took to Turing and they got on very well, only parted in the war. And Knox's whole familiarity with the whole business of cryptography I'm sure was actually very important in getting into the whole thing. And just because you had machine methods, that didn't mean that you lost sight of the psychological aspects of what coding was all about. I mean, they would use ideas based on what the German [inaudible 00:28:53] agents were doing on their machines when they set them up. They did a lot of very fine guessing to get going on these things. So the human element, the heuristic element, the guesswork part of it, the playing around with -- [inaudible 00:29:10] guessing probable words in a message was very, very important. And you needed some understanding of the material, who was sending it, who was getting it, how long it was when it was coming and so forth led to an understanding of what the message would likely be about, because that was essential to the mechanical codebreaking method. So there's not just an either/or of machines do this and throw away the human intuition and perception and analysis. Not at all. They had to work together. Turing was certainly on the mathematical side, and in fact, what he did apart from the basic algorithm for the Enigma was really to develop a mathematical theory of statistics, which was then used throughout the war. But he would have known very well that he needed a lot of good guessing, a lot of human knowledge, a lot of military knowledge, a lot of common sense to get the whole thing going. And I'm sure he had a lot of respect for that as well.

Andrew Hammond: You can see how all these components come together, the practical experience, the more humanistic interpretive skill set, the mathematical skill set, you can see how they all work together during this period. And I find it really interesting and also quite difficult, because on the one hand, you know, when you're telling the story of Bletchley Park, for example, you want to highlight that this is in some ways an industrial operation with thousands of people and various components, but then on the other hand, you know, there's the role that people like Turing have played and by all -- any yards that he's generally considered a genius. So on the one hand, it's this single genius cracked Enigma. We know that's not the case, but on the other hand, it wasn't just the industrialized method that -- it did take the contribution of people like Turing to actually make the breakthrough. So I'm just wondering, how would you best describe that kind of interplay to our listeners?

Andrew Hodges: Well, there's an enormous growth, you see. I mean, it started off a small department, about 30 or so people. And very informal working, close working together, and not a lot of machines or anything. And then that grows throughout the war, especially with the growth of war operations and the growth of Anglo-American alliance as well, and the spread into the Japanese War and everything else, into this enormous operation, in which thousands of people were involved. Essentially taking over pretty well that the whole British higher education set to -- our university at work on the -- on German and Japanese codes. But that is not how it starts off in this funny country house atmosphere. Very 1930s, a bit like a Agatha Christie or P.G. Wodehouse setting something like that. Quite upper class, and lots of, you know, of games and an atmosphere of being very exciting, but like a party game. Difficult to express, I think, but it managed to keep a human level to it all the way through. But there is enormous growth. But Turing was in it from the very start. I mean, before its start, 1938. And it was his seminal idea which gave rise to these particular machines called The Bombs after the Poles that had the first basic machine method. And those were the essential workhorses of the Enigma breaking. And you -- that was Turing. Well, I say that was Turing's, but actually he had a lot of help from the Poles and also from a colleague called Welshman who put in an important idea which he'd missed. But they got it together very quickly. That's something which I think is not always understood. Turing got his ideas together, and the machines being built already in November 1939. It was first tested in March 1940. That was long before the war really got started, before Churchill took over. It was a very, very effective start on the whole business. And that's important, because I think if they hadn't gotten that start, they would have found it far more difficult to catch up later on. The German systems using Enigma made much more complicated, and it was only because they got in at the beginning that they were able to get some -- make a -- increase their attack and keep up with it. So the timing here's terribly important. And it was a miracle really that Turing had those ideas and could put them together with actual implementation in working-part machinery in a way that he did, in the early part of 1940.

Andrew Hammond: And give us a brief anatomy of Bletchley Park. So we hear about Turing at Hut 8. What was Hut 8? What did it do? How many people were there, and what were some of the other significant parts of the enterprise?

