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World War Two: The Enigma Code Breakers Part 1

Updated on February 2, 2014

Throughout World War Two the Nazis believed that their Enigma coding machine was unbreakable, but the British had uncovered it's secrets. This ultimately shortened the war by an estimated 3 years and by the 8th May 1945, when the Allied leaders were celebrating victory in Europe, the jubilant public were completely unaware of the vital role the code breakers had played in the downfall of Nazi Germany.

Bletchley Park
Bletchley Park

Bletchley Park

The private war against Enigma had been played out at a secret country house named Bletchley Park in the heart of the English countryside. It was to be the setting for arguably the most successful technical accomplishments of the entire second world war.

The decyphering of Enigma played a decisive role in the defeat of Erwin Rommel's Afrika Korps in North Africa. In the battle for the Atlantic, the longest campaign of the war, the achievements of the Bletchley Park codebreakers meant the difference between ultimate victory or defeat and it also aided in the liberation of northwestern Europe following the D-Day landings.

Bletchley Park was the home of World War Two's greatest secret and part of the clandestine history of the conflict which was not revealed until nearly 30 years after the end of the war.

When the Germans later discovered that their secret messages and orders had been continually intercepted and decyphered by the Allies, they were dumbfounded. Nowhere was the codebreakers achievenents more appreciated than in the constant struggle against the German U-Boats in the battle for control of the Atlantic.

The U-Boats had in their power the ability to starve the British people to defeat, as Britain's Prime Minister Winston Churchill later wrote " The only thing that ever frightened me during the war was the U-Boat peril". Without the breaking of Enigma, the war in the Atlantic and the war as a whole, may well have been lost.

Commander Wilfred Dunderdale
Commander Wilfred Dunderdale
Colonel Stewart Menzies
Colonel Stewart Menzies
The Enigma Machine
The Enigma Machine

The Enigma Machine

In August 1939, preparations were being made for an inevitable war with Germany and on the 16th August as thousands of young men answered the call to arms, two officers arrived at London's victoria Station.

The first of these men was Commander Wilfred Dunderdale of Britsh Intelligence in Paris. Dunderdale was acting as a minder for his travelling companion Captain Gustave Bertrand, the head of the code and cypher departments of French Intelligence.

He had carried with him an ordinary looking case which he handed to a man in a dinner jacket which exhibited the red ribbon of the Legion D'honneur. This man was Colonel Stewart Menzies the Deputy Chief of the British Secret Intelligence Service or S.I.S.

The unremarkable case contained a replica of Germany's top secret Cypher Machine E, better known as the Enigma machine. The machine had been built in the 1920s as a tool for businessmen to keep commercial exchanges secret.

In 1923 the German Navy began to use the machine and by the 1930s it had become the standard equipment for all Germany's Armed Services and Intelligence departments.

Eventually over 100,000 Enigma machines were made, it resembled a typewriter, but it was powereed by a battery and used no paper. It's encoded messages were transmitted in Morse Code to then be decoded by a second Enigma machine by the reciever.

At the core of the machine were 3 important components, the keyboard, a plug board and 3 rotors each containing the 26 letters of the alphabet.

When the operator pressed a key it sent an electric pulse through the machine. It passed through the plug-board where it was then re-routed to the first of the 3 rotors containing the alphabet.

It was on these rotors that the operator made the settings for the Enigma machine and at the height of the war, these were changed as frequently as every 8 hours.

Small windows on the machine displayed the letters on the rotors indicated by their numerical order in the alphabet. Each time the operator depressed a key, the right hand motor moved forward by one letter, then the centre rotor and finally the left.

The pulse passed from right to left through the wires in each of the 3 rotors, it was then bounced back by a reflector from left to right. On it's return journey, the pulse re-entered the intricate plug-board where it was re-routed for a second time.

It's final destination was a light-board over the keys which lit up with the transported letter. The letter that it lit depended on the settings of the machine and this could be done at the extraordinary number of 150 million, million, million ways.

