Colossus electronic digital computer, 1943 (Catalogue ref: FO 850/234)

15 May 2012

To commemorate the centenary of of Alan Turing's birth, GCHQ (Government Communications Headquarters) has released two of his mathematical research papers, believed to have been written at Bletchley Park during the Second World War, to The National Archives. These records are now available to download.

'Helped turn the tide of war'

'Paper on Statistics of Repetitions' and 'The Applications of Probability to Crypt' were written in an era when typographical errors would be corrected by hand and mathematical notation handwritten.

In the first, 'Paper on Statistics of Repetitions' (HW 25/37), Turing works out the best statistical means of testing whether two cipher messages use the same key in parts of the message: very important in the exploitation of such messages at Bletchley Park.

The second, longer, paper (HW 25/38) demonstrates that Turing was determined to apply rigorous probability analysis to a wide range of cryptanalytic problems of the day. A particular highlight is where Turing uses life expectancy to examine conditional probability. The associated example, "Hitler is now of age 52", suggests that the paper was written between April 1941 and April 1942. Bletchley Park's output of decrypts was almost certainly enabled by the techniques in this paper. 

A spokesperson for GCHQ said: 'We are delighted to release these papers showing more of Alan Turing's pioneering research during his time at Bletchley Park. It was this type of research that helped turn the tide of war and it is particularly pleasing that we are able to share these papers during this centenary year.'

View and download the papers

You can find and order the records HW 25/37 and HW 25/38 in Discovery, our new catalogue.