>> Production of "Breaking Enigma: a World War II Game Changer" has been made possible by... Additional support was provided by... ♪♪ ♪♪ ♪♪ ♪♪ >> Bletchley Park is a story that, of course, for many years was kept secret.

Actually, there was a fantastic story here about people being brought together, most of them ordinary people with ordinary backgrounds, brought together and did extraordinary stuff in terms of helping the war effort.

>> The fact that people don't talk about Bletchley, it's impressive.

But, also, it's no more than you'd expect from them.

They'd been very carefully briefed coming into this organization.

They mustn't breathe a word of what they do to anybody.

And as far as the people working here were concerned, that's going to be in place for as long as they live.

>> It was the... the whole atmosphere in the country at the time, bearing in mind that, um, we were at war and everyone in the country was geared up to do what they could to defend the country.

It was a universal atmosphere, no question about it.

We all knew that we should do something to stem off the invaders.

♪♪ ♪♪ >> [ Speaking in German ] [ Cheers and applause ] ♪♪ ♪♪ [ Cannon fires ] ♪♪ ♪♪ [ Siren wailing ] >> We shall fight on the beaches.

We shall fight in the fields and in the streets.

We shall defend our island, whatever the cost may be.

[ Explosion ] ♪♪ [ Explosion ] >> ...interrupt this program to bring you a special news bulletin.

The Japanese have attacked Pearl Harbor, Hawaii, by air.

>> The United States of America was suddenly and deliberately attacked.

[ Indistinct conversations ] [ Hitler speaking in German ] ♪♪ [ Hitler continuing in German ] [ Men shouting in German ] >> It all began with a madman, who quickly overwhelmed Europe.

>> We have Hitler, and the way he put himself across -- Hitler is the leader.

Everybody says "ja," says "yes" to Hitler.

And then the ultimate -- how Hitler saw himself.

I mean, here he is, right out of a Wagner opera.

He is literally the knight in shining armor ♪♪ >> [ Speaking in German ] >> The general feeling was that we had been unjustly treated.

And so he used that ressentiment.

Um... "I am the one who will bring your proud back.

And I'll be the one who takes the injustice, um, away from you."

[ Group singing in German ] He was welcomed by the majority as a leader who takes us out of the misery after the First World War.

[ Hitler speaking in German ] >> Just days after Germany invaded Poland, officially starting World War II, work began ramping up at a top-secret location 50 miles northwest of London, England.

Great Britain's top mathematicians, scientists, classicists, and linguists were working inside this oddly constructed late-19th-century mansion in the small town of Bletchley in Buckinghamshire.

Ordinary British citizens The picturesque area is known as Bletchley Park.

English people with varied backgrounds came here because their government asked them to do something that most thought was impossible -- the solving of one of the world's most difficult puzzles.

This wasn't a game, however.

Unscrambling this riddle was a matter of life and death.

Solutions were needed -- sooner rather than later.

>> At the beginning of the war, there are 185 people working at Bletchley.

And they're a mix of pre-war expert cryptanalysts who've been in this field for many years, support staff, and new arrivals, as well, mostly from Oxford and Cambridge Universities.

>> In 1939, Bletchley Park stretched out over 58 acres.

Many nondescript buildings and huts were acquired or built soon after the war began with Germany.

>> Bletchley Park is obviously a very heavily secured site, but what's interesting is, it's almost hiding in plain sight.

It's not in an isolated location.

It's on the outskirts of a fairly large town.

All the locals know that there is an enormous government organization at Bletchley Park.

They just don't know what's going on there.

>> And it had to stay that way.

The future of England, and maybe the world, depended on it.

>> The whole country understands in a basic way that secrecy is essential for the war effort.

>> The top-secret work at Bletchley Park in 1939 and 1940 focused on a clunky, wooden-cased, typewriter-looking apparatus -- Germany's Enigma machine.

The Enigma was how the German armed forces and senior staff formulated all their secure messages and battle plans... encryptions that would then be sent around the globe.

Germany believed that no one could ever decode and read transmissions created by Enigma, especially if they had to do it by hand.

In 1940, the British desperately needed to know their enemy's plans because England was on the verge of losing the war.

Some early code-breaking successes led to optimism.

>> The Germans know that the Allies are going to attempt to break their ciphers.

Everybody does this sort of signals intelligence on this radio interception.

