John Herivel
John William Jamieson Herivel (29 August 1918 – 18 January 2011)[1] was a British science historian and World War II codebreaker at Bletchley Park.
[3] It was based on Herivel's insight into the habits of German operators of the Enigma cipher machine that allowed Bletchley Park to easily deduce part of the daily key.
For a brief but critical period after May 1940, the Herivel tip in conjunction with "cillies" (another class of operator error) was the main technique used to solve Enigma.
After the war, Herivel became an academic, studying the history and philosophy of science at Queen's University Belfast, particularly Isaac Newton, Joseph Fourier, Christiaan Huygens.
In retirement, he wrote an autobiographical account of his work at Bletchley Park entitled Herivelismus and the German Military Enigma.
In 1937 he was awarded a Kitchener Scholarship to study mathematics at Sidney Sussex College, Cambridge, where his supervisor was Gordon Welchman.
[5][6] Welchman recruited Herivel to the Government Code and Cypher School (GC&CS) at Bletchley Park.
Welchman worked with Alan Turing in the newly formed Hut 6 section created to solve Army and Air Force Enigma.
[7] Herivel, then aged 21, arrived at Bletchley on 29 January 1940,[8] and was briefed on Enigma by Alan Turing and Tony Kendrick.
[9] At the time that Herivel started work at Bletchley Park, Hut 6 was having only limited success with Enigma-enciphered messages, mostly from the Luftwaffe Enigma network known as "Red".
[7] The process was slow, however, Herivel was determined to find a method to improve their attack, and he would spend his evenings trying to think up ways to do so.
[11] Herivel had an insight in February 1940 that some lazy German code clerks might give away the Enigma's ring settings (Ringstellung) in their first message of the day.
From September 1938, he would use an initial position to encrypt the indicator and send it in clear, followed by the message key that had been enciphered at that setting.
[8] Hut 6 began looking for the effect predicted by the Herivel tip and arranged to have the first messages of the day from each transmitting station to be sent to them early.
Fortunately for the codebreakers, the pattern predicted by the Herivel tip began to manifest itself soon after on 10 May, when the Germans invaded the Netherlands and Belgium.
The Herivel tip was used in combination with another class of operator mistake, known as "cillies", to solve the settings and decipher the messages.
[18][22] The Herivel tip was used for several months until specialised codebreaking machines designed by Alan Turing, the so-called "bombes", were ready for use.
Gordon Welchman wrote that the Herivel tip was a vital part of breaking Enigma at Bletchley Park.
After the end of the war, Herivel taught mathematics in a school for a year,[6] but he found he could not handle the "rumbustious boys".
