Bletchley Park

24:48A particular combination of settings used for a message is known as a key, and Enigma messages can only be deciphered using this key. At first, the messages are painstakingly decrypted by hand. The first successful breaks on German Army and Air Force Enigma traffic occur in late 1939, though the messages of the German Navy prove much harder to crack. Dilley Knox and his team rely on what are called cribs, essentially educated guesses about what parts of a message might say, which they then test against. Although the Enigma machine is incredibly secure in theory, human errors on the part of the German operators often introduce mistakes.

25:34For example, some start every message with Heil Hitler, or repeat routine weather reports. These repetitions give the British valuable clues to crack the code. Knox also develops a technique called rodding. A set of cardboard strips, or rods, representing the wiring of Enigma's rotors, are lined up against each other in different configurations to test commonly used words and reveal possible settings. Finding a combination that encrypts one of these simple test words can then be used to decode the rest of that day's messages. But despite some success in the early days of the war, it soon becomes clear that a much quicker method is needed.

26:19Not least because the Germans change the settings for Enigma every night when their clocks strike midnight.

26:30There is not much point in reading your enemy's hand if what you're reading is no longer relevant to what's happening in the field. So you need to be able to read your enemy's hand quickly so that it is operationally useful. In this challenge, the British codebreakers have a little help from their friends. Back in July 1939, knowing Poland would soon be invaded, Polish cryptographers revealed to the British and French that they had succeeded in breaking Enigma. In this task, the Polish codebreakers were helped by a machine known as the Bomber. Though their methods are now out of date, and the way the Enigma messages are encoded keeps changing, the Polish Bomber machine inspires Alan Turing and his colleague Gordon Welchman to create a machine they call the Bom.

27:25These electromechanical devices help to find the daily key settings of the Enigma cipher machine. They are Turing's most famous achievement at Bletchley Park, and a complete game-changer in the war. Alan Turing's invention of the bomb, the precursor of which was the Polish-born bomber machine, the first bomb arriving in Bletchley Park in March 1940, would have ultimately a transformative effect in terms of the way in which we were able to harvest Enigma-encrypted communications on a macro scale. So, for example, about 18 ,000 messages a day come 1944 and the D-Day landings. Think of a sort of black bookshelf, a giant throbbing black bookshelf full of soldered connections and wheels, an intimidatingly enormous contraption that had to be plugged and deplugged every time it was used.

28:24and instrumental in making it effective was this diagonal board which welshman came up with and that meant that the enigma codes and ways into finding the keys for that day the settings for that day could be reached within a matter of hours rather than within a matter of days which as you can see is crucial especially as the germans are changing their settings at midnight every day

28:56Named Victory, the first bomb becomes operational on March the 18th, 1940. Later that year, Turing authors a report detailing the methods he and his colleagues employed to break into Enigma. At Bletchley Park, this reference manual becomes known as the Prof's book. The BOM machines are primarily operated by members of the Women's Royal Naval Service, known as RENs, with other women being recruited from universities. Indeed, in many areas, women become a vital part of the Bletchley workforce, eventually accounting for 75 % of the staff. Members of the Women's Auxiliary Air Force and Auxiliary Territorial Service are employed here in roles ranging from dispatch riders to translators.

29:43You will recall the film The Imitation Game with famously Benedict Cumberbatch playing Alan Turing. In one of the promotional posters, there's a picture of him and I think four other men and Keira Knightley playing Joan Clark, this woman who was romantically connected briefly to Alan Turing. And it's somewhat ironic because actually the numbers in terms of the gender balance at the park was the precise opposite of that poster. So certainly by 1942-43, you had four women to one man approximately operating at the park. And I suppose there was a key difference in their roles. There certainly were women in the code-breaking teams, but it was a predominantly male affair.

