Bletchley Park’s work on JN-25

The document that forms this chapter was written by Alan Turing and sent to the US Navy codebreaking unit, OP-20-G, in Washington, DC, probably to the celebrated cryptanalyst Mrs Agnes Driscoll. It is undated, but was probably dispatched in the autumn of 1941. Turing solved the indicating system of the principal Naval Enigma cipher, Heimisch (codenamed ‘Dolphin’ by the Government Code and Cypher School (GC & CS)), at Bletchley Park by the end of 1939. Typically, he thought Dolphin ‘could be broken because it would be so interesting to break it’ (see ‘Enigma’, p. 257).Hut 8 at Bletchley Park solved some wartime Naval Enigma signals in May and June 1940. Internal evidence shows that Turing wrote his outstanding Treatise on the Enigma around autumn 1940.GC&CS read Dolphin traffic currently, using captured keys, in June and July 1941. The resulting data provided enough cribs and other information to break Dolphin signals cryptanalytically from August onwards, within 24 to 36 hours of their transmission. Mrs Driscoll was assigned to attack Naval Enigma, with two assistants, around October 1940. However, the US Navy was then intercepting only a small proportion of the Naval Enigma signals being transmitted, and was unable to make any progress against Dolphin, especially since it could not reconstruct the wiring of Enigma’s wheels. It did not even fully understand the wheels’ noncyclometric motion, which considerably complicated any solution of Naval Enigma, in particular, since each of the special Kriegsmarine wheels VI to VIII had two notches. Notching made the wheel motion irregular, especially when a doubly notched wheel was in the middle or right-hand position. Using two doubly notched wheels could reduce Enigma’s period from its normal 16,900 (26´25´26) to 4,056 (24´13´13). In February 1941, following lengthy negotiations between the US Army and Navy, a four-man team led by Abraham Sinkov visited GC & CS. (Sinkov was accompanied by Leo Rosen, also from the US Army’s Signal Intelligence Service, and Lt. Robert Weeks and Lt. Prescott Currier, both from OP-20-G.)

The Bombe machine was a key device in the cryptanalysis of the ciphers created by the machine system widely employed by the Axis powers during the Second World War – Enigma. The Bombe machine was initially designed in Britain by scientists in primary cryptanalysis agency, the Government Code and Cypher School at Bletchley Park. The machines were then mass produced by the British Tabulating Machine Company in Britain, and by the National Cash Register Company in the United States of America. The design, development and mass production of the machine was a fraught process dependent on support from scientists and bureaucrats within the agency, but more importantly the agency was only moved to mechanise, and subsequently professionalise, this key function in its operations when met with a series of major crises. The result was an unplanned ad hoc process of designing, building and operating the machines. This was representative of the wider process of mechanisation within Bletchley Park, one of the most important and renowned technological centres to emerge in Britain during the Second World War.

The Second World War saw a major influx of mathematical talent into the areas of cryptanalysis and cryptography. This was particularly true at the UK’s Government Code and Cypher School (GCCS) at Bletchley Park. The success of introducing mathematical thinking into activities previously dominated by linguists is well studied, but the reciprocal question of how cryptography affected the field of mathematics has not been investigated as thoroughly. Although their cryptologic achievements are not as celebrated as those of Alan Turing, Bill Tutte, and Gordon Welchman, some eminent mathematicians supplemented Bletchley Park’s efforts and provided leadership and direction for mathematical research in the United Kingdom. Among their number were Ian Cassels, Sandy Green, Philip Hall, Max Newman, and Henry Whitehead. This paper considers how the experience of these and other mathematicians at Bletchley Park informed and influenced the mathematics produced in their postwar careers.

Dilly Knox, the renowned First World War codebreaker, was the first to investigate the workings of the Enigma machine after it came on the market in 1925, and he developed hand methods for breaking Enigma. What he called ‘serendipity’ was truly a mixture of careful observation and inspired guesswork. This chapter describes the importance of the pre-war introduction to Enigma that Turing received from Knox. Turing worked with Knox during the pre-war months, and when war was declared he joined Knox’s Enigma Research Section at Bletchley Park. Once a stately home, Bletchley Park had become the war station of the Secret Intelligence Service (SIS), of which the Government Code and Cypher School (GC&CS) was part. Its head, Admiral Sir Hugh Sinclair, was responsible for both espionage (Humint) and the new signals intelligence (Sigint), but the latter soon became his priority. Winston Churchill was the first minister to realize the intelligence potential of breaking the enemy’s codes, and in November 1914 he had set up ‘Room 40’ right beside his Admiralty premises. By Bletchley Park’s standards, Room 40 was a small-scale codebreaking unit focusing mainly on naval and diplomatic messages. When France and Germany also set up cryptographic bureaux they staffed them with servicemen, but Churchill insisted on recruiting scholars with minds of their own—the so-called ‘professor types’. It was an excellent decision. Under the influence of Sir Alfred Ewing, an expert in wireless telegraphy and professor of engineering at Cambridge University, Ewing’s own college, King’s, became a happy hunting ground for ‘professor types’ during both world wars—including Dillwyn (Dilly) Knox (Fig. 11.1) in the first and Alan Turing in the second. Until the time of Turing’s arrival, mostly classicists and linguists were recruited. Knox himself had an international reputation for unravelling charred fragments of Greek papyri. Shortly after Enigma first came on the market in 1925, offering security to banks and businesses for their telegrams and cables, the GC&CS obtained two of the new machines, and some time later Knox studied one of these closely.

