Code-breakers: Secret War

It's 1940 and the Second World War is raging throughout London. You travel 50 miles north-west into the countryside and arrive at Bletchley Park, a beautiful manor house. You have no idea why you're there. You'll soon discover that the Nazis have created a ...

This story was created for the Google Expeditions project by Twig World, now available on Google Arts & Culture

ENIGMA - ELECTROMECHANICAL ENCRYPTION MACHINENational Museum of Science and Technology Leonardo Da Vinci

... secret communication system called the enigma code cipher that has made them almost unstoppable. You will soon become part of a beyond top-secret team that will try and crack the code, helping to win the war.

A Tranquil Place

Meet Christine. It’s her first day as a translator working at Bletchley Park in Buckinghamshire, UK. It’s your first day too, and you walk in together. Christine has travelled 50 miles north of London, which suffers nightly bombing raids because it’s 1941 and Britain is at war with the Nazis.

It’s comparatively tranquil here, as you walk towards the hut where you’ll work. You wonder why you had to sign the Official Secrets Act.

All is Not What it Seems

The buildings are reinforced to make them bombproof. You begin to think that this place is far more important than it first appeared. 

In the Trees

The buildings are hidden in the trees – probably to protect them from being spotted by enemy aircraft. 

Hut 6 at Bletchley Park, working on German army and air force Enigma messagesBletchley Park

The Bletchley Workforce

People are walking with purpose to the wooden huts around this concrete building, named Block A. About 10,000 people work here and 75% of them are women. Some are in uniform and some wear civilian clothes.

Walking Towards Hut 3

Hut 3 is the building you will work in. You speak fluent French and German and have an excellent academic history. Your new place of work looks dull on the outside, but inside is a hive of activity, with many people busy at their desks. 

Hut 3

You know that you will be translating messages from German into English. These messages seem to come from the German military and are full of military jargon. They are not always complete, and are sometimes almost meaningless. 

You will have to do your best to work out their meanings. 

Through the Door

No one has told you where the messages come from and you are encouraged not to ask questions. Even the training you received leaves you slightly unclear on what it is you are doing.

The Day Shift

Your shifts this week are 08.00–16.00, but Bletchley Park operates 24 hours a day, with shifts from 16.00–00.00 and 12.00–08.00. It doesn’t have the time to stop.

Working Your Shift

This is the inside of your hut, where you will do your translations. It is quiet and everyone is concentrating: people work with an intensity and sense of urgency because they know that the messages that they translate could save lives if they do it quickly enough. 

LIFE Photo Collection

Why Were These Messages So Important?

In 1941, merchant ships were bringing in food, fuel and raw materials to keep Britain in the war. Without them, the population would have starved and the country would have run out of weapons to fight with. 

People worked to intercept messages that indicated where the enemy was, so that they could protect these merchant ships.

LIFE Photo Collection


Merchant ships had no defence against German U-boats – submarines that could easily sink them with torpedoes. Each ship that was sunk meant Britain had less food and fuel to keep the country from starving and protect itself against Nazi Germany. 

A Signal of Consequence

You’ve translated a lot of messages today, but this one seems more important than the others. It appears to be the coordinates of a position in the Atlantic Ocean, sent from a German U-boat.

The Codebreakers

Before messages could be translated, the code – or cipher – had to be cracked. Alan Turing was one of those employed to crack codes, and ran Hut 8 along with Hugh Alexander.

Introducing Alan Turing by Twig World

Introducing Alan Turing

Alan Turing studied mathematics at Cambridge University and wrote his doctoral thesis at Princeton University. 

Portrait of Alan Mathison Turing (1951) by Walter StonemanThe Royal Society

In 1936 he wrote a paper called “On Computable Numbers”, where he described a “universal machine” that heavily influenced much of the development of computing as we know it today. He joined Bletchley Park on the first day of the war.


The messages that were intercepted are called ciphers, and could be cracked with a pen and paper. For example: the letter A becomes another letter in the alphabet using a rule that only you and the recipient of the message know. 

A good example is the Caesar cipher (or shift), which replaces each letter of the alphabet with the one a few letters before or after it.

Crack a Cipher by Twig World

Crack a Cipher

This word describes “what enables the wise sovereign and the good general to strike and conquer”. 

Crack Another Cipher by Twig World

Crack Another Cipher

Ciphers are where the letters in the true message are replaced with other letters, numbers or symbols using an agreed rule. Alan Turing and the other codebreakers were looking for patterns in the letters and numbers to get at the underlying rule. 

The Enigma Machine

This is the German Enigma machine. It was used to scramble plain text messages before they were transmitted over the radio. 

The Rotors

The rotors inside the Enigma machine were reset each day, which meant that if you didn’t crack the code in 24 hours, you had to start again. There were also plugs at the front of the machine that could be changed to further complicate the message. 

The operators all needed to know exactly what the settings for each day were.

Codebreakers at Work

This year – 1941 – the codebreakers will crack the Enigma machine ciphers, allowing the navy to locate the German U-boats. This will greatly reduce the number of British ships being sunk.

An Extra Rotor

The German Navy suspects that the Enigma machine ciphers are being cracked, and so redesign Enigma using 4 rotors rather than 3. Three men from the British HMS Petard will steal the new codebooks from a sinking U-boat, two of them dying in the process. 

The Bombe Machine

As the Enigma machines became more and more complicated, it became clear that human brainpower was not going to be enough to crack the ciphers. The system used strips of card to represent enigma rotors and codebreakers searched for relationships by hand, which took hours.  

Bombe machines appeared at Bletchley Park in 1940, as a more sophisticated alternative to this method.

The Bombe Machine

Alan Turing and Gordon Welchman took inspiration from Polish codebreakers, designing a machine that could work out possible combinations of letters by running many drums at once, like the rotors found in Enigma machines. 

108 Drums

Each machine had 108 drums, representing 36 possible settings on an Enigma machine. This meant that 17,576 possible combinations could be checked in 12 minutes. A drum would stop if it came across a rotor setting that looked like it might crack that day’s code.


Bombes could not work without some clues, and so the codebreakers intercepted messages that clearly started or ended the same way, or that used slang. Nazi operators that were not using the Enigma machines properly gave away certain clues, too.

Navy WAVE working on US Navy Cryptanalytic BombeSmithsonian's National Air and Space Museum

Incessant Noise

The Wrens that ran the Bombe machines did not have an easy time. The machines were noisy, they sprayed out oil and often had to be rewired with tweezers. 


At its peak, over 200,000 messages a day were processed at Bletchley Park by a close-knit, intelligent, hardworking team. We now know that the workers there probably shortened the Second World War by 2 years.


All messages were cross-referenced to check whether there was anything else held on file related to them. If the information was deemed important it was typed up into a report, as if from a fake spy. This step hid the fact that Bletchley had decoded it.


Top-level intelligence gained from deciphering Enigma codes and other messages was called Ultra. The management of Bletchley Park decided which messages to send to the government and the armed forces, and what kind of priority they should go under. 

Some messages were sent directly to Prime Minister Winston Churchill.

Attack on a Convoy Seen from the Air (1941) by Eurich, Richard Ernst (RA)Imperial War Museums

Battle of the Atlantic

Bletchley Park intelligence helped to locate and destroy German U-boats, making sure that imports of food and fuel continued flowing into Britain from the USA and other countries.

Troops of the US 7th Corps wading ashore on Utah Beach, 6 June 1944Imperial War Museums


In 1944, Bletchley Park broke the code of German High command and contributed to the success of the invasion of France (D-Day). Commanders could act confidently, as they knew what the enemy was thinking. 

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