But they have a good, modern machine cipher in use in Enigma, and they come to the same conclusion as people on the Allied side did early in the war -- that this probably isn't gonna be breakable just because of the vast number of permutations you can achieve through the design of the machine.

>> A possible 103 sextillion combinations, to be exact, for each Enigma message composed.

Adolf Hitler was betting that Enigma's messages could never be deciphered.

What the Nazis didn't understand was the concept of teamwork when it came to problem solving.

>> In a fascist state like Germany, knowledge is power.

There are many different agencies competing with each other, competing for political prestige most of the time, rather than focusing on the efficiency of their work, and you don't have the ability to centralize operations in the way that you do on the Allies' side.

And you can never give the people involved the freedom to innovate, because that would pose a political threat to the regime ultimately.

>> There are two main strands in the Bletchley Park story.

One is about intelligence and how that works, and the same thing in terms of technology and computery.

>> For the British, breaking their enemies' diplomatic or military codes was not new with the arrival of another world war.

>> At the opening of World War II, Britain has a code-breaking agency already.

It's existed since 1919.

It's called the Government Code and Cypher School, and it had been working down in London through the interwar period with about 150 staff, and it moves to Bletchley shortly before war breaks out in August 1939.

>> An Enigma machine comprises a keyboard and a set of 26 lamps, each corresponding to a letter.

These components are connected by a plugboard and a rotor set, allowing the wiring to be scrambled.

When a letter is typed on the keyboard, a different letter illuminates on the lamp board.

In this way, a message can be enciphered.

The rotors move when a letter is typed, resulting in a different scrambled wiring.

Because there are millions upon millions of ways of setting up the rotors and plugboard, an enemy codebreaker cannot hope to guess the correct setting or test them all.

However, a person who knows the correct setting, called a key, can set the Enigma up correctly, type in the enciphered letters, and restore the original message.

>> Here we have all of the different Enigma machines that were used by Germany, from the three-rotor that was used by the army, to the four-rotor that was used by U-boats.

The German navy was positive that nobody could read these codes.

Germany believed they could never be broken, so they always relied on the Enigma machine.

They were certain that it was infallible.

The only way these codes did get read was not breaking the code, but capturing a codebook on a German sub.

Not a lot of German subs were captured, but -- And they all had plans to scuttle them.

Codebooks were printed in red water-soluble ink, and there was a bucket of water in the code room, and a codebook only had to be dropped in the bucket and it all dissolved.

One codebook was taken off a submarine, gave them the key into the Kriegsmarine Enigma.

And then they knew where submarines were going to be.

Britain a year into the war was reading everything.

Defeating Rommel in North Africa was done because the Allies knew when the supply ships were leaving Italy, they knew the routes they were taking.

The Battle of the Atlantic hinged on this four-rotor machine.

>> A Coast Guard cutter attacks a prowling U-boat.

One small skirmish in the long Battle of the Atlantic.

[ Explosion ] [ Morse code beeping ] >> Germany's neighbor, Poland, was already working on reading German army and air force communications prior to the Nazis taking control in 1933.

>> The Polish contribution to breaking Enigma is absolutely essential in the beginning, because the techniques the British are using at Bletchley Park to achieve their first breaks of Enigma are the same as were developed in Poland.

And there are three Polish cryptanalysts who succeed in reading Enigma ciphers beginning in about 1932, and they keep that effort going right up to nearly the outbreak of war.

The Polish fully anticipate that Germany is poised to invade, and this is why they take the decision to share their information with the British and the French, as well, in July 1939.

So by the time the Government Code and Cypher School comes to Bletchley Park, the team working on Enigma have good information about the system in use as the Germans use it, and they have techniques which they anticipate will work to break it.

And at that point, the problem is a matter of resources and people power.

And this is what the British do for the first six months of the war -- apply their superior resources, and they succeed as expected by the early part of 1940.

♪♪ >> By the end of June, 1940, mainland Europe had been conquered.

The British were expecting a German invasion of their island at any time.

England was on the ropes.

Tons of shipping and much-needed lend-lease supplies bound for England from the United States were being sunk in the North Atlantic by German submarines, known as U-boats.

[ Man speaking in German ] ♪♪ [ Explosion ] ♪♪ [ Explosion ] ♪♪ Top-secret Bletchley Park, now code-named Station X, needed to deliver a win.

>> It's a 24-hour, seven-day-a-week operation.

