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Breaking the Enigma Machine

When we think about the defining locations that helped to shape World War II, we’re almost spoilt for choice. Normandy, North Africa, Okinawa, Midway, Pearl Harbour, Stalingrad and Dunkirk are all names that will forever be associated with the most brutal conflict the world has ever seen. 

But for all of these cataclysmic theatres of conflict, there were many more locations we simply don’t know about, where hundreds of thousands worked tirelessly for the greater good, on one side or the other. From the factory employees churning out bullets and tanks to radar operators and the dockworkers on the U.S east coast frantically filling ships destined for Europe.   

And this is a story of one such location. A place set in the calm undulating hills of middle England – a place called Bletchley Park. At first glance today Bletchley Park looks like many other stately homes dotted around the UK. Grand, well kept, with more than a splash of the Downton Abbey to it. But this was also the site of one of the extraordinary feats during World War II and one which undoubtedly helped tip the tide of war in the Allies’ favour. It was here that the previously thought ‘unbreakable’ Enigma machine finally met its match. 

Seven Enigma machines are shown, from left to right

The Enigma Machine   

Almost all communication sent back and forth during World War II was coded to some degree or another. After all, what good are secretive tactical manoeuvres if the enemy already knows what’s coming? 

Some nations were more adept at this than others, but almost everybody slipped up at some point. While commanders liked to imagine their tactics were closely guarded secrets, the reality was that through spies, enemy reconnaissance, misplaced maps and of course code-breaking, many missions were known in advance. 

But the Germans were pretty good at keeping their secrets close to their chest and pivotal to this was the Enigma machine. What looked like a glorified old fashioned typewriter, the Enigma Machine was the scourge of the allies for many years. Like a typewriter, it came with 26 keys corresponding to the letters of the alphabet, with a set of 26 lights (again with the letters of the alphabet) above. 

Also included was an electromechanical rotor mechanism located between the letters and the lights. This included three separate rotors (a fourth was later added) which could be rotated into a position that corresponded to letters beside them. So rotor 1 had 26 possibilities, as did rotor 2 and so on. Now, I could spend many hours going through the mechanical process of the Enigma machine but we have a lot to get through, so let me summarize.

The Germans changed the rotor settings daily, but if you had the correct rotor positions, you could type in encrypted messages that sounded completely gibberish to you and me, and the Enigma machine would translate it into a readable text. 

But alas, that was only half of it. On the front of the Enigma machine was the plugboard, which looked a bit like one of those old fashioned switchboards that telephone operators used to use. The plugboard contained small holes with the letters A-Z and a typical Enigma code would use ten different randomized pairs that needed to be connected via small wires, on top of the rotors that also needed to be in the correct position. The result, a difficult to comprehend 159 quintillion possible combinations.         

The Enigma machine was considered unbreakable by the Nazi – didn’t they say something similar about the Titanic? – so much so that even the most top-secret communications were often sent via the Enigma. But with odds like that, you can understand their confidence.  


Ok, to start the story we need to backtrack a bit because while the Enigma machine rose to fame during World War II, it was invented shortly after the First World War. It was quite rudimentary at that point but was commonly used across the German armed forces throughout the 1920s and 1930s. 

As we know, things started to go a little Aryian Nation in Germany in the 1930s and many of its neighbours began eyeing it suspiciously. One of these was Poland where they were able to build their own Enigma machines based on German cypher materials obtained by a French spy, Hans-Thilo Schmidt. With these machines, they were able to break some Nazi codes, but with war looming, the Germans added more rotors to their Enigams and the Poles simply couldn’t keep up. Just two months before the invasion of their country, the Poles gave a crash course to members of the British and French intelligence services in their enigma breaking techniques. 

Very few people know about the exchange of information that took place on 26th and 27th July 1939, in Pyry near Warsaw, but it was a meeting that would have a profound impact on World War II. 

War and the Unbreakable Enigma Machine

Not a whole lot went well for the Allies in the early stages of the war. Scores of German military success saw them roar across Europe and by mid-1940, most of the continent lay under the control of the Nazis. But at Bletchley Park, which housed the Government Code and Cypher School (GC&CS), there were some early successes. 

Alan Turing, a brilliant mathematician and computer scientist had arrived at Bletchley Park in 1939 – the very day on which Britain had declared war on Nazi Germany. He had been working part-time for the GC&CS since 1938, but with the outbreak of war, his genius was called upon full-time. He may not have always been the easiest person to work with, but Turing was one man who made an enormous impact on World War II. 

The First Bombes

Much of the codebreaking magic that happened at Bletchley Park began at least in Hut 8, little more than a small shack where the secrets of Nazi Germany were slowly uncovered. Just weeks after arriving at Bletchley Park, Turing deduced that the best, and perhaps only, way to beat the enigma machine was to build another machine that could match it. 

