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Look inside Bletchley Park and get up close with an original Enigma machine

Our behind-the-scenes snaps show you how the fiendish Nazi Enigma machine encoded its messages, and the unassuming offices where the code was cracked.

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Luke Westaway
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1 of 23 Andrew Hoyle/CNET

CNET's 360-degree tour of Bletchley Park, now live on YouTube, takes you inside Britain's wartime codebreaking headquarters. Be sure to check it out, then click through our photos from behind the scenes at Bletchley Park, where we got up close and personal with an original Enigma machine.

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2 of 23 Andrew Hoyle/CNET

Dominating the view of Bletchley Park is the mansion. Bletchley, in Buckinghamshire, was ideally situated as a codebreaking site since it was accessible from London as well as university towns Oxford and Cambridge, from which many codebreakers were recruited.

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3 of 23 Andrew Hoyle/CNET

This is the office of Alastair Denniston. Denniston was involved in codebreaking throughout World War I, and was instrumental in establishing Bletchley Park as Britain's codebreaking nerve centre.

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4 of 23 Andrew Hoyle/CNET

This bust of prime minister Winston Churchill looks out over the main hall in the mansion.

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5 of 23 Andrew Hoyle/CNET

Away from the mansion's luxurious decor, codebreakers worked in cramped prefabricated huts, at desks like this one.

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6 of 23 Andrew Hoyle/CNET

Rooms at Bletchley Park are decked out in period style to give visitors an idea of what daily life there would have been like.

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7 of 23 Andrew Hoyle/CNET

Cryptographers at Bletchley managed to crack German communications without the aid of computers -- though their work would push computer science forward.

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8 of 23 Andrew Hoyle/CNET

This is the office of Alan Turing, in Bletchley Park's Hut 8.

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9 of 23 Andrew Hoyle/CNET

Alan Turing is perhaps history's best-known code breaker. This note left at the typewriter on his desk adds a little colour to the visitors' experience.

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10 of 23 Andrew Hoyle/CNET

Codebreakers needed a good grasp of German, as well as the phrases that the German military would be using.

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11 of 23 Andrew Hoyle/CNET

Posters like this were designed to help the war effort.

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12 of 23 Andrew Hoyle/CNET

Much of the Bletchley codebreakers' time was consumed by this -- a German military Enigma machine. Enemy forces used these machines to encode their communications, and the encryption was devilishly hard to crack.

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13 of 23 Andrew Hoyle/CNET

Enigma had one fatal design flaw, however. A letter could never be encoded as itself. So if you had an "a", you knew that letter wasn't really "a". Bletchley codebreakers also relied on "cribs", which were essentially best guesses at what a message could be about, and "pinches", where Enigma codebooks were stolen from the German military in the field.

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14 of 23 Andrew Hoyle/CNET

Encoding a message begins here. Typing a letter on the Enigma machine illuminates another letter.

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15 of 23 Andrew Hoyle/CNET

A close-up on the Enigma keyboard.

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16 of 23 Andrew Hoyle/CNET

Which letter is illuminated depends firstly on the arrangement of these rotors -- each of which has a possible 26 settings.

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17 of 23 Andrew Hoyle/CNET

Here's an individual Enigma rotor. The Enigma machine was used commercially as early as the 1920s -- but the evolving military variants added increasing levels of complexity, to make codes tougher to crack.

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18 of 23 Andrew Hoyle/CNET

Making things harder is the plug board, which swapped letters with other letters of the user's choice. In total, an Enigma machine offered over 150 million million million possible settings combinations.

To read an Enigma message, all you needed to do was replicate the rotor positions and plug board settings on your own machine, and the code would be swapped back into readable text. But without knowledge of those settings, turning Enigma code into readable text was next to impossible.

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19 of 23 Andrew Hoyle/CNET

Helping to crunch the numbers of possible Enigma settings combinations was the Bombe machine, a cumbersome, room-filling device pioneered by Alan Turing. Each wheel corresponded to an Enigma rotor position, and this electromechanical monster would rattle through possible settings combinations, hunting for configurations that made sense.

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20 of 23 Andrew Hoyle/CNET

The replica Bombe that sits on Bletchley grounds today took more than a decade to build.

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21 of 23 Andrew Hoyle/CNET

A view of the back of the replica Bombe.

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22 of 23 Andrew Hoyle/CNET

Another pioneering codebreaker was Gordon Welchman, who added the "Diagonal board" refinement to the Bombe machine.

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23 of 23 Andrew Hoyle/CNET

Historians credit the code-cracking efforts at Bletchley with shortening the war by several years. Don't forget to check out our immersive 360-degree tour.

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