Andrew Hodges: Thinking about Hut 8, which you've mentioned, it handled the naval signals. And that's what Turing took over in 1940. It was seen as the most difficult, and it was the most -- the one that had the most security around it, most complicated system for using Enigma, that is. But he took it on as a challenge. And it was not at all straightforward, doing it. It wasn't just broken like that. There were lots and lots of difficulties with it. But is what they did they got naval messages, which meant both surface ships, Mediterranean and elsewhere, and also the U-boats. And of course, those parts of the war, those naval aspects, are the most dependent on information. You -- they absolutely -- a naval war is all about information. You've got to know where the ships are; where the U-boats are to have an attack or defense. All about information. And so getting actual first-hand messages in real time, it was absolutely the most vital thing in that period of the -- throughout the Second World War. But the other huts, Hut 6 dealt with Army and Air Force. Hut 4 was for interpreting the messages. That wasn't so much Turing's business. But they all had to work together because you had to know a lot of the content of the messages in order to -- to break them. The two things, they're symbiotic here. And then as I've said, the number of people working, and the number of machines working increased enormously. There are 211 of these codebreaking Bombs in the Bletchley area by the end of the war, and more built in the United States as well. We just started with one, you see, and it just grew and grew. All of them needed operatives who looked after them and went through the procedures, load them with the instructions and so on. And they did an enormous business.

Andrew Hammond: And just out of interest, why was Turing sent to Hut 8? Was it because it was the most difficult one to break? Was it intentional or was it happenstance?

Andrew Hodges: He wanted it. I mean, he took it on because it was seen as the most difficult. And he did indeed come up with a very ingenious -- well, several very ingenious ideas. But they were very stuck to begin with. Well, there were several reasons for this. The first reason is that the Enigma used for the naval messages typically had more rotors than the others. It had eight rotors. You took three out of a choice of eight, rather than three out of a choice of five, which made far more possibilities to work through. So that was one. And they didn't have the rotors. They had to capture those off Norway in 1940. And then the other thing is it's all very well in using the machines as they did to break a single message. If you can guess what's in the message, then these machines were such that they could by working through all the possibilities work out what essentially the Enigma machine was for that message in a matter of hours. That's already a great breakthrough, but that's not enough. You want to break all the messages. I mean you can't do that for every single message. Even ones that have a system, you want to know the system by which the keys to the other messages are all hidden inside the transmitted messages. Now that system -- that the thing you are actually breaking. It's insane to think that the Enigma machine itself was a great secret. It wasn't. It was bound to be captured in warfare, and it was. What's important is what we now think of is the software. It's how you use that machine. It's the instructions for using the machine, how it's set up, how the -- like the password essentially is encoded within the message itself. That's what you've got to figure out, and that's what they had to work out. And there was quite a complicated way that this was done for the naval messages, which they didn't get into until they managed to capture some papers in 1941, early 1941. And even that shouldn't have been the end of the matter -- or it wasn't the end of the matter. But they managed to keep going until in 1942, the German, the Navy introduced a four-rotor Enigma which was that much more complicated again. And the numbers were such that that just really should have pushed it over the edge of what was practical to break. As it was, they had some very ingenious ways of getting around that, and in collaboration with the United States, building a whole lot more of these machines, they were able to keep on top of the business the rest of the war. But I want to emphasize it wasn't just one moment of breaking Enigma. Turing's basic algorithm which he saw and put together other people's ideas, and the very meaning of the war was an essential part of the process, and he's famous for the algorithm. But that was just the beginning. You had to make this thing actually work in practice. They had an enormous amount of -- every trick in the book really, to guess the messages, and then get one message coming in and then get to all the other messages in the key in the same system. And that was -- you know, that was essentially -- well, it's like a major scientific program, you see. That's how they attacked it. But with a difference from a scientific program is that they didn't have a long run. It's not -- in the long run, they might have said yes, they'd have done it. But they didn't have a long run. It was a matter of months, days, weeks. And it -- things were changing all the time. And the systems could be changed any moment, as they were in 1942. So that always hanging by -- hanging by a thread is one of the expressions that they used. They knew that the whole thing could collapse at any moment. Very, very exciting story. [ Music ]

