60-second guide to Bletchley Park – the WW2 code-breaking centre that spawned the computer age and made the D-Day landings possible

Bletchley Park housed Britain’s key decryption centre during the Second World War, and is credited with shortening the conflict by at least two years...

The registration room in hut 6 at Bletchley Park, Buckinghamshire. (Getty)
The registration room in hut 6 at Bletchley Park, Buckinghamshire. (Getty)

Here, writing for History Extra, Sinclair McKay, the author of The Lost World Of Bletchley Park (Aurum Press) and The Secret Listeners, tells you everything you need to know about the famous decryption centre.

Q: What role did Bletchley Park play during the Second World War?

A: Bletchley Park was the Buckinghamshire house and estate that played host to Britain’s code-breaking triumphs – from the success in breaking the ‘insoluble’ Nazi Enigma codes to its incredible work on Japanese cryptology.

Its role was so secret – everyone who worked there signed the Official Secrets Act for life – that we only really started to learn about its achievements decades afterwards. And there is still much to emerge.

Q: When and how was the code-breaking centre established?

A: Before it was evacuated to Bletchley, the Government Code and Cypher School – as it was then known – operated from a building near Westminster. There had been a special code-breaking department since the First World War – then, it was referred to as ‘Room 40’.

In the interwar years, they analysed Soviet traffic, among other things. When it seemed obvious that war was coming once more, many of the expert cryptanalysts of Room 40 set up the new establishment at Bletchley in 1938. They recruited crucial new blood, including brilliant young mathematician Alan Turing, as well as lecturers and undergraduates from universities all over the country.

Q: How many code-breakers worked there? What did an average day consist of?

A: Numbers rose as the war went on; from a relatively small team in 1938 to something like 10,000 people – code-breakers, Wrens, WAAFs, posh debutantes working on the cross-indexing system etc.

Obviously, they didn’t live at the house. All these people, mainly young, were billeted around the town and nearby villages. Bletchley locals were disconcerted by some of the eccentric code-breakers, and they formed a theory that the secret establishment was in fact a special lunatic asylum.

There was no average day. Code-breaking went on round the clock, in a three-shift system, and in different huts – very often the work was done in plain wooden huts. There could either be months of agonising paralysis (as there was in the battle to crack the nightmarishly complex Naval Enigma) or nights of giddying triumph, as when 20-year-old Mavis Batey broke the code that led to British victory in the Battle of Cape Matapan.


Bletchley Park pictured in 1926. (Evening Standard/Getty Images)

Q: Roughly how many ciphers and codes were decrypted in total?

A: It is simply impossible to know – largely because Bletchley was so mind-bogglingly successful. They read messages from the German army, navy, air force, secret service… even messages from the desk of Hitler himself. Countless thousands upon thousands of communications.

They cracked Italian and Japanese cyphers, and the operation was spread across the whole wide world. In posts from Cairo to Murmansk, dedicated secret listeners for the Y Service intercepted all the secret coded radio messages – and relayed them back to England, and ultimately back to this incredible code-breaking factory.

The other miracle was the secrecy; the fact that the Germans never really guessed adds to this astonishing success.

Q: Is it true that the 'Ultra' intelligence produced at Bletchley Park shortened the war by two to four years?

A: President Eisenhower credited the work of ‘BP’, as it was called, with having shortened the war by two years. Think for a moment of how many lives those two years might represent; the countless people saved simply by the ending of the conflict.

Bletchley veteran and distinguished historian, Professor Sir Harry Hinsley, reckoned it was three years. Apart from anything else, without Bletchley’s absolutely crucial intelligence, the D-Day landings in 1944 might never have worked, and in the extra time it would have taken the Allies to get a foothold in Europe, who knows how many more victims the Nazis would have murdered? And what sort of new and terrible weapons the Nazis could have developed?

Bear in mind the other great element of the Bletchley story: thanks to a brilliant engineer called Tommy Flowers, the computer age was brought into being there. He developed a code-breaking machine – the Colossus – that was in effect a proto-computer. Engineers at Google and Apple recognise and pay tribute to the Park’s importance.  

Q: When was Bletchley Park decommissioned?

A: It was never decommissioned. Its work – and in some ways, its spirit and ethos – still goes on today. After the war, the work of the Park was packed up (all decrypts carefully destroyed) and first moved to Eastcote, in north-west London.

Some of the code-breakers stayed on. The need for their brilliance was still there – the war had simply turned Cold. After several years, new premises for the increasingly sophisticated technological operation were found, in the pleasant town of Cheltenham. They are still there now, and the organisation is better known as GCHQ.  

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