Jimmy Thirsk
Librarian turned Bletchley analyst whose study of enemy communications revealed vital clues
JIMMY THIRSK, who has died aged 104, was an intelligence analyst at Bletchley Park who at the end of the war led a protest when the codebreakers were ordered to switch to working on the communications of their erstwhile French and Russian allies.
Thirsk’s team, which was attached to Hut 6 where the German army and air force Enigma ciphers were broken, provided details of locations of German units and what they were doing, based purely on their plain text communications.
The work of Sixta (standing for Hut 6 traffic analysis) was of vital assistance to the Hut 6 codebreakers in giving them clues as to what the Enigma messages might be saying, which could be tested by the Bombe, the electro-mechanical device that Alan Turing had designed at Bletchley in 1939.
James Wood Thirsk, always known as Jimmy, was born in Hull on May 30 1914. His father, Christian Wilkie Thirsk, was a Customs & Excise officer and his mother Clara a housewife. They moved to Beverley in 1915 to avoid the threat of bombing by Zeppelins.
After leaving Beverley grammar school at 16, Thirsk moved to Great Harwood in Lancashire to take up a post as a librarian. He was called up into the Army in September 1940, serving first as an infantryman with the King’s Own Royal Regiment before being transferred into the artillery.
Once it became known that he was a librarian, he was assigned to office work, taking charge of an index of soldiers attached to Merchant Navy ships to man their guns which detailed where each soldier and his ship were at any point of time.
Thirsk transferred into the Intelligence Corps in late 1941 and was sent first to Beaumanor, near Loughborough in Leicestershire, where the traffic analysis unit was then based. Within a month of his having joined, it moved to Bletchley. In a chapter contributed to The
Bletchley Park Codebreakers, a collection of accounts by former codebreakers and historians, Thirsk described how he and his colleagues used the most innocuous German communications to build up a picture of the enemy’s war machine.
The British intercept operators logged everything said by the German signallers and used various technical measures including direction-finding to give a rough location of every radio station.
Thirsk and his colleagues would each deal with their own allocated networks, conducting “a sort of detective work” which allowed them to build up an understanding of the network and spot the many clues the Germans gave away to who they were and what they were doing.
At the end of each week, they would write a report on their network explaining precisely what it had been doing that week and all the new details they had discovered about the units involved.
“Having written the weekly reports I would get a day off-duty, which I would spend perhaps in London, Oxford, Cambridge or Bedford. Trips to the theatre or the cinema, spending hours in the bookshops, a meal at my favourite restaurant, Au petit coin de France, in Soho, were always welcome breaks.”
Initially, he and his colleagues were not told that Bletchley Park was breaking the Enigma ciphers but Gordon Welchman, the head of Hut 6, argued that giving them access to the files would allow them to deduce even more details about the German forces and their plans.
At the beginning of 1943, Welchman told Thirsk and his colleagues that Enigma was being broken on a daily basis. “It was a memorable day for all of us,” Thirsk said. “Now we had a new zest for the work, with access to a wealth of information about the German networks.
“Before we were told about Enigma, we were trying to construct a picture with a jigsaw lacking many pieces. It was possible to keep up to date knowledge of German army and air force networks and movements all over Europe and in other theatres of war as well.”
Thirsk recalled that his fellow analysts included “teachers, barristers, librarians, accountants, journalists, bank clerks, parsons’ daughters, undergraduates and graduates, male and female, who had recently completed their degrees or interrupted their university courses”.
They were given a variety of ranks from private to captain. Thirsk was a sergeant-major. His fellow analyst and girlfriend Joan Watkins was a commissioned officer. “But whenever we were doing the same work, we were totally unconcerned with our ranks.”
Army commanders took a different view and when they were moved out of their civilian billets into a new barracks, the couple were prevented from meeting up on camp.
“We were not permitted to meet in the officers’ mess or the sergeants’ mess,” Thirsk recalled. “But the Bletchley Park cafeteria was more democratic, being a place where a colonel could sit at the same table as a private.”
At the end of the war with Germany, Thirsk and his colleagues were astounded to be told that now they would be working on the communications of their erstwhile allies Russia and France.
“Many refused to take part,” he said. “We formed a group and protested. A captain whose name I do not remember attempted to justify the work, but we could not agree. ‘In that case,’ he said, ‘you are redundant’.”
Thirsk and Watkins married in September 1945. He returned to his work as a librarian, while she resumed her studies and went on to become a leading agricultural historian and a fellow of the British Academy. They had two children, a son and a daughter.
Thirsk retired in 1974 and wrote a memoir of his wartime service, Bletchley Park: An Inmate’s Story, which was remarkable in the way it downplayed his own role and focused largely on those who worked alongside him.
He also authored two other books: A Beverley Child’s Great War and Boyhood in Beverley: A Mosaic of the 1920s.
Thirsk’s wife Joan died in 2013. He is survived by his son Martin and daughter Jane.