Andrew Hammond: As we've mentioned, Turing worked in Hut 8, the branch of Bletchley Park that worked to break German naval codes. In this interlude, we want to give you a brief idea of what was at stake for the team in Hut 8. This was no mere intellectual exercise. The fate of their country was on the line. Naval intelligence was absolutely critical for the conduct of the Second World War. Winston Churchill believed that the Germans had the best chance to defeat the Allies on sea, stating after the war, The only thing that really frightened me during the war was the U-boat peril. I was even more anxious about this battle than I had been about the glorious air fight called the Battle of Britain. The so-called Battle of the Atlantic waged on for the entirety of the war, from 1939 to 1945. The ability to read the enemy's core communications meant the possibility of knowing the location of German U-boats and better protecting Allied merchant ships carrying priceless resources and supplies to the British and to the Soviets. Thus, the importance of Turing and the entire team at Hut 8's work cannot be understated. The British relied on receiving supplies from North America, period. Yes, many factors contributed to the Allies' eventual success and the gradual weakening of Nazi forces both on land and air, but winning the Battle of the Atlantic was perhaps one of the most vital elements of eventual victory. [ Music ] [ Soundbite of digital beeping and typing ] And here at The Spy Museum, we have a three-rotor and a four-rotor Enigma, but could you just tell our listeners a little bit more about that, and the story that we would normally hear as the German Navy especially just felt like something was up, so they added an extra rotor and the Allies were locked back out of Enigma for a period of time? Could you just tell our listeners a little bit more about that story?

Andrew Hodges: Well, yes. It was introduced in February the 1st, 1942, the four-rotor machine. Only on the Atlantic U-boats, I think. And it's clear obviously they thought something was going wrong. I mean, clearly, they wouldn't have done this if they thought Enigma was perfectly alright as it was. But as I've said, Enigma was not the most advanced or perfect or well-thought out system you could possibly have. And the British had actually done better enhancement of it. And if the German military and Navy had done that right from the beginning, I don't think they would ever have had their codes broken. It's really -- it's quite a basic thing about numbers here. And even -- basically you've got a million or so settings of the three-rotor machine to go through, and that you can do that in hours. These Bomb machines, they were a bit like solving a Sudoku problem without some logic, contractions, and persistency in finding a unique solution. That sort of thing, they would do many times and set them by going on for hours, you would get through a million of them. That's the basic numbers. But you may -- if the numbers had been 20 times bigger, every hour would have been turned into a day. And this was a miracle really, that it was just possible. The pressure was always on to speed up the machines, so electronics came into the picture in 1940. Certainly by 1942, trying to make the thing faster, but Enigma wasn't really very suitable for that. Electronics are much more suitable for the binary type things, a different type of cipher system which came in later. So there was always this pressure, always this difficulty, and always this sense of only just working. Had Germany made a more wholesale change all at once without any overlap of message or anything at all, they probably would have succeeded. I think they did do something like that right at the very end of the war, and it was too late. So it's not a simple story that's all about breaking the code. It's breaking and re-breaking and then breaking off and then breaking back. And the game that's being played between the two sides, but neither of them know quite what the other's doing.

Andrew Hammond: This book about this previously, The Bomb, can you just tell our listeners a little bit more about that? So I'm just trying to get -- we know that he's in Hut 8, what was Turing's signature contribution? As I understand it from your book, The Bomb was part of that. Can you tell our listeners what his contribution was, and what the Bomb was?

Andrew Hodges: Yes. Well, The Bomb, it was a basic workhouse. So if you had a cipher message, and if you could guess about 23 letters of it, what they actually were as plain text, and you could put the two against each other, you could set that up in this machine, and it would work through all the possibilities for the settings of the machine, and with any luck, would come up with the answer. And it would guess it absolutely correctly. And by a miracle, they could just do that. So that needed a very clever algorithm for eliminating all the settings that couldn't possibly be true, and that was Turing's contribution. I think that together with the knowledge that this could be implemented in the kind of moving-part technology that we used for telephone exchanges at that time. This is pre-electronic era. So he did that, and in taking in other people's ideas as well. And very quickly, as I've said. That was put in operation within really quite amazing speed by early 1940, long before the war got really going. So that was what he did. But as I said, that was just the beginning, see? The -- just as you can break one message, it doesn't have much use, really. You want them all. You can get any sense of what's going on, and that's where it needs a much more systemic attack on the -- using the nature of the -- consistent. How the key to each message is encoded within the message itself. And this is a major problem in any kind of cryptography now. You have -- it's always a problem with secret keys of how the sender and the receiver are going to agree on the key to each message. Do you arrange it all in advance? Do you hide it in the message itself or what? You see? And every way has got some difficulty. And the only way out of it really is what's came in the 1970s, is public key cryptography which relies on a completely different way of looking at it. That's not relevant to the Second World War period. So that was -- yes, that was Turing's first major contribution, was the machine, as I've said, they built hundreds of them eventually to deal with all these different types of Enigma, and that just grew and grew until the end of the war. But what he had to do was much more than that.