The encoded message was then sent by Morse to be decoded by the receiving machine which had been set to the daily key.

Given the almost infinite number of settings and the frequency in which these were changed the Germans were of course convinced that Enigma was secure, but they were to be fatally mistaken.

General Hans Von Seeckt
General Hans Von Seeckt

The Fall & Rise of Germany

After Germany's defeat in the First World War, the Versaille Treaty aimed to insure that German military power would never again threaten peace. The west bank of the Rhine and the coal fields of the Saar Valley were occupied by Allied troops.

The German Army was reduced to 100,000 men and denied heavy artillery or air support, however, rearmament was secretly underway by the 1920s under the guidance of General Von Seeckt.

The Gernan Navy then began to developed the Enigma machine for secret military purposes. Enigma machines remained on sale until the end of the 1920s for commercial use. The pace of German rearmament was then increased with the coming to power of Adolf Hitler in 1933.

The first mobile tactics taking shape in the German Army would depend on the rapid and seemingly secure communications offered by the Enigma machine.

France and Poland had become increasingly concerned by the speed and the scale of the German rearmament and the Poles in particular moved swiftly to tackle the baffling new German cyphers and they assembled a codebreaking team known only as BS4.

Aware of the original commercial Enigma machine, the German military continually refined their encyphering procedures.

Commander Denniston
Commander Denniston


By 1938 the machine's operators were being directed to set their machines at random rather than from instructions in their manuals, extra wheels were also added to the machines.

The Polish codebreakers were now on the backfoot and appealed to the French for help, in January 1939 Gustave Bertrand arranged a meeting in Paris between French, Polish and British codebreakers.

In July they travelled to Warsaw to meet at a bunker compound outside of the Polish capital, the nerve centre of the Polish assault on the Enigma code. In the British team was Commander Alistair Denniston, Head of the British codebreaking team at Bletchley Park.

The meeting with the Poles hadn't come a moment too soon as Hitler was now making his move and on the 1st September 1939, his ofrces invaded Poland. The Polish campaign lasted barely a month and Warsaw was the first of Europe's great cities to come under aerial bombardment.

By the time the victorious German Army marched through the streets of Warsaw, the Polish codebreakers had destroyed their work and fled. Some of them had been captured and subjected to torture, but none of them revealed that they had cracked the Enigma code.

The French organisation provided the surviving Polish codebreakers with temporary refuge, but after France itself fell in the summer of 1940, the British were left to fight the battle against Enigma single-handed.

Alfred Dilwyn Knox
Alfred Dilwyn Knox
Gordon Welchman
Gordon Welchman
Alan Turing
Alan Turing

The Bletchley Network

Their strongest weapon by this stage was the German ignorance of how severely the Enigma code had been comprimised. Bletchley had in 1938 became the focal point of the government's decyphering school, later renamed the Government Communications Headquarters or GCHQ.

It is now merely a shrine to the men and women who worked there and the British wartime leader who realised it's importance, Prime Minister Winston Churchill. Bletchley had begun it's task in the late summer of 1938, when the radio room (codenamed station X) was installed inside one of the building's towers.

The radio's aerial was slung between the rooftop and a cedar tree in the grounds which still stands today. From these modest beginnings the school spread over the grounds of the house in many huts and concrete encampments employing around 10,000 personnel working 24 hours a day over 3 shifts.

Bletchley had become a self-contained intelligence suburb whose workers were bussed in from surrounding towns and villages where they were billeted.

Commander Denniston's second in command and codebreaking chief was a civilian Alfred Dilwyn Knox and a third key member of the team Gordon Welchman established the working methods at Bletchley Park.

To overcome Enigma, Denniston employed brilliant mathemiticians and chess masters, among these mathemiticians was Alan Turing who had in 1936 devised a theoretical universal computing machine. Turing designed new and sophisticated versions of the Pole's key scanning bombs, known as Bronze Goddesses and they went to work on the Enigma keys.