During World War II, Bletchley Park, a former country house in Buckinghamshire, was the home of the British Government's Code and Cypher School. The small organization that arrived in August 1939 grew into a staff of more than 10,000 by 1945. The need for progressively larger and more complex accommodation necessitated a near-continuous building programme. Despite some demolitions and post-war alterations, many of the site's wartime buildings still stand.A recent programme of architectural study, landscape survey and archival research by English Heritage has provided for the first time a comprehensive overview of Bletchley's development. The sequence and functions of the standing buildings have been established, and ways in which their evolution related to the earlier (largely Victorian) landscaped park have been explored. Bletchley represents in its architecture the evolution of a cryptographic research centre from modest beginnings into a global signals intelligence centre.

The introduction of electro-mechanical encoding machines with billions of permutations at the end of the First World War brought a new challenge to code-breakers. Perhaps the greatest threat was the German Enigma machine and its far more complex big brother, the Lorenz machine. Not that this seemed to bother the British government, who were aware Polish intelligence had managed to `break' an Enigma during its testing with the German army. It did, however, bother Admiral Sir Hugh Sinclair, head of the Secret Intelligence Service (SIS/MI6) and all cryptanalysts who realised that the Polish Enigma was only `broken' until the Germans changed the machine's rotor settings, which at the time they rarely did. With some prescience, Admiral Sinclair decided to set up a joint physical base for SIS and the Government Code and Cipher School (GC&CS), settling on Bletchley Park as their new home.

Alan Turing’s visit to the US Navy Cryptanalytic Section (Op-20-G) and the US Army’s Signal Security Agency during the winter of 1942–1943 was a significant milestone in the collaboration between the British Government Code and Cypher School (GC & CS) and its US counterparts. As technical expert for the GC & CS, Turing viewed the progress of Op-20-G as it designed and developed its own Bombe and other machine aids for defeating German Enigma ciphers. Some of these machines were requested by Turing and John Tiltman for use at Bletchley Park. Not merely an observer, Turing consulted with and advised Op-20-G on Enigma-related matters before and during his visit. Obtaining clearance for Turing to view the X-system, a voice scrambler being developed at Bell Telephone Labs, required the intercession of Field Marshal Sir John Dill and a personal appeal to General George C. Marshall. It may have inadvertently contributed to the later signing of the British-United States Agreement (BRUSA) signed in May 1943. Turing’s report on the X-system was key to its acceptance and installation in London. His activities in the United States reveal him to have been an expert in all aspects of machine-based cryptanalysis who influenced the development of the US Navy’s Bombe program and possibly speech encipherment at Bell Labs.

The work of GCCS at BP has received much attention in recent years. Concentration, however, has been on the capture of Sigint by the interception services and the problems of decryption of messages in Enigma. Less attention has been placed on the documentation of the decrypts and the intelligence held by the factual indexes maintained by the Air, Military and Naval Sections. Lying behind these were the highly specialized devices which facilitated the translation and analysis of decrypted messages by providing the expansions of abbreviations common in all Sigint and the ‘equivalents’ of German and other terms. This paper describes the work of two specialist units, serving Hut 3 (Air and Military intelligence) and Hut 4 (Naval intelligence), engaged in the creation and maintenance of such devices.

The RAF Y Service and the German Air Section at Bletchley Park collaborated in producing a great deal of intelligence about GAF (German Air Force) operations in World War II. However, two errors in pre-war planning reduced this output. The first error was the decision that the Government Code and Cypher School (GC&CS) should be responsible solely for cryptography, the interpretation of Sigint to be the task of the Intelligence recipients. The second was the general assumption that the information obtainable from intercepting the low-grade codes and plain language used in the control of Air operations would only be of intelligence interest while the operations were in progress. After-the-event study of these communications by the German Air Section produced unique information needed by the RAF Commands. The Air Ministry took an unduly long time to agree that this information should be provided to them.