Andrew Hammond: Just as we get towards the end here, what was it like for you? You know, you're doing this pathbreaking biography of Turing, you know, many years ago now, 1983. And then -- and more recent decades and years, he started to get more and more -- the public appreciation of him has got wider. He's known around the world and so forth. What was that like for you? You're a mathematician, and you're also a gay man like Turing, and you come along and you write this book, and the recognition increases. So what was that like for you, Andrew, just to almost be vindicated, if you want to put it like that?

Andrew Hodges: [laughs] Yes, well I can't say it's in life's story really. Of course, it's not the only thing I've done. So my main career really has been in theoretical physics working with Walter Penrose, actually, who's a Nobel Prize winner. And I made some contributions to his ways of looking at physics. That being my main job, that and teaching mathematics.

Andrew Hammond: Twistor theory, is that right?

Andrew Hodges: Right. At Oxford University. So it's not that my whole life's been all about this, [laughs] but it is a fascinating thing, and of course I think what strikes everyone of course is the social/political change that's taken place. There's no question that Turing's become far more acceptable figure, because instead of being regarded as a very regrettable and not really nice to talk about end of his life, is now something we talk about as part of social -- developing social history, and beginning a whole change of attitudes which is now been very wholesale change in Western society. So that's really been the main change. Also true, or course, as I said that his universal machine's now in everyone's pocket, and they're all bleeping and clicking away like mad. But I'm not sure that's the reason really why he's not famous. I think it's more that it's become more acceptable to have all these things named after him and celebrating him. So that's really -- well, that's not for the -- that's for the public, you know, to decide, really. That's a very -- as a whole question itself really, I mean how people are regarded. How science is regarded, how history's regarded, how sexuality is regarded. It's a huge business, and I was just rather lucky to be in a very interesting point where all these things intersected.

Andrew Hammond: I think that your -- you know, your brother career and the main thing that you've done -- - the main things that you've done during your career, I think that they feed into the biography too. Because you know, I feel like you describe a lot of the mechanical -- a lot of the more technical parts of this enterprise in a way that I think is much more lucid than people that are maybe coming to it from a different perspective. So yes. I appreciate your contribution. And final question, Andrew, what was it like to be on stage at the Royal Albert Hall with the Pet Shop Boys to honor Turing? And Erin has put in here she can't find the video anywhere. Does it exist and can we view it?

Andrew Hodges: Well, the BBC -- well, there's not a video of it as far as I know. There are some photographs of it. But it went out as an audio-only concert on BBC Radio in July 2014. Well, that was a -- [laughs] well, I love the Pet Shop Boys, so it was -- I was a big fan of them. So that was something. I couldn't imagine it, I must say. And that was another of these extraordinary coincidences where the BBC had commissioned them to do something for their Promenade Concert Series in Summer of 2014. And they happened to know about my story, and called me, and were wonderful to work with. And they used my words, and so got it right, I think. And picked out some of the main points, and put extraordinary musical things in it. And yes, it's the only time of my life when I've appeared on stage in the Albert Hall. That's true [laughs].

Andrew Hammond: [laughs] Wow. That's a pretty incredible story. I've been singing "It's A Sin" pretty much all day in the build-up to our conversation. I'm a Pet Shop Boys fan as well. So it's been a real pleasure to speak to you, Andrew. Thanks for sharing your expertise and your insights, and I really appreciate it. [ Music ] [ Music ] Thanks for listening to this episode of "Spycast." Please follow us on Apple, Spotify, or wherever you get your podcasts. If you enjoyed the show, please tell your friends and loved ones. Please also consider leaving us a five-star review. Coming up next week, on "Spycast."

Speaker 1: So much can be said about social media and the things that folks, you know, video and post that can be used that are open source for great intelligence purposes like that. How many there are, where did they come from, and where are they going?

Andrew Hammond: If you have feedback, you can reach us by email at spycast@spymuseum.org, or on X at intlspycast. If you go to our page at theCyberwire.com/podcasts/ spycast, you can find links to further resources, detailed show notes, and full transcripts. I'm your host, Andrew Hammond. My podcast content partner is Erin Dietrick. The rest of the team involved in the show is Mike Mincey, Memphis Vaughn III, Emily Coletta, Emily Rens, Afua Anokwa, Ariel Samuel, Elliott Peltzman, Tre Hester, and Jen Eiben. This show is brought you from the home of the world's premier collection of intelligence and espionage-related artifacts, the International Spy Museum. [ Music ]