The bomb designed by Turing was an electro-mechanical machine that was matched to the electrical wiring of the Enigma machine to solve the successive changes to the key. To the bomb was added Turing's outstanding brainpower, in 1942 the German U-Boat Service added a fourth rotor to the Enigma machines carried by it's submarines. Turing locked himself away in the bedroom of a small house in Bletchley's stable block and here he fought a lone battle against the complexities of the fourth rotor.

The work at Bletchley was based on a hut system devised by Welchman, the huts worked in pairs, one on the decryption of Enigma signals, the other on translation and analysis.

In Hut 3, some of the earliest decryptions of the war were handled, as well as the sorting and prioritising of the intercepted signals. At the start of the war Hut 6 was used for decrypting German Army and Air Force codes. Huts 4 and 8 dealt with German naval codes.

As the importance of the huts grew, so di their staffing needs and by the end of the war, Hut 3 had become no longer just a single wooden structure, but a whole range of locations and buildings all over Bletchley Park.

By the end of the war, Bletchley had read 500,000 encoded messages by the German Navy alone. Also, in Hut 6, two dozen Enigma cyphers were being read, including those used by the Army, Air Force, S.S, Police and the German railway system, many of thse were being read in "real time"

Utilising the information

The vast horde of information that had been accumulated by Blethchley Park, from strategic decisions made by Hitler himself to the movements of individual officers from one unit to another, was filed away in the massive card index system that was housed in Bletchley's C Block.

The work of the indexers, most of whom were young women, created a huge store of knowledge which was constantly being screened for information large or small.

After passing through the hands of the Y Service and the codebreakers, the Enigma decrypts arrived at what was known as the "Hut Watch". These were a team of fluent German speakers who sat at a table translating them into English and filing them according to priority.

They were then passed on to teams of military advisers for evaluation as the Hut Watch, like most at Bletchley, worked around the clock. The more widely Enigma was being used, the more likely it became that lazy operators were failing to observe the strict rules for encyphering messages. Careless encyphering opened the door for Bletchley's codebreakers.

The Enigma operators in the Luftwaffe proved to be the most careless of all, one particular signaller used his girlfriend's initials as his 3 letter key, little realising the damage he was doing to his own service and to the entire German Air Force.

As the war continued, the sheer mass of detailed information gathered at Bletchley of the daily life of the Luftwaffe, matched that of the German High Command itself.

The airwaves were neutral, carrying messages to obscure German officers and Hitler himself, to his commanders in the field. The knowledge they provided, not only of the German's precise strength, but also where they intended to carry out their operations, brought about a new dimension to the war.

The codebreakers at Bletchley had virtually given the Allied leaders a seat at Hitler's own war table.

Churchill in the Cabinet War Rooms
Churchill in the Cabinet War Rooms
The Lockhead Electra
The Lockhead Electra


The information Bletchley gathered was codenamed ULTRA, Churchill had originally called it his "Ultra Secret". From the outset however, British Intelligence was faced with the problem of how best to distribute the Enigma information to it's own commanders in the field without the German's discovering that their signals were being read.

Any leak in security surrounding the ULTRA secret could prove fatal and the task was given to the Head of the Air Department of the Secret Intelligence Service or S.I.S. Wing Commander Fred Winterbottom, who had learnt fluent German after being taken prisoner in the First World War.

In 1929, Winterbottom had become Head of the Air Intelligence Branch and quickly established a network of agents in Germany. After Hitler rose to power in 1933, Winterbottom travelled all over the country, befriending prominent Nazis and claiming to admire the Fuhrer.

When in the late 1930s his cover was blown, Winterbottom launched an aerial spying programme over Germany using a Lockhead Electra that carried specially designed spying cameras. At Bletchley park, he became Churchill's personal representative and set up a network of Special Liaison units or S.L.U's that were staffed by non-commissioned officers who were attached to headquarters in the field and these were trained to pass on the relevant ULTRA information to the senior commanders.

