Bletchley Park & Enigma

Today we visited Bletchley Park, located in Milton Keynes, a little over an hour north. During World War II it was the home of the Government Code & Cipher School (GC&CS) which was the nexus for allied code breaking whose most famous achievement (although arguably perhaps not the most important) was breaking the German Enigma.

It is a fascinating visit and we were fortunate to catch a guided tour which provided interesting insight. And today a member of the group was a lady in her 80s who recorded intercepts in Station Y (more later).

GC&CS (or Golf, Cheese & Chess Society as it was colloquially known) was sited at Bletchley Park in 1939. It housed both code breakers and intelligence analysts. The most recognisable element of Bletchley Park is the rather confused architectural styling of the mansion’s façade. However, most of the work was performed in huts. Each hut was paired; one of the code breakers and the other for the intelligence analysts whose job it was to interpret the messages. There were pairs of huts for different communication stream. For example, the Army & Airforce, and one for Naval intelligence.

Bletchley Park was chosen for a number of reasons. The motivation was to relocate key services out from London. Bletchley Park is located almost equidistant from London and from both Cambridge and Oxford (from where mathematicians and linguist were drawn). Importantly there was an existing major telephone exchange in the area. This allowed the government to add the enormous communication infrastructure required to receive and disseminate the intelligence without drawing attention to the location.

There were many outstanding achievements at GC&CS (aside: the “School” in the name was used as disinformation so as to disguise the true intent of the outfit). One was leveraging the concept of attacking machine ciphers with machines. This was led by Alan Turing who, due to his work on analytical engines, is now considered the father of computers (what would John von Neumann say?). GC&CS turned code breaking into a factory. Code breaking machines (such as the Bombe and Colossus) allowed massively parallel analytical attacks on cipher intercepts leading to obtaining the all important keys leading to the decipher within hours.

Intelligence arrived in Bletchley Park from intercept points known as Station Y. Due to the speed of the German Blitzkrieg communication with the front lines was wireless. Such communications were intercepted by Station Y in either fixed location or via mobile units that were positioned near the action. Intercepts found their way to GC&CS either by electronic communication or by motorcycle courier. The intelligence product was referred to as “Ultra” and was provided directly to Churchill.

On site are a number of Enigma machines. Rather than a single type, Enigma is a family of encryption devices. There is also a working replica of the Bombe. Of most interest to me was the rebuilt Colossus Mark II. This is nearing completion after 12 years of work by a dedicated team of enthusiasts. These are arguably the first computers and were used to decipher the German Lorenz SZ 40 – used for the most sensitive traffic. It reads paper tape representing intercepted teleprinter communications at a rate of 5000 characters per second. We stepped into the room housing the working replica and was hit both by the warmth and strangely familiar smell of valves (all 2500 of them – generating 1.5kW of heat). Lights on a panel – reminiscent of an old science fiction film – showed the progress of the machine.

Interestingly the Colossus was secret until the mid 1970s so its role both in computing and cryptanalyst terms was not known for a long time after the war.

Photos here.