There’s a lovely piece of biographical detail in The Guardian‘s obituary of Belfast-born science historian, and former World War II codebreaker at Bletchley Park, John W. Herivel who died on 18 January 2011, aged 92. From The Guardian obituary
Born in Belfast, Herivel had a civil servant father and was educated at Methodist College, from where, in 1937, he won a scholarship to Sidney Sussex College, Cambridge. He had a strong sense of humour. Unable for security reasons to tell one potential employer about his work at Bletchley, he claimed to have spent the war as a sanitary inspector. In fact, he had embarked on a DPhil after gaining his degree in mathematics when he was recruited as a codebreaker, but lost interest in completing it after the war. Instead, he taught mathematics at Campbell college, Belfast, but finding the boys difficult to control, went on to Queen’s University Belfast, as a mathematics lecturer. When the university started teaching the history and philosophy of science he moved to that discipline.
His wife, Elizabeth Jones, also worked at Bletchley, but because of the tight security rules they did not speak until she spotted him sitting in a tea room in Portrush shortly after the war and went across to say hello. Herivel subsequently confessed that although they had never met at Bletchley, he recognised her immediately, having often admired her as she cycled around the local area. They married in 1947.
And from a tribute at the Bletchley Park website
The fascinating aspect of John Herivel’s achievement is that although the exploitation of his insight depended on a mathematical mind and a detailed knowledge of the Enigma machine, the concept itself did not rely on mathematics at all, but was a brilliant example of lateral thinking or what is now called “thinking outside the box”. John had a strong poetic and romantic streak in him (he wrote poetry and read historical romances) and it was surely this which inspired him that evening in 1940.
As to the significance of ‘The Herivel Tip’, it is sometimes supposed that it was only needed during the vital period of the Battle of Britain, until the ‘bombes’ started to come on stream in the autumn of 1940. But this is not so. Even after the bombes became operative, there was still the need to reduce the number of variables before the ‘bombes’ were used, added to which there was always pressure on ‘bombe time’, with the urgent needs of Hut 8 (naval Enigma) often having to take precedence over the needs of Hut 6, a situation which continued for the duration of the war. In narrowing the variables, the constant breaking of the ‘Red’ in the summer of 1940 via the ‘Herivel Tip’ enabled Milner-Barry and his team to develop a series of ‘cribs’ to help in the breaking of the ‘Red’. So the vital importance of ‘The Herivel Tip’ long outlasted the summer of 1940, critical though that was. As Milner-Barry (Deputy Head of Hut 6 and later Head following Welchman) wrote at the end of the war (National Archives HW43/70), “I can well remember most vividly the roars of excitement, the standing on chairs, and the waving or order papers, which greeted the first breaking of the ‘Red’ by hand in the middle of the Battle of France. It was never surpassed….the greatest event of all”. Herivel was not present when this happened (24 hour shifts were being worked) but when he arrived later that day, Welchman was waiting for him. “Herivel”, he said, “this will not be forgotten!” It was only later that Herivel realised why the ‘Tip’ had worked in May 1940 but not before, and why it continued to work thereafter. This was because on 10 May, the phoney war came to an end, the Germans invaded France, and as a result there was a huge increase in the amount of Enigma traffic and the urgency of communication, meaning that the chances of enough Enigma operators taking shortcuts and thus producing a ‘cluster’ were dramatically increased.