The idea to build an electromechanical machine called the bombe, based on the Polish bomba kryptologiczna, which had been built before the war, raised some eyebrows. While machines were certainly being used, they were still in their infancy and much of the hard codebreaking work was still done by the good old human brain. But Turing correctly reasoned that to break the thousands of German messages quickly and efficiently, British intelligence would have to go automatic. 

By March 1940, the first British Bombe, ambitiously named ‘Victory’, was up and running at Bletchley Park. This large machine didn’t actually decode the messages themselves but rather shifted through the countless potential possibilities for the adjustable rotors and plugboard to find the appropriate ‘key’ for that day. Once the key was found, in theory, all messages received on that day could then be decoded. The problem was that different Enigma codes were used across the German armed forces.  

These were big machines, measuring 2.1 metres (7 feet ) wide, 1.98 metres (6 feet 6 inches) tall, 0.61 metres (2 feet) deep and weighed about a ton. Each had space on the front for 108 small drums, arranged in three groups of 12 triplets. Each triplet corresponded to the three rotors of an Enigma scrambler and essentially these drums would mimic a human testing every possible option but in a fraction of the time. On the first bombes, the drums rotated at a speed of 50.4 rpm, while the later versions tore around at 120 rpm and were able to test all 17,576 possible positions for one rotor order in just 20 minutes.

The second Bombe, named Agnus dei, later shortened to “Agnes”, or “Aggie” was installed in August 1940. In just 1940 alone, the two Bombes successfully broke the German codes 178 times, while bombe outstations were established, at Adstock, Gayhurst and Wavendon, all close to Bletchley Park, in case it was hit during a bombing raid.   

Lucky Breaks

While things were progressing nicely at Bletchley, it was still a painstakingly slow process. What would really speed things up was if the allies could capture Enigma keys from their German foes, without the Germans realising and changing the keys. Sounds far-fetched, but it happened several times.

The first came on 26th April 1940, when a German patrol boat disguised as a Dutch trawler was captured by HMS Griffin off the Norwegian coast. Perhaps taken by surprise, the German crew onboard failed to destroy their crypto information and suddenly the British were in possession of some of the Enigma keys from 23rd to 26th April.

These keys were rushed back to Bletchley Park where they were utilized along with the bombe machines. Over the next two months, Turing and those working with him were able to break six days of naval traffic between 22nd and 27th April 1940. Of course, at this point, the information was well out of date, but this represented the first time Bletchley Park had broken the Kriegsmarine (German Navy) messages. And it’s probably worth pointing out here that the German Navy was by far the biggest threat to allies as it continued to decimate the merchant fleet moving between the U.S and Britain.   

The second capture of Enigma material came on 9th May 1941 in the icy waters off Greenland and has come to be known as Operation Primrose. The U-boat, U110, had travelled northwest from France to intercept convoy OB 318, moving from the U.S to Britain. The German submarine successfully sank the Esmond and Bengore Head, but it faced a fierce barrage from the convoy’s escort ships and the U-boat was eventually forced to the surface. 

The ocean surface when surrounded by enemy ships with all guns pointed at you, is just about as bad as it gets for a submarine and that was exactly what U110 faced as it broke the surface. As the crew gathered on the deck they came under from the British boats who believed the deck gun was about to be used. Once it became clear the German sailors were surrendering the shooting stopped and those on the deck began swimming towards the waiting boats. 

One of those in the water was Captain Fritz-Julius Lemp. Now, we have to speculate a little here but it seems as if Lemp had been sure that the U-110 was about to sink. But as he paddled away from the stricken U-boat, he apparently realised that the submarine was very much still floating and no doubt his second thought was of the top-secret crypto information still on board. Lemp is said to have turned around and headed back to the U-boat, but he never made it and was never seen again. 

The British boarded the U-110 and stripped it of everything worthwhile, including the submarine’s Kurzsignale codebook and Enigma machine. The allies couldn’t believe their luck and once again the information was again rushed to the small shack at Bletchley Park.  

The Expanding Bombes  

As in poker, sometimes you just need to go all-in, and that was exactly what Turing and his codebreakers did in 1941 with a carefully worded letter to the right man. By the summer of 1941, there were 4 to 6 bombes at Bletchley Park, with a total of 24 to 30 in the local area, but this was still not enough. The torrent of information coming in was enormous, and the allocation of funding and personnel was seen as inadequate by the codebreakers in order to keep up. 

Military rules are fairly explicit about the chain of command, you never go above your direct superior. But in October 1941, the codebreakers did, and not only that, they went to the very top. In their letter to Prime Minister Winston Churchill, the codebreakers bluntly stated that their work was being held and sometimes not being done at all because of lack of resources. It was an audacious move, but one that paid off. Churchill had visited Bletchley Park shortly before and was already convinced by the team’s excellent work. From then on, budget issues and lack of personnel were things of the past.       