This place never stops and the pressure is immense.

Everybody here knows, even if they don't know precisely what their work is or what the output is ultimately, where the intelligence is going, they know that speed is of the essence, that the more they can do here, and the quicker they can do it, the more likely they are going to be able to save Allied lives.

>> The workforce at Bletchley Park was diverse.

A mix of intellectuals, problem solvers, and chess masters worked alongside secretaries who could type 60 words a minute or clerks who excelled at filing.

>> This division of labor means that you can bring in not geniuses from the universities.

You need them, as well, to pioneer some of these techniques.

But most people working at Bletchley Park are perfectly ordinary people of average intelligence from ordinary backgrounds.

75% of them are women, and they fill roles in all parts of the organization, other than the very highest levels of management.

The difficult balancing act for the management is to give people a sense of the contribution they're making, without giving them too much of the picture of precisely where their intelligence is going.

But they're able to walk that tightrope quite effectively.

>> The work at Bletchley Park was mentally grinding for everyone.

Those overseeing the code-breaking program recognized early that their mind-powered train would eventually derail if employees at Bletchley didn't blow off steam.

Keeping up the esprit de corps at Bletchley Park included activities ranging from tennis, to bicycle riding, to peaceful walks by the lake that fronted the mansion... any distractions that got codebreakers' minds off letters, numbers, and codes.

>> There's a great culture that builds up at Bletchley.

A large number of recreational activities for the staff to take part in that are naturally brought from the universities by, um, a very well-educated and a cultured staff from those backgrounds.

The management at Bletchley absolutely understands that their staff, if they're gonna work efficiently and recover from the strain of the work, they need to have good, quality time off.

So recreation is vital.

They provide facilities for that.

They encourage clubs and societies to be founded and run in off-duty hours.

They maintain the site as a place where people can relax.

There's an area here that isn't built over near the pre-war formal gardens and around this pre-war lake, which is maintained as a space for people to relax.

So that's absolutely understood by the management.

They know their workers are only going to work efficiently for long periods if they are given time to unwind.

>> We did have facilities for recreation, such as a Bach choir; a madrigal society, which I was a member of; a drama group, a gramophone club, um, a fair amount of sport, uh, tennis and, um, darts and all that sort of thing, you know, table tennis, so on.

So, um, from that point of view, um, we were really very well looked after.

>> From the start of the war, people living and working in -- in huts, you know, I'd term as glorified garden sheds, you know.

They're not much more.

And yet they were doing fantastic, cerebral work in those facilities.

And as the war progressed and the place expanded, more and more facilities were made for them.

But it was still pretty rudimentary.

They were living in wartime conditions.

They were on rationed food, et cetera, et cetera.

So the fact that they did what they did in those -- those conditions is quite extraordinary when we look back on it.

>> "Extraordinary" also describes the groundbreaking work at Bletchley Park in 1940 by a 27-year-old British mathematician named Alan Turing.

Turing was a visionary, and one of Great Britain's most exceptional thinkers and innovators.

Alan Turing's team initially broke the Enigma code by hand, but Turing believed using a machine to decode messages would be much more efficient.

This was especially true for Enigma's most challenging messages to solve -- those that belonged to the German navy, or Kriegsmarine.

>> Turing is brought in to join a team working on the problem of the German Enigma cipher.

It's only about a dozen people at that point working on this system, essentially as a research project, but they have good hopes of success because of information they've received from Polish intelligence before the war.

So Turing is part of that team essentially doing theoretical work for the first six or so months of the war.

During that period, he comes up with the basic design of a machine known as the Bombe, which is "bomb" with an E on the end, which is not quite a computer, but it is a cryptanalytic machine which they anticipate will enable them to break Enigma ciphers.

So it doesn't take too long before the Allies are into the German's most secure cipher systems.

>> Turing's Bombe machine, housed in a hut at Bletchley Park, was designed to automate and speed up the Enigma code's breaking.

Turing set his sights on Germany's most complicated and problematic encryptions.

The Bombe machine was up and running.

[ Machine whirring ] ♪♪ >> And the way it works, put very simply, is that it's like lots of Enigma machines wired together, and it allows you to test the letter pairings, which you observe when you have an intercepted message, and compare that to your assumption about what the message really says in the plain text.

So the Germans have a habit of sending very guessable messages.

They will start a weather report with the word "weather report."

They will sign off a message by saying "heil Hitler."