Prime Minister Churchill received a regular flow of ULTRA decrypts directly from Bletchley Park. and he revelled at being at the heart of the ULTRA secret. Aware of the huge array of information it produced with the minimum of fuss, he affectionately described Bletchley as his "Golden goose that never cackles".

Commanders in the field received the ULTRA information only when it concerned them, directly from their S.L.U. personnel who then immediately destroyed the signal. Churchill insisted that no operational use could be made of ULTRA information without commanders like Field Marshall Montgomery developing a cover plan that would convince the Germnans that the intelligence came from a source other than Enigma.

Naval ULTRA was handled differently, in contrast to the War Office or Air Ministry, the Admiralty was a department of state which also conducted operations, issuing orders to it's commanders at sea hour by hour. The results of the decryption and intelligence work in Bletchley's Huts 4 and 8 went straight to the Admiralty in London and nowhere else.

Japanese attack on Pearl Harbor, December 1941
Japanese attack on Pearl Harbor, December 1941
Captain William Bundy
Captain William Bundy

American intervention & the Soviet spy

The Japanese attack on Pearl Harbor in December 1941, brought the United States into the war and from then on the British shared the secret ULTRA information with their American allies.

Teams of American codebreakers began to arrive at Bletchley Park to work alongside their British counterparts. Leading the Americans in Hut 6 was a Captain William Bundy, but Churchill's Soviet ally Joseph Stalin was not to share in the ULTRA secret.

Stalin was only sent digests of ULTRA information by a number of routes which did not reveal their source. Too often however, the heavily laundered information reached the Russians too late to have any benefit on the Soviet Union's desperate struggle on the Eastern Front.

As the war on the Eastern Front continued, the Russians made no attempt to probe Allied leaders or diplomats on the source of the information they were receiving. The reason was that the Russians knew a lot about ULTRA already, for they had a spy in place at Bletchley Park.

He was John Cairncross, an army staff officer who had been recruited by Soviet Intelligence while he was an under-graduate at Cambridge University. He worked in Hut 6 where the Luftwaffe Enigma traffic was decrypted. He was able to gather decrypts which merely lay on the floor of Hut 6 at the end of the working day and hide them on his person before transferring them to a bag.

On trips to London, Cairncross handed over the bag to his Russian controller who sifted through the information obtained by Cairncross concerning the German air movements that preceeded Hitler's offensive at Kursk in the Ukraine on the 5th July 1943.

Acting on Cairncross's information, the Soviet Air Force launched a pre-emptive strike aimed at destroying the Luftwaffe on the ground. But as the German armoured prepared to advance, it was the Russian aircraft that suffered a severe onslaught from the Luftwaffe who had scrambled their planes just minutes before.

It was a crushing blow and it enabled the Luftwaffe's 8th Air Corps to operate at will over the battlefield for the next 5 hours of the battle. The pre-emptive Russian strike had almost cost the Red Army the battle before it had even begun.

However, the German Panxers were eventually ground to a halt and Stalin awarded Cairncross a medal, despite this, his part in the German defeat remained open to question. Stalin knew all too well about ULTRA , but Hitler never did, even though the Germans did have several clues in their possession, though they never realised the conclusion that Enigma had been fatally penetrated.

A B-17 bomber crashing during WW2
A B-17 bomber crashing during WW2

Keeping the secret, secret

In September 1942, one of the Royal Navy's motor gunboats was captured along with it's charts and documents detailing German convoy movements and minefield channels. The information could only have come from Enigma signals, but incredibly the suspicion of German Intelligence was never aroused.

A situation that was potentially a lot more hazardous was when an American Army Air Force officer based in England who knew about the Enigma secret fell into German hands. The officer was Brigadier General Arthur W.Vannerman, the Air Intelligence officer at the headquarters of the U.S. 8th Air Force, commanded by the famed General James Doolittle.