30:29And that speaks to the times when it's predominantly men at university. It's predominantly men who are physics and maths professors. However, we know that there's a chronic manpower shortage across all services by really very early on. And we've got a recruitment crisis. And the answer is to enlist more women. And if you can't get them to enroll, then you can force them to enroll because it's a war. So you have female conscription.

30:58From April 1940, a shift pattern is introduced to keep the code-breaking efforts running 24 hours a day. Hardly anyone lives on site, so a steady stream of buses and other transport brings staff from nearby billets and requisition properties, including Woburn Abbey, a nearby stately home where many wrens are housed. When off-duty, personnel can take advantage of the wide range of clubs and activities, as well as dances and performances at Wilton Hall, a purpose-built venue near the main entrance. There is a library, a drama group, music and choral societies, and clubs for bridge, chess, fencing and Scottish dancing, as well as sports like tennis and cricket.

31:42In the early 1940s, a series of numbered wooden huts is built across the grounds to accommodate the expanding operation. Hut 11 contains the bomb machines, used to determine Enigma's daily rotor settings. Over in Hut 6 is the team working on breaking Army and Air Force Enigma messages. Once they have completed that task, they place their decrypts into a basket and use a broom handle to push it through a specially built chute to their linguist neighbors in Hut 3 for translation into English. Crucially, the personnel in one hut are not fully informed about the work of the other, maintaining strict security.

32:25With the bomb machines up and running, the team at Bletchley Park is now regularly cracking Enigma encrypted communications from the German army and Luftwaffe. This intelligence, known as ULTRA, plays a role in Britain's defense during the Battle of Britain from July to October 1940, allowing the RAF to anticipate some German operations before they unfold. But nearby, in Hut 8, Alan Turing and his colleagues face an even greater challenge.

33:02Despite the progress breaking the enigma messages of the Army and Air Force, the messages of the German Navy prove more challenging. In the ongoing Battle of the Atlantic, the German Navy deploys submarines in coordinated groups known as Wolf Packs, which attack Allied convoys at sea, sinking ships faster than they can be replaced. Frustrated by delays and limited resources, in October 1941, Bletchley Park's senior intelligence officials draft a letter to the very top A position now occupied by Winston Churchill, since Chamberlain's resignation around 18 months ago Upon receiving the letter requesting more staff and equipment to tackle the critical naval codes, the Prime Minister immediately responds with the directive, Action This Day Once again, resources and personnel pour into Bletchley Park, which is fast developing into a code-breaking factory.

34:00When the United States enters the war in December 1941 after the Japanese attack on Pearl Harbor, the scale of the Atlantic campaign expands dramatically. Cracking naval enigma becomes even more vital to protect American troops as they move across the ocean. The German Navy divides its Enigma communications into different settings or keys, depending on the type of operation. Two of the most important keys used during the war are known as Dolphin and Shark. Bletchley is able to break the Dolphin key, used by German surface ships and naval shore stations, without too much trouble. But in contrast, the Shark Key, used by German U-boats operating in the Atlantic, proves much more difficult.

34:48In February 1942, the German Navy adds a fourth rotor to its Enigma machine, and with it, the number of possible settings skyrockets. Before, the codebreakers at Bletchley Park were already facing 150 quintillion potential combinations. But now, with the upgraded machine, that number jumps to over 180 septillion. A similar number to the grains of sand on Earth, 130 ,000 times over.

35:24And that staggering increase in complexity occurs just as the war in the Atlantic reaches a critical point. Somewhere between 60 and 110 vessels were sunk every month for eight months in 1942. It's real carnage and there's grave concern and this is the one place where Bletchley Park isn't able to even deliver a chink of light, blocked out. And you can imagine the stress of that within Hot 8 and the likes of Alan Turing having to operate under very stressful conditions. What breaks the deadlock is a so-called pinch, a risky operation in which Allied forces board an enemy vessel to capture intelligence.