So you get these what are known as cribs that allow you to start breaking into a message.

And the Bombe machine speeds up your process of testing cribs and allows you to deduce a large part of of the cipher key.

At that point, Turing moves on to an even tougher problem, which is specifically the Enigma ciphers used by the German navy.

Because the German navy has a better awareness of communication security and has better procedures in place, their ciphers are tougher than those of the German army and air force, even though the machine is no different.

And this is what Turing takes on, in his own words, because nobody else was doing anything with the problem, and he could have it to himself.

He sets up a team in hut eight, and this becomes the section which breaks naval Enigma ciphers from the middle of 1941.

They're finally successful.

>> What tragedies... >> British Prime Minister Winston Churchill supported the efforts at Bletchley Park, Alan Turing's work, and the intelligence game from his chaotic war rooms in London.

Churchill toured Bletchley Park early in the war.

The prime minister, high-ranking British military leaders, and England's War Cabinet were briefed on Enigma's results.

Churchill's team was supplied with the latest German transmissions, which, thanks to Alan Turing's groundbreaking Bombe machine, were now regularly being decoded at Bletchley Park.

>> Churchill is an enthusiast for intelligence across the board, and for secret operations and irregular warfare.

Um, so he's very interested in the product of Bletchley Park as soon as it starts to kind of land on his desk.

At one point in the war, quite early in the war, he asked to be fed with all of the output of Bletchley Park.

And this is quite a difficult request, because even at that point, they're generating hundreds of decrypts from German ciphers every day, let alone all of the other countries they're eavesdropping on.

So a system is put in place where a selection of the most important messages are picked out and they're placed in Churchill's red box and end up on his desk every morning.

And he's able to sift through them and get a picture of how the war is going as the Germans see it.

At points in the war, he intervenes personally to make sure that the codebreakers here have the resources they need to do their work.

And he's a great advocate for that at the end of the day.

It doesn't mean Churchill is necessarily the most important user of intelligence.

He tends to use it as a stick to beat his commanders with, to win arguments with them, rather than maybe be a more measured analyst of what the intelligence is telling him.

But there's plenty of other people in the British system who are much more capable of drawing the right conclusions from the intelligence they're receiving, and sort of counterbalancing some of the ideas that are coming out from Churchill.

♪♪ >> Any military details gained from breaking Enigma at Bletchley Park, or Station X, were given the code "Ultra."

>> The decision as to how you use intelligence isn't really Bletchley's to make.

They report facts, and it's important for the kind of intellectual rigor of Bletchley Park that they don't introduce their own interpretation into the information they're reporting.

So it's their job to give the facts about what the enemy are doing.

It is up to the customer to decide how you act on that information.

>> The customer is the top leadership within the British military.

♪♪ Intelligence reports were critical to the Allies' success as they began fighting back in World War II.

As the war progressed, Bletchley Park's eavesdropping on future Axis plans extended to the Middle East, Singapore, and Australia.

With guidance from the United States, now in the war following Pearl Harbor, Bletchley Park was also working diligently to help read and break the Japanese diplomatic code, referred to as "Purple."

So-called listening posts were set up all over the United Kingdom.

The Allies were now reading their enemies' most important coded messages.

The key was not to let the Axis know that.

>> The idea that you have to be careful how you use the intelligence in order to not give the game away to the enemy about the scale of your code-breaking -- There's truth in this, very rarely stops the Allies from using what they know.

>> I was thrown in at the deep end with a delightful group of people headed by... >> English teenager Betty Webb joined the British Auxiliary Territorial Service with about 300 other women in 1941.

Betty was 18.

>> I learned German as a child.

>> In 1937, a then 14-year-old Betty Webb was studying abroad in Germany.

Betty had no idea that picking up the German language then would play a huge role in her future.

>> I went on an exchange visit to a family, to a little town called Herrnhut in Saxony, near Dresden.

And I spent three months there actually living with a German family.

I didn't know enough German to participate in exams or anything like that, but I did improve my German, I think, a bit while I was there.

But, of course, it was the period when the Nazi regime was building up and, um, the family were very unhappy about it.

>> In 1941, a British intelligence officer noticed on Betty's résumé that she knew the German language.

>> Because I'd put on my CV that I spoke German, I was sent off to London to be interviewed by an intelligence officer, and that is how I came to go to Bletchley.

