3.1 Bletchley Park

Bletchley Park, the home of the Government Code and Cypher School (GC and CS), was formed in 1920 under the control of Naval Intelligence. The interception of enemy radio communications by the British was key during the First World War and even more important in the second.

GC and CS, moved to the Bletchley Park Estate in 1938. The estate was conveniently located on the main line from London and equidistant from Oxford and Cambridge universities. Bletchley was also on the direct GPO telephone line between Birmingham and London, which meant it was possible to establish fast communications with London. BP wartime operations were one of Britain's best-kept secrets.

The British GC and CS effort was vast and crucially, distributed across several sites. The centre of the effort was Station X. More code breaking machines needed more buildings. Outstations were set up nearby at Gayhurst Manor and Wavendon House as well as Adstock and Eastcote and Stanmore in north London.

Civilians, WRNS, WAAFS and ATS provided the skills, expertise and person power to intercept, decode, translate and understand the meaning of messages being sent between German field officers and command. The contribution of several thousand women was central to this effort.

The atmosphere of secrecy was maintained through several measures. Women were recruited after observation in basic training for 'jobs they wouldn't be allowed to speak about'. New recruits were sent a long way from home for training.

When they were sent to Bletchley they might be collected from the station in a Black Maria. They signed the official secrets act and were reminded daily never ever to speak of who they were or what they did. Security was tight, at the gate, in the huts and access was controlled across the park.

The organisational structures were developed by Gordon Welchman, a Cambridge mathematician, in 1939. The creation of separate 'huts', such as Hut 6 or Block F referred to sub-organisations rather than specific buildings. No-one knew what was being done in other parts of the Park or outstations. 

Oliver Lawn says that '... the compartmentalisation of knowledge was particular to Bletchley Park and they [the workers] knew nothing about what anyone else did'.

3.2 The first computers

In the early days, the decoding and encrypting was done manually by the male and female cryptographers. The war progressed and the amount of intercepted German communications increased.

As decoding operations increased 'it turned from a cottage industry to a production line... it was amazing the number of people who came in, top engineers... it was all so experimental to begin with that they didn't really know what they wanted... As soon as the government knew how much could be done at BP, they pumped more money in' said Mavis Batey, a cryptographer there.

The big problem was that the German's used a machine (Enigma) to encrypt their messages and changed the settings everyday. Thousands of messages were intercepted, categorised and stored. Meanwhile the operators worked hard in poor conditions to try and work out the enigma settings for each day - trying out millions of combinations before being able to decipher the intercepted messages.

Alan Turing, a Cambridge mathematician, was the genius behind the design of the first Bombe machine. The Bombe is an electro-magnetic machine based on the basic technology of the punched tape system built by the British Tabulating Machine Company in Letchworth.

But the Bombe didn't use punched tapes. The Bombe's role was to find the settings of the wheels on the German Enigma machine. It was the knowledge of these wheel settings that allowed the rest of the decoding process to be done, reducing the time taken to test all of the possible wheel settings.

In total there were 210 Bombes: 100 at Eastcote, 75 at Stanmore and smaller numbers at each of the other stations.

WRNS were the first operators, with nearly 2000 being employed by the end of the war. At the end of the war the WRNS worked with the engineers to dismantle and discard every last piece of the machines to protect the secret. Stories circulate of the last set of blue prints being hidden inside a machine and being bricked up... somewhere. But it has never been found.

The Bombe was rebuilt at Bletchley Park by a team led by John Harper and was officially switched on by the Duke of Kent on 17 July 2007. BCSWomen and some of the women veterans who took part in this project attended.

Turing went on to work with Max Newman in building Britain's first programmable electronic computer, the Colossus. Colossus was a special-purpose machine designed primarily to perform processes to decode the successor to Enigma, the Tunny machine. It was built by Tommy Flowers, a GPO engineer and the first machine was installed at Bletchley Park in 1943 in a section known as the Newmanry.