Against all good sense, Vannerman was allowed to fly a combat mission over France and on the 27th June 1944, Vannerman's B-17 was shot down. He survived, but was imprisoned at Stalag Luft 3, the scene of the Great Escape.

He spent the erst of the war terrified that he may inadvertently reveal the ULTRA secret, for he knew only too well that he talked in his sleep. However, the secret stayed safe with vannerman although on his return to the United States at the end of the war, he had to suffer the indignity of being demoted down to Colonel.

The Lorenz Enigma machine
The Lorenz Enigma machine
The Colossus computer
The Colossus computer

The New Enigma Machine

Throughout the war the Germans constantly refined their encoding procedures, the Lorenz machine used by the German Army at command level, had no less than 12 wheels and worked as a decyphering system attached to a teleprinter.

The encypherment of Lorenz was extremely complicated, each of the 12 wheels was set to a pattern determined by sheets for a given day and network. There were 501 small metal tags that had to be correctly set.

The codebreakers task was to find the wheel patterns for a particular key and then the wheel start positions for a given message. The number of possible combinations was an astounding 10 million, million, million.

To crack the code a British Post Office team built the world's first electronic programmable computer, codenamed Colossus. The Mark2 Colossus was online by the 1st June 1944, 5 days before the allied invasion of Europe.

The intercepted messages were fed into the computer on the 5 Hole teleprinter code used by the Lorenz and similair machines. The tape was read at very high speed, 5,000 characters a second and the Colossus circuits were synchronised to the sprocket holes in the tape.

The holes in the tape were read using photocells, Colossus then internally generated the key streams to be compared with the intercepted encyphered messages. The results of the run were then printed on an electric typewriter.

Once Colossus operators and the codebreakers established the wheel patterns, a tiny machine was set up that would decypher the intercepted message into German text.

The Mark2 Colossus ran on 2,500 valves, these days a modern microchip smaller than a thumbnail can handle the tasks performed by the groundbreaking Colossus. The prize at stake was priceless, no less than the ability to read the messages passing between Adolf Hitler and his generals.


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    • alancaster149 profile image

      Alan R Lancaster 

      2 years ago from Forest Gate, London E7, U K (ex-pat Yorkshire)

      Hello again Dave, exhaustive research you've undertaken here. Gives another aspect to the interception of code books and machine the Navy got hold of from a sinking U-boat in the Med halfway through the war. That's the avenue I used in my page. There was another 'way in', in that one of the Luftwaffe signallers used his girlfriend's nickname in messages. There was another story, that all the German services personnel sent congratulatory messages to Hitler on his birthday.

      In another case, Ian Fleming was aboard a destroyer off Dieppe in August, 1942, waiting for commandos to bring him a set of codes and a machine from a hotel used by the Kriegsmarine as HQ near the harbour. The 'snatch' didn't come off and Commander Fleming had to go back empty-handed. Luckily the U-boat was intercepted a short time later.

    • profile image


      5 years ago

      See my own article

      which gives the other scientists the credit they deserve.

    • profile image


      6 years ago

      This article was so insightful! I used it to aide me with my ninth grade global studies project. Thanks so much!

    • Dave Harris profile imageAUTHOR

      Dave Harris 

      6 years ago from Cardiff, UK

      Thankyou Alex, glad it was of interest to you.

    • profile image


      6 years ago

      Very useful :) and so many great insights!

    • Dave Harris profile imageAUTHOR

      Dave Harris 

      7 years ago from Cardiff, UK

      Hi daryl2007, thanks for your comments, glad you are enjoying my hubs!

    • daryl2007 profile image


      7 years ago

      Wow I always love to know more about these guys...code breakers!!! Great work! I love the article!!! great message keep it up!!

    • Dave Harris profile imageAUTHOR

      Dave Harris 

      7 years ago from Cardiff, UK

      Thankyou The_Ali, hope you enjoyed it!

    • The_Ali profile image


      7 years ago from USA

      very useful thanks.


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