36:05On October 30, 1942, the HMS Petard carries out such a mission on U-559, a German submarine. And before it sinks, they get on and they manage to get out both an Enigma machine and officially a codebook, which will show them the way into the so-called Shark Key, this fourth rotor. And that's transformative. So by the end, I think it's November 1942, you're back in action, full speed ahead in terms of being able to predict where your wolf packs are going to be hunting your allied convoys. Because until that point, we're losing about 500 ,000 tonnage a month. But even as progress is made with the shark key, Bletchley Park is already facing another, even more complex enemy cipher used for the most secret communications of Hitler himself.

37:02In the early 1940s, the British Y stations began picking up strange radio signals that sound like unreadable gibberish. These turn out to be messages encrypted by the Lorenz cipher machine, used for the highest level communications between Hitler and his high command. Far more complex than Enigma, Lorenz is a much larger and more sophisticated cipher system, and breaking it becomes one of Bletchley Park's greatest challenges. It's interesting because the Lorenz machine, if you think your standard Enigma either has three wheels or four, the Lorenz machine had 12. It was far more sophisticated and it was this cipher encoded teleprinter communications.

37:49They were much longer. They went between the high command and all the way back to Berlin and ultimately to Hitler. So you're able basically to know what the Fuhrer is thinking and the extent to which he has a control over what his commands are doing on the ground. In the summer of 1941, a German operator makes a crucial mistake in resending a Lorentz encrypted message using the same key setting for both messages. Gletchley Park's chief cryptanalyst, John Tiltman, seizes the opportunity and manages the first break into a Lorentz message. Taking up the baton, Bill Tutte, a Cambridge mathematics graduate, begins to study the patterns in intercepted Lorentz messages.

38:35For weeks, he works alone in quiet concentration, prompting curiosity among his colleagues about what he is up to. But at last, his silence pays off. Using mathematical analysis, Tut deduces the structure of the Lorentz machine without ever having seen one. From mid-1942, intercepted Lorentz cipher messages are punched onto paper teleprinter tape and sent to a special new section at Bletchley where cryptanalysts manually work to turn streams of gibberish into intelligible German. However, by 1943, the German operators have adopted more complex encryption practices, making it almost impossible to break Lorentz using manual methods alone.

39:23The code breakers now need a machine, capable of handling vast volumes at speed The General Post Office, or GPO, is enlisted to help develop an electromechanical solution

39:40The result is a cumbersome but ingenious device that automates part of the process Nicknamed the Heath Robinson after the eponymous British cartoonist known for his drawings of overly complicated machines, it proves unreliable at high speeds To meet the challenge of improving it, engineer Tommy Flowers, working at the GPO's Dulles Hill Research Station, designs and builds a more advanced solution some of alan turing's thinking was involved but ultimately it is built by an individual called thomas or tommy flowers who is a humble general post office engineer and he builds it at personal cost he takes out an overdraft to help him fund this invention this creation it's built in dollis hill in north london in one of the post offices buildings and he's very understated he's Your original working-class lad done good.

40:42The result, which is known as Colossus, is the world's first programmable electronic digital computer. It would be fair to say that the Colossus is really your prototype first computer because it's programmable. What you have are thousands of vacuum tubes. They're actually valves. The first one, I think, had 1 ,600 of these vacuum tubes. And latterly, by the time of D-Day, the second one arrives on the scene and it's got about 2 ,400 tubes and it's about five times faster than the first Colossus that's operational. And effectively, those 2 ,400 valves replicate the pattern of an encrypted RENS machine as electrical signals.

41:30And to give you some idea of the scale of this, the Colossus machine could read 5 ,000 characters a second.

41:42Colossus arrives at Bletchley Park in January 1944 and helps the codebreakers to decipher the Lorentz messages in near real time. To give you an idea of just how understated Tommy Flowers was, the day his machine, his Colossus, achieves its first scientific miracle, he actually writes in his diary, Colossus worked, car broke down on the way home. So the thing is about Velocity Star is almost like this irony, it's the understated way in which it all takes place in the time, under the cover of darkness, shrouded in secrecy. The first Colossus is soon joined by others. A new section is set up to house these computers and the teams of Wrens operating them.