Obviously, the intelligence officer was trying to find out whether I had enough up here to be sent to Bletchley, and the conversation was rather on the lines of -- it was in German -- um, communication.

And he said, "Here you are.

Here's a railway warrant to Bletchley.

Get yourself to Euston."

I'd never heard of Bletchley and I certainly didn't know what went on there.

So I was completely in the dark, as most of us were at that stage.

My parents didn't know where -- Nobody's parents knew where we were.

>> Women filled roles at Bletchley Park right across the organization, and some rise to positions of significant responsibility and become real experts in their field... whether that's in actual cryptanalysis or in, um, interpretation of the decrypts.

It's not really correct to say there is women's work and men's work at Bletchley Park, 'cause women are also working in very senior and responsible roles.

and really gender and also rank and age don't really figure in how Bletchley Park operates.

>> All those who worked at Bletchley Park were sworn to absolute secrecy.

Everyone had to sign a forbidding government document.

>> It was late in the evening and we were taken straightaway to civilian billets until the following morning, when we were given the Official Secrets Act to read and sign.

I can tell you it was very long and rather frightening in a way.

We were then told that we must not divulge anything that we saw, read, or heard within Bletchley.

>> Betty Webb's work at Bletchley started as clerical, transcribing messages from the German military police, army, and SS.

Betty filed the information on index cards.

>> I was in the mansion in one of the rooms upstairs and I was helping, um, an officer who was... [ Chuckles ] He used to write things out.

This is the stuff that had been decoded and translated.

And he was writing it out and he wanted it typed out.

>> German Enigma messages were arriving at a frenetic pace.

>> In the region of 10,000 a day.

We didn't do them all.

There were other departments who had the same job.

>> By 1943, 73 of Alan Turing's Bombe machines were up and running at Bletchley Park.

♪♪ The British shared their newfound intelligence gathering with other Allied nations, especially the United States.

>> American and British sharing of intelligence goes back to early 1941.

So before the US had actually joined the war, four American cryptanalysts visit Bletchley Park, and they're shown the whole operation here... and eventually, even the most secure parts of it, such as the breaking of Enigma.

>> Following the Pearl Harbor attack, intelligence sharing between America and England significantly increased.

>> When the US joins the war, an agreement is reached that Britain takes the lead on German code-breaking, and America takes the lead on Japanese code-breaking, because that had always been their expertise.

About 250 US Signal Corps personnel are sent to work at Bletchley Park, and they make an outsized contribution because they are very carefully selected from the most skilled mathematicians and interpreters.

The British are kind of worried that the Americans will come in and throw their weight around and try and take over the operation, but they find that they're actually remarkably modest, and their attitude on the American side is, "What can we do to help?"

So the Americans contribute to all aspects of the operation at Bletchley.

And similarly, the intelligence from Bletchley Park is being fed to American commanders on exactly the same basis as British commanders.

[ Typewriter bell dings ] >> Our day consisted of an eight-hour shift.

>> In December of 1941, Julia Parsons was living in Pittsburgh, Pennsylvania, 3,676 miles from Bletchley Park.

>> When I first heard of Pearl Harbor, I was driving down Route 30 to deliver a package to a friend whose birthday it was, and I heard that Pearl Harbor had been bombed, and I had no idea where Pearl Harbor was.

I had never heard of it.

I had no idea it would have such a tremendous impact on my life.

>> Americans started joining the war effort immediately following Pearl Harbor.

First, the men signed on, and then the women.

>> All the boys in my class in college were long gone, and there was nobody left.

All my friends were gone.

Everybody was happy to do something.

It was the most patriotic time I have ever lived through.

>> As in England, American women could not serve in combat, but offered to help in every other facet of the war.

In 1942, Julia Parsons wanted in, too.

>> The Marines and the Coast Guard weren't taking women at that point, but the Navy was.

I saw in the paper that they were accepting women in the Navy for the first time, and you could get a commission if you had finished college and were, uh, available to go.

And I was, and I did.

>> On April 13, 1943, Julia Parsons was shipped to Massachusetts for officer training school -- a first-time offering for women.

>> The Midshipmen's School was at Smith College in Northampton.

We lived in dormitories.

It was very strict, very Navy, very, uh... just as if we were men.

>> The coursework at Smith College involved cryptology, physics, and ship identification.

Following graduation, Julia got her orders.

>> I don't really know how I was assigned to Washington, D.C.

