Bletchley Park: Britain's wartime intelligence factory

It is sometimes said that this operation shortened the Second World War by two or three years

The Buckinghamshire estate of Bletchley Park was the wartime home of the Government Code and Cipher School (GC & CS), the forerunner of today’s GCHQ. Formed after the First World War from the codebreaking facilities at the Admiralty and the War Office, by 1939 GC & CS was part of the Secret Intelligence Service (SIS or MI6), itself within the Foreign Office.

At the outbreak of war there were no more than 200 people working at Bletchley Park. Of these, only a handful were employed on Enigma, the cipher machine employed by various elements of the German war effort, such as the army and navy. Within those services, Enigma was employed by scores of different ‘user groups’, many of which were decoded at Bletchley from 1940 onwards.

It is therefore a misnomer to think of the breaking of Enigma as a single event – there were, in fact, multiple variants of the famous cipher machine, each changing their configuration daily. And Bletchley’s staff weren’t just faced with the task of decoding Enigma. Germany also used the even more complex Fish ciphers – for which the Colossus computing machine was built in 1944 – and there was also a range of Italian and Japanese ciphers to be dealt with.

Polish exploits

Bletchley Park was aided in its efforts to decipher Enigma by the prewar exploits of Polish codebreakers. This informed the work of Turing but also a team of colleagues including Dilly Knox, who had broken an Italian naval enigma cipher as early as 1937. It certainly wasn’t the case that Turing alone cracked Enigma, any more than there was a single Enigma to be cracked.

At the outbreak of war there were no more than 200 people working at Bletchley Park

And in any case, breaking an Enigma ‘user group’ was only the first stage. It enabled messages to be read, but what did the messages mean? The men and women of Bletchley Park could only find out by painstakingly synthesising and analysing thousands of decoded messages. This in turn meant that they had to develop a complex data management operation, mainly based on cross-referenced card indexes that were sometimes filed in shoeboxes. It also demanded that they created an intelligence assessment function, so that they could produce something useable to the Allies’ military commanders.

It was the task of handling huge volumes of Enigma decrypts so that solid military intelligence could be produced that made Gordon Welchman a key figure at Bletchley Park. A Cambridge mathematician, like his more famous colleague Alan Turing, Welchman devised the system that was to process thousands of messages each day – from interception through to decryption, translation and analysis.

• Read more about the evolution of British code-breaking

Welchman’s system met with some resistance. Interception was a problem, because the facilities to do this were run by the armed services, not Bletchley Park. Intelligence analysis was another, as this was a realm where the armed services were reluctant to relinquish control. But after many political battles, Welchman’s proposals largely prevailed, and Bletchley Park became much more independent from the various government ministries and armed services from which it had been created.

What this meant was that Bletchley Park became home to an enormous centralised ‘signals intelligence’ operation, which grew so rapidly that it soon expanded from the original mansion house to a complex of wooden huts and concrete blocks, many of which can still be seen today.

Many had no idea what they were working on – they merely knew that they had to complete their one little part of the process

What had been created was no less than an intelligence ‘factory’ which sucked in thousands of people working in conditions of complete secrecy. Everyone employed at Bletchley Park was told that they must never reveal anything of their work. Many had no idea what they were working on – they merely knew that they had to complete their one little part of the process.

And, as the secrecy was maintained until 1974, in some cases they died not knowing the value of their work. The secrecy gives rise to some delicious stories, such as the spouses who both worked at Bletchley Park yet only realised it when they met at a reunion.

Massive operation

What were all these people doing? So many things that it would be impossible to catalogue them all. Many operated and maintained the various machines used in codebreaking. Some were civilians: for example, those brought in from the British Machine Tabulating Company to work on the Hollerith data processing machines. Others were WRENs, the female branch of the navy, who operated the ‘bombes’, electromechanical devices that tested possible solutions to Enigmas. Still others, both civilian and military, were indexing clerks, running the massive operation to collate hundreds of thousands of decrypted messages.

• Read more about the women of Bletchley Park

There was also a complex infrastructure for housing, feeding and transporting the workforce, which typically worked on a three-shift basis throughout the day. There were even five people employed in the barber’s shop! An unsung hero at Bletchley Park was Alan Bradshaw, who throughout the war ran the entire administrative function that held this all together.

Bletchley Park moved from being simply a codebreaking operation to a more integrated signals intelligence entity, linking interception, cryptanalysis, translation, intelligence analysis and intelligence dissemination

For the most part, the more humdrum activities were performed by women. True, there were some female codebreakers – Mavis Batey and Joan Murray among the best known; Margaret Rock and Ruth Briggs, less so – and women could be found in highly skilled roles such as translation and intelligence assessment. Yet, more commonly, they performed routine, repetitive and often physically arduous jobs. And the prevalent modern perception of aristocratic ‘debutantes’ using their family connections to secure berths at Bletchley Park is largely misleading. In reality, Bletchley Park’s female employees hailed from a wide variety of backgrounds.

It would be wrong, then, to think of Bletchley Park as a genteel club where eccentric male geniuses performed complex mathematical calculations. Rebecca Ratcliff, who compared British and German codebreaking, shows how the German effort suffered from being fragmented, whereas Bletchley Park brought much of the capacity together. The amalgamation of codebreaking with intelligence analysis was what made the work of Turing and his fellow cryptanalysts useful. And it was the Welchman factory that allowed Bletchley Park to churn out this intelligence in volume.

Of course that factory would not have existed had it not been for the codebreakers. But without the factory it is inconceivable that the codebreakers would have had the significant impact that they did on the conduct of the war.

Christopher Grey is professor of organisational behaviour at Warwick University. He held a Leverhulme major research fellowship to study the organisation of Bletchley Park.

This article was first published in the April 2012 issue of BBC History Magazine