42:31By the last months of the war, the workforce at Bletchley and its outstations numbers around 9 ,000. The detailed knowledge gained by human and machine of enemy troop movements is particularly helpful on the lead-up to D-Day, the Allied invasion of German-occupied France in June 1944. You have two things that are game-changing deliverables for the summer of 1944. And one is a thorough awareness of the German armed forces and what they represented in the Normandy area in June 1944. Now, information that we had was hugely detailed thanks to information that was harvested by the code-breaking nexus.

43:13Now, that includes numbers of troops, vehicles, tanks, as well as maintenance and serviceable information. All sorts of information about where your enemy's at, where he's positioned. The other really valuable part of what Bletchley Park delivered prior to the D-Day landings was a clear confirmation that the German enemy high command had swallowed the deception structured into Operation Fortitude. So Operation Fortitude is this ruse that the Germans believe were going to land in Padakele, which is where they put the majority of their defensive forces to repel our invasion. Paddelkele is the very obvious place to land, of course, because it's the shortest distance between Britain and France.

43:54So when you're armed with not only a knowledge of what's happening on the ground in Normandy, but also the sure certainty that the Germans don't expect you to land in Normandy, that encourages you, gives you confidence. And remember, victory in war is partly born of good or high morale. Thanks to the misdirection of Operation Fortitude, key German forces are kept away from the real landing sites in Normandy. The successful D-Day landings on June 6, 1944, mark the start of the Allied push to liberate Western Europe from Nazi control. Over the following months, Allied forces advance across France and into Germany, leading to the German surrender in the spring of 1945.

44:40and the news is heard at Bletchley Park before the rest of the world.

44:59It is a night in late April 1945. Deep inside Block H at Bletchley Park, a team of wrens tend to the giant, glowing bulk of a Colossus machine. The room pulses with noise. A high-pitched whir comes from the reader as it feeds a looping ribbon of punched tape through optical sensors at an astonishing speed. The machine hums and clicks, its blinking bulbs lighting the faces of the women who monitor it. A young wren leans close to the machine, straining to make an adjustment, then shouts across the room to be heard over the din. It's always loud in here, always hot. But tonight, something feels different.

45:47The sense of pressure that has filled these rooms for so long is beginning to ease. It's in the way people glance at each other, the way they smile more readily. Even the newspapers, always a step behind what they know here, have begun to hint at the truth. Germany is collapsing. The end is coming.

46:12Then the door swings open. A wren rushes in, breathless, her uniform slightly askew, a small slip of paper clutched in her hand. It's over, she shouts. The war is over. For a moment, no one moves. Then one Wren lets out a loud whoop and reaches for her colleague's hand, and suddenly the whole night shift spills outside.

46:41They hurry across the gravel paths in their sensible shoes, skipping and shouting, hugging each other in celebration. Someone rushes to the supply closet and returns triumphantly, arms piled high with rolls of toilet tissue. In minutes, a tree on the driveway is festooned with white streamers, and the women dance around it as if it were a maypole. Then a voice cuts through the jubilation, a man demanding to know what on earth is going on. Everyone freezes as the senior officer, face furious, storms over. He reminds them that this is a classified site, and they still have work to do. The Wrens swallow their giggles.

47:24One of them slowly unwraps a wreath of loo roll from her head, and they make their way soberly back to Block H and the whirring Colossus. The celebrations have ended for now, but there will be far more to come.

47:46After the Second World War, Bletchley Park's vital role in breaking enemy codes endures as a closely guarded secret for decades. In the spring of 1946, GC and CS officially leaves Bletchley Park and moves to East Coat, northwest London. Four years later, the organization, renamed as Government Communications Headquarters, or GCHQ, relocates again to its current site in Cheltenham. At Bletchley, many of the wartime huts are left to deteriorate, while the thousands of men and women who worked there during the war remain sworn to secrecy. It wasn't cast as a woman's war in our nation's imagination, so women therefore weren't asked questions.