We were not given any choice.

We were not talked to in advance.

They just gave us our orders and we followed them.

>> Julia Parsons reported to the Mount Vernon Seminary in Washington, D.C., specifically to the Naval Communications Annex.

>> I have no idea how the Navy or anyone else picks a codebreaker, but I noticed that everybody in our office was either a math major -- The top officers were all mathematics professors from colleges all over the country.

I guess you have to have a mathematical mind, because the mathematics does come in there, and certainly into the Enigma machine.

>> Julia Parsons landed in a section code-named "Shark."

>> I got to Washington, D.C., and the Navy immediately shipped a busload of us out to the Communications Annex, where I worked the entire span of my career.

We were all put in a room and someone came in and said, "Does anybody know German?"

And I said -- I raised my hand and I said, "I had two years of it in high school."

And that was it.

I was the only one who had had any German.

So they immediately shipped me to the section called OP-20-G, which was the German submarine traffic.

U-boats, they called them.

England had gotten so overwhelmed that they finally asked if the United States could take part of the code work, and they were happy to do it.

And we did.

And this -- All of the units at the Communications Annex used the Enigma machine.

We did not do the translation.

There was a section that did all the specific translation.

>> Like Betty Webb in the UK, Julia Parsons in Washington, D.C., signed a document similar to England's Official Secrets Act.

>> Very top secret.

We were threatened with everything under the sun if we ever divulged anything, and people kept saying women can't keep a secret, and we proved to them that we could.

We knew that it was secret because there was a double barbed wire fence around the communications annex, and Marine guards patrolled between the two fences 24 hours a day.

We were warned to never say anything.

We couldn't take anything in or out.

No packages, no cameras, no -- Nothing like that were permitted inside.

My primary job was to learn how the Enigma machine worked.

>> German messages arrived at the communications annex in Washington, intercepted from U-boats patrolling America's east coast and the North Atlantic.

>> Well, we got one that did come out.

We had broken the traffic for that morning or afternoon or whatever until the wheel order was changed again or the setting was changed.

So it was very frustrating when we did finally break the day's traffic, we were just so excited.

It was almost like Christmas for us when things did work out.

>> Many communications intercepted came from specific German U-boat radio operators.

Julia Parsons got to know some of them from their personal messages.

>> There's one thing about sinking a submarine, and there's another thing about killing people.

And the killing people was what I felt really bad about.

It was... a personal feeling that these men were only doing their duty the same as we were doing.

They probably didn't want to be there any more than than we wanted them there.

But nonetheless, it was there, and I guess that is war.

I know that's war.

And it was -- I felt very, very, very badly about the one who had just had a son, and his submarine was sunk.

And I thought, "That son will never see his father."

And it was a just a very poignant feeling, which, of course, nobody else talked about.

♪♪ >> Success at Bletchley Park in England and Washington, D.C., depended on individual skill and the ability to work as a team.

>> Everybody was compatible.

I don't think we had any flare-ups among any of the workers.

The women were all -- Our office was all women.

We had three officers and three secretaries in our office.

Everybody was very sober, serious.

>> Back at Bletchley Park, in England, Betty Webb was handed a new assignment as the war progressed.

It involved turning her attention from Germany to the Japanese and the war in the Pacific.

>> Somebody discovered that I was good at paraphrasing, and that meant reading decoded and translated Japanese messages.

I don't speak Japanese, and I didn't have to decode them, but I did have to paraphrase them for onward transmission to where I know not.

>> In January of 1944, another innovation arrived at Bletchley Park.

It was called Colossus.

English engineer Tommy Flowers is credited with its design and building.

Colossus is considered the world's first electronic digital computing machine with programmability.

It delivered the fastest decryption of Enigma messages yet.

>> Colossus is a computer.

It's designed to deal with a completely different system, the Lorenz cipher used by the German High Command.

It's a fundamentally different system from Enigma, much more complicated.

And so Colossus is developed to deal with this problem.

Because of its architecture, because it incorporates about 2,500 valves and it implements digital logic, Colossus, when it arrives at Bletchley, turns out to be much more versatile than really the designers had ever intended.

And this is when we can see that you make the leap from a single-purpose code-breaking machine to a computer.

>> Bletchley Park recruited 273 women to work the 10 Colossus machines, which eventually operated here.

The decoding of top-secret German and Japanese military messages continued at Bletchley Park for the remainder of World War II.