Just to give you a quick idea of how quickly they were built, in December 1943 there were 87 bombes, a year later at the end of 1944, 152, and by the end of the war, the number had peaked at 155. These bombes were operated by a legion of women from the Women’s Royal Naval Service, known as Wrens.  

But while this might give the impression of smooth sailing, it really wasn’t. The huge increase in bombe numbers was partly because, in 1942, the German High Command ordered that a fourth rotor be added to all Enigma machines. This threw a real spanner in the works and led to the longest information blackout since those at Bletchley park had begun breaking the enigma codes.

The role of the bombe machines proved invaluable to breaking the Enigma codes, but it was human input that began to fill in the gaps. While an Enigma message may have appeared to be nothing but gibberish, there were patterns if you looked hard enough. 

The codebreakers knew that the Germans sent weather reports every day which meant that the word weather was included frequently. Most German messages also ended with the phrase ‘Heil Hitler’ and once the British discovered that all numbers were being spelt out rather than simply the number, they were able to go back and look at past messages and begin seeing similarities. This was by no means enough to read a whole message, but little by little their understanding of Enigma grew. 

Another quite obvious fact when you think about it, but was missed for a while, was that no letter was ever encrypted as itself. An ‘A’ couldn’t be encrypted as ‘A’ for example, which when combined across a whole message began to lower potential possibilities. 

Impact on the War

The work done at Bletchley Park, and the countless satellite stations surrounding it, had a staggering impact on the war. The only argument it would seem was just how much of an impact. Even as early as 1943, the codebreakers were cracking 84,000 enigma messages each month – equal to two each minute. The information gathered by the code-breakers was referred to as ‘Ultra’ intelligence and the powers that be guarded the information carefully. Even top commanders were often kept in the dark regarding the source of selected information.  

The quite obvious problem was, how do you exploit the information without revealing that you’ve cracked the code. Time and time again, German suspicions led to a sudden change in keys or as I mentioned, the installation of a fourth rotor. There were several instances where the allies had prior knowledge of events or attacks and chose not to pass on the information to troops on the ground or at sea. The painful reality was that codebreakers often knew that soldiers or merchant sailors were about to be attacked, but for the greater good, no action was taken. 

But that’s not to say it wasn’t carefully utilized. Information regarding Ermin Rommel’s intentions in North Africa was passed on to commanders on the ground and proved invaluable in finally defeating the most feared commander in the German Wehrmacht. The formidable German vessel, Bismarck, was finally sunk using information from broken Enigma messages, while the allies were also able to use them to assess German defensive capabilities before D-Day.  

Enigma was also used to plot U-boat patterns in the Atlantic Ocean, which unquestionably saved many ships and countless lives in the process. By 1945, almost all Enigma codes being sent across the three German military arms were being decoded within a day or two. The allies were able to read direct communication between German commanders as the allies swept across the continent at breakneck speed.

The question of whether the work by the enigma codebreakers shortened the war is one that historians come back to again and again. Some say a year, others say two – when you put it like that, what happened in the leafy tranquillity of Buckinghamshire, just north of London, may well have been some of the most important work across the entire war. 

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The Human Touch      

It’s easy to focus on the bombes and their relentless search for the Enigma codes, but this is a story that has quite extraordinary human actions throughout. Inexplicably, the role of the Polish codebreakers is often overlooked. Simply put, much of this may never have even happened had the Poles not had the foresight to construct their own Enigma machines and pass on everything they knew to allies just months before Poland was overrun.  

The work of Marian Rejewski, Henryk Zygalski and Jerzy Różycki, which began in 1932, a year before Hitler even became Chancellor, laid the foundations for everything that was to come. 

While there were thousands of unsung heroes working to decipher Enigma, we often come back to Gordon Welchman and of course Alan Turing, two men with vastly different personalities and temperaments, and who experienced two very different post-war experiences. Welchman, who had been instrumental in the further developments of the bombes, eventually moved to the U.S and became a professor at MIT, before passing away at the age of 79. 

The story of Alan Turing is altogether darker. In 1952, he was charged with gross indecency relating to a homosexual act, which was still a criminal offence in the UK at the time. He pleaded guilty and escaped a jail term on the condition he undergo chemical castration to reduce his libido and no doubt “cure” his homosexuality. Two years later, his housekeeper discovered his body amid his messy apartment. He had committed suicide by taking cyanide, at the age of just 41 years old. 

It wasn’t until 2012 that the British government officially pardoned Alan Turing, nearly 60 years after his death. For a long time his full involvement with the Enigma code-breaking wasn’t known (the operation wasn’t declassified until the 1970s) but today Turing is rightly revered as one of the most extraordinary British mathematicians and computer scientists. One man can’t win a war, but one man can make a truly remarkable contribution. 

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