48:30all the girls or women who I worked with who operated at Bletchley Park and were part of the code-breaking nexus they don't remember being asked questions about their war because people didn't associate women with war even though women had been conscripted for the first time ever and that helps of course and it also helps that you don't really know what you were doing you were checking off crosses on a sheet of paper were you or maybe you were actually using your mass to do something a bit more exciting, but you don't really have a macro scale idea of what you achieved. And you didn't have a reference.

49:04You had some kind of vague job description that you worked for the Foreign Office, for example, if you'd been in civilian clothes or that you were Wren doing some administrative work in Buckinghamshire. So that doesn't put much pressure on people, does it? If you think nobody's asking you and you don't really know, so you're not really going to say anything. For decades, the public learns little of Bletchley Park's extraordinary contribution. Winston Churchill famously refers to the code-breaking teams there as the geese that laid the golden eggs and never cackled. In fact, in the early days after the war, the biggest leak threatens to be Churchill himself.

49:43Ironically, given that there was this sort of idea that young women might be garrulous, it's the men, and the men much higher up, who are more likely to endanger the secrecy of what we achieve at Bletchley Park. And that goes for Churchill, as well as anyone else. He's found it very difficult to write, as War Mount was, without mentioning a staggering achievement which he had backed allheartedly. He was compulsorily forced to edit much of his World War II volumes because, of course, they crowed about the achievements of Bletchley Park.

50:15For one of Bletchley's stars, Alan Turing, life proves much harder. In 1952, Turing is prosecuted for gross indecency related to his homosexuality, a criminal offense in the UK at the time, and undergoes chemical castration as part of his sentence. He dies two years later on June the 7th, 1954, at the age of 41 from cyanide poisoning. His death is ruled a suicide. It isn't until decades later that the government issues a formal apology for his treatment, and in 2013 he receives a royal pardon. Turing is today recognized as one of the most brilliant scientific figures of the 20th century. Eventually in the 1970s, a veil of secrecy begins to lift.

51:06A government-approved book titled The Ultra Secret is published in 1974 by former intelligence officer F.W. Winterbottom. The first publication to reveal the secret code-breaking work carried out at Bletchley Park, it brings public attention to the remarkable achievements of the code-breakers who begin to have the chance to tell their own stories. Efforts to preserve the site as a museum and heritage center begin to gather momentum. and in 1994, the chief patron of the Bletchley Park Trust, the Duke of Kent, opens the site to the public as a museum. Today, Bletchley Park draws a quarter of a million visitors a year.

51:49Some of them even pop by for refreshments at a local pub called Captain Ridley's Shooting Party. But Bletchley Park is not only a museum of code breaking and computing history. It is also a lasting tribute to the quiet heroes whose work helped shorten the war and shape the modern world of intelligence and cyber security. We won the war partly thanks to our ability to read our enemy's hand. I don't think it became decisive in terms of helping victory really until about 42, 43. Certainly, we are reading Enigma codes, encrypted codes from 1940. But that sort of pinch point where it helps us win the war was really from 1942 onwards.

52:32but we can't be complacent going forward about where our genius then is going to take us now because we all know that at any one time the enemy is looking to outsmart us and I think that's probably the takeaway of Bletchley Park that war is not just bullets and beaches and dead men and nowadays dead women it's actually something that's often invisible and unpredictable and arguably even more dangerous.

53:10Next time on Short History of, we'll bring you part one of A Short History of the Victorians. I think the appeal of the Victorians is they are the germ of the ideas that we live with now. And a lot of the debates that we have now, you can find an earlier incarnation in the 19th century. But they're also just different enough to be fascinating. With their corsets and their funny gloves and hats and veils and rules about everything and anything. So I think a lot of people see them as modern enough to be relatable, but also strange enough to have a nostalgia for. That's next time.

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