Neither Germany nor Japan ever found out their secret military messages were being read.

>> Each hour and the enemy's hedgehog defenses are ahead.

This is the supreme moment of invasion.

>> One of Bletchley Park's major code-breaking successes was the massive Allied assault on June 6, 1944, in Normandy, France.

The landings would not have succeeded without German intelligence being intercepted and decoded at Bletchley before D-Day.

The breaking of the German Enigma code and the Japanese code saved many lives.

Allied planners could now anticipate the plans of both their primary adversaries.

>> By the end of the war, the number of people who were aware of what's going on at Bletchley in a way that German ciphers have been broken on a large scale is certainly a few thousand people.

It includes all the senior Allied commanders, army, naval, and air commanders, their intelligence staffs, everybody involved on the special radio links, sending information out to commanders in the field, people at the intelligence agencies in London and in Washington, and obviously everybody or a very large proportion of the staff working at Bletchley Park, as well.

They all know the basics of Allied code-breaking.

They all know they have to keep it absolutely secret, and that's what they do.

>> Teamwork wins wars.

>> General Eisenhower actually sends a message to Bletchley Park at the end of the war, thanking them for their work and stating that through the intelligence they'd provided, they'd immeasurably eased the strain on Allied commanders and they'd saved thousands of British and American lives.

>> Our enemy in this campaign was strong, resourceful, and cunning.

But he made a few mistakes.

>> What surprises people about Bletchley is how large the organization was -- almost 9,000 people.

How ordinary, really, most people working here are.

How there was a place here for people from all genders and backgrounds and all levels of intelligence, that the vast machine which is built up here requires people of all kinds, with a vast range of skills.

I think that's fascinating.

>> Toward the end of the war, when the Germans knew they were losing, they got very careless.

And that was -- that was one of the ways in which we finally did finish the German submarines.

What made it easier for us to break the code was the U-boats appearing on the surface to recharge their batteries, which they had to do every so often, depending on how long they had been underwater.

And during that time, they had missed all the control's messages that came, and they would then radio back to control and say, "I have missed messages, say, 289 through 314," or whatever.

And then control would repeat the messages that they had sent to everybody else a day or two before.

>> Betty Webb and Julia Parsons' contributions during World War Two remained undisclosed for many decades.

Ultra, the decoding of Germany's Enigma messages, was the most significant secret of World War II after the atomic bombs.

>> There are a couple of reasons why the secrecy is maintained after the war.

The most immediate reason is to not give the Germans a potential propaganda victory and not allow them to make the argument that, like they did after the First World War, that they'd lost the war through some underhand means on the part of the Allies.

Later on, though, of course, we're heading into the Cold War.

>> I finally told my husband one night when we were all sitting out on the patio with some neighbors, and he asked me, just the neighbor asked me what I had done during the war and I thought, "You know, it's been so long, and it's all out in the open now anyway."

I still had a difficult time talking about it.

I didn't know that it had been declassified.

It was almost like it was a forbidden subject and I should never talk about it.

Plus, in the meantime, it was easy to keep it a secret because nobody asked.

Nobody remembered that sort of thing for years and years.

It wasn't even discussed.

I loved being in a secretive occupation, I will say.

It was thrilling.

It was really nice.

Everyone thought I had a desk job, which I did, but it was not a desk job as they had in mind.

>> My father had been in the army in the First World War, and I think he knew better than to ask.

I mean, they obviously must have questioned it amongst themselves, but they never bothered me with it, fortunately.

>> They kept that secret then for 30-odd years before it was allowed out.

And for many of them, it was still -- you know, went against the grain to talk about what went on at Bletchley Park.

But gradually over the years, they've got used to it.

But they are so proud of what they did, and now they can talk about it.

♪♪ >> Today, the past and present meet in a modern exhibit at Bletchley Park.

Artificial intelligence, or A.I., is now a part of the 21st century, and there's no going back.

A.I.

and the breaking of the German Enigma code at Bletchley Park aren't exactly foreign to each other.

>> During World War II, Bletchley Park was a hub of technological innovation, and three of the people who worked here went on to become early pioneers of artificial intelligence.

So those are Alan Turing, Jack Good, and Donald Michie.

We have in the exhibition a big kind of cascading timeline which goes through the middle of the exhibition and looks at the development of artificial intelligence.