Alan Turing was born in Paddington, London on June 23, 1912 . His family were middle-class and well-off. He was fascinated with science from an early age and showed precocious talent, especially in the areas of chemistry and mathematics. He attended Sherbourne Public School and then King's College, Cambridge where he studied mathematics. His areas of interest at Cambridge were probability theory and mathematical logic. It was at Cambridge that he first conceptualised the Universal Turing Machine, an idea that was to evolve into the modern theory of computing. He has been referred to as the father of the computer. He worked on a cipher machine at Princeton University between 1936 and 1938. He worked for the British Government during World War II with the Government Code and Cipher School at Bletchley Park. He was ultimately the key player in deciphering the German 'Enigma' code used by its submarines during the war. After the war he took up a post in Manchester University where he continued to work on ideas of artificial intelligence. He was arrested and charged for homosexual activity in 1952 and underwent a course of oestrogen therapy. He committed suicide in 1954. He was regarded as being socially aloof and eccentric by colleagues and friends. He was interested in mathematics, chemistry and logic from an early age, to the exclusion of other activities. This paper attempts to establish whether he fulfilled the criteria for Asperger's syndrome.

On l October 1945 Turing was appointed to the newly-formed Mathematics Division of the National Physical Laboratory, his brief to design an electronic stored-program digital computer. The lectures published here, given by Turing and his assistant J.H. Wilkinson in December 1946-February 1947, add substantially to our knowledge of Turing’s design. The lectures detail the evolution of the design from Version V of early 1946 through Version VI to Version VII. On 8 December 1943, the world’s first large-scale special-purpose electronic digital computer came into operation, at the Government Code and Cypher School, Bletchley Park, England.

Experiences in researching the documentation of the intelligence (codename Ultra) produced by breaking Enigma at Government Code & Cypher School, Bletchley Park, 1939—45, are described. The major problems are identified and shown to lie in the obscurity of the associated processes, disguised as they were within general bureaucratic arrangements. This resulted in invisibility in both National Archives documents and publications in the field of military intelligence. This invisibility, along with difficulties in locating surviving veterans capable of illuminating such historical material as there is, demands detective work, serendipity and luck in addition to the normal skills of historical method in telling the story.

Bletchley Park’s workers are typically presented in the popular press and media as a small group of brilliant, if often somewhat eccentric, men employing the most modern machines to crack Axis codes. This picture has been developed since the ‘Ultra Secret’ was first revealed to the world by F. W. Winterbotham in 1974. Indeed, the preface to Winterbotham’s memoir conforms to the myth by stating that the ‘cipher breaking operation’ was ‘accomplished by a team of brilliant mathematicians and cryptographers’. 1 No individual captures this image quite like Alan Turing, who has become the archetypal Bletchley Park employee. For example, the 2014 film The Imitation Game, a biopic of Turing’s life and wartime achievements, places Turing at the centre of a small handful of cryptanalysts. 2 The film serves as an excellent example of the popular perception of the agency and will doubtless also contribute much to maintaining an inexorable focus on Turing and cryptanalysis in popular imagination. While the work of the cryptanalysts was, of course, at the epicentre of the agency’s function, it is easy to lose focus of the fact that the agency required a vast array of other forms of work in order to adequately operate. These other types of work, ranging from machine operation to cleaning, were vital support roles which facilitated the main work of the agency: cracking ciphers and reading messages.

As international tension increased, it became ever more crucial to find out as much information as possible about the thinking, activities and planning of the country’s potential enemies. Intelligence — both the machinery by which this information would be gathered, and the product of these processes, the information itself — rose up the national agenda. By the outbreak of war, understanding the enemy and thereby pre-empting hostile operations would be a key part of Britain’s wartime effort. A great deal has been written about the role of British Intelligence during the war, in particular the Bletchley Park (the Government Code and Cypher School, GCCS) phenomenon (see, for example, Hinsley 1979–90; Lewin 1978; Welchman 1982; Hinsley and Stripp 1994; Patterson 2008). None of this, however, has engaged with what we might call the ‘foreignness’ of this intelligence, the fact that most of the information accessed in its original form was in a foreign language and hence would have to be translated into English in order to become useful intelligence material. Listening stations dotted around the coast would be intercepting messages which were in the foreign language and had to be accurately taken down and translated. As one observer described the situation early on: [T]he excitement of realizing that they were at long last monitoring radio-telephony messages from German pilots and their ground stations was somewhat marred by the fact that no one at the unit spoke German sufficiently well to understand what was being said. (Clayton 1980: 29).

The code-breaking activities of the British Government Code and Cipher School at Bletchley Park have dominated our understanding of the secret war to infiltrate the message system of the German forces in Europe between 1939 and 1945. This is the story of the US Navy's response to the need to gain intelligence to win the battle of the Atlantic in 1941 and 1942, the competitive development of mechanical code-breaking systems known as Bombes, and the contributions of NCR engineer Joseph Desch and 600 Navy WAVES (Women Appointed for Volunteer Emergency Service).