And while at Bletchley Park, we weren't using artificial intelligence -- that came more towards the '50s -- one of the first things in the timeline is the invention of radar in 1935, because it started the idea of machines talking to each other and what that could create and what could come from that.

So a lot of the work here, Bletchley Park is often thought of as one of the birthplaces of computing.

And that's kind of the foundations of the theory which comes to A.I.

One of the reasons that we wanted to have the exhibition about artificial intelligence here was to engage a new audience who might not know as much about Bletchley Park's history or World War II or have some different interests, as well.

So the exhibition very much looks at artificial intelligence and how it's developing in our everyday lives and the opportunities and the risks that come with that.

But we always draw it back to what was happening with the work from Alan Turing and the others, as well.

>> We start off talking about these people who started their business at Bletchley Park, and then take it very quickly through to today and why it's important.

And there's always, you know, comparisons you can look at in Bletchley Park story.

The reason that the codebreakers here were often able to break into German or other Axis networks was because of human failure and operators.

Well, that's no different today.

You can break into modern-day computing security because people make silly mistakes.

You know, you put the man in the loop, then things start to go wrong.

♪♪ >> Bletchley Park is where people from all walks of life were handed the mission of solving a puzzle that was thought to be unbreakable.

That's where the Germans thought.

And the Japanese, too.

Betty Webb in England and Julia Parsons in America employed brainpower to help win World War II.

It all began here at Bletchley Park, where incredibly educated minds, alongside just ordinary people, helped turn the tide of World War II without ever pulling the trigger of a gun.

>> It's very difficult to quantify the contribution of Bletchley in terms of how many lives it might have saved or how much it might have shortened the war by, because these hypotheticals are just very difficult to work out.

We can never be sure.

But the contribution of Bletchley certainly very substantial.

I think if you took Bletchley Park out of the equation and imagine the Allies don't break high-grade German ciphers, you would really be looking at a completely different Second World War in the sense that the Allies would have to approach many of their problems completely differently.

They'd have been in the same situation as the Germans, where they're in the dark about the enemy most of the time, and they're almost having to fight with one hand held behind their back because they don't have the intelligence they need.

But as it is, the Allies do know everything they need to know about the Germans.

They're able to put plans in place, knowing that they will succeed.

They're able to risk their soldiers' lives and take those tough decisions, knowing that their sacrifice won't be in vain because they know that their plans will work, and that is an incredible advantage for the Allied commanders.

>> Admiral Doenitz, who was the head of all German control, kept saying, "No, impossible.

They could not possibly read our messages.

They cannot read the Enigma machine.

There is no chance there."

And he denied it to his dying day.

>> The Germans during the war never know about scale of operations at Bletchley.

They understand the allies carry out radio interception and have codebreakers in some form, but they never grasped the scale of what's going on, and they never grasp how successful the Allies are.

So the Germans never hear of the place.

>> I'm glad I had -- I was able to help with it.

I didn't know what I was doing at the time.

But this is the strange thing about being in an establishment where you can't talk about what you're doing.

It's only much later when you can piece things together.

>> At one level, Bletchley Park legacy is about how the intelligence communities operate today.

This place scaled up from, essentially, a cottage industry to an intelligence factory at the height of the war, and the processes, procedures, structures that were put in place to run this place endure today.

On the technology side of things, the people who are working here, the likes of Alan Turing, were pushing the boundaries all the time and creating processes, procedures, and machinery to help do the job here more efficiently, quicker, and better.

The relevance to today's audiences is about recasting the story all the time.

It's about telling it with connections to how they think, what they do, what their knowledge is.

And on the intelligence business, it's quite easy.

You can see uses of intelligence in modern-day conflict, whether it's Gaza or Ukraine.

For the computery, it's about tracing the DNA from what started here, one of a number of places where modern-day computery he started.

>> Despite the fact that I'm sad that we had to have a war, but I'm very glad that I was involved in it, because as far as I'm concerned, it's been a very interesting life for me.

>> In terms of our ongoing mission, we're sat in one of a number of wartime buildings that we have here.

Our job is to preserve these, open them up for the public so they can come and see where things happened.

Bletchley Park is renowned for being a place where fantastic stuff went on by a group of people who weren't recognized at the time, but now we know what they did and how important it was.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ >> Production of "Breaking Enigma: A World War II Game Changer" has been made possible by... Additional support was provided by... ♪♪ ♪♪