Editing Alan Turing (section)

===Hut 8 and the naval Enigma===
[[File:Turing-statue-Bletchley 14.jpg|thumb|upright|Statue of Turing holding an Enigma machine by [[Stephen Kettle]] at Bletchley Park, commissioned by [[Sidney Frank]], built from half a million pieces of Welsh slate<ref>{{cite web |title=Bletchley Park Unveils Statue Commemorating Alan Turing |url=http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |access-date=30 June 2007 |archive-url=https://web.archive.org/web/20070630083823/http://www.bletchleypark.org.uk/news/docview.rhtm/454075 |archive-date=30 June 2007 |url-status=live }}</ref>]]

Turing decided to tackle the particularly difficult problem of cracking the [[Cryptanalysis of the Enigma#German Naval Enigma|German naval use of Enigma]] "because no one else was doing anything about it and I could have it to myself".<ref name=MahonP14>{{Harvnb|Mahon|1945|p=14}}</ref> In December 1939, Turing solved the essential part of the naval [[Enigma machine#Indicator|indicator]] system, which was more complex than the indicator systems used by the other services.<ref name=MahonP14 /><ref>{{Harvnb|Leavitt|2007|pp=184–186}}</ref>

That same night, he also conceived of the idea of ''[[Banburismus]]'', a sequential statistical technique (what [[Abraham Wald]] later called [[sequential analysis]]) to assist in breaking the naval Enigma, "though I was not sure that it would work in practice, and was not, in fact, sure until some days had actually broken".<ref name=MahonP14 /> For this, he invented a measure of weight of evidence that he called the ''[[Ban (unit)|ban]]''. ''Banburismus'' could rule out certain sequences of the Enigma rotors, substantially reducing the time needed to test settings on the bombes.<ref>{{Cite journal|last=Gladwin|first=Lee|date=Fall 1997|title=Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II|url=https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|journal=Prologue Magazine|volume=Fall 1997|pages=202–217|via=National Archives|access-date=13 April 2019|archive-url=https://web.archive.org/web/20190626211657/https://www.archives.gov/files/publications/prologue/1997/fall/turing.pdf|archive-date=26 June 2019|url-status=live}}</ref> Later this sequential process of accumulating sufficient weight of evidence using decibans (one tenth of a ban) was used in [[cryptanalysis of the Lorenz cipher]].<ref>{{Citation | last1 = Good | first1 = Jack | author-link = I. J. Good | last2 = Michie | first2 = Donald | author2-link = Donald Michie | last3 = Timms | first3 = Geoffrey | title = General Report on Tunny: With Emphasis on Statistical Methods | year = 1945 | id = UK Public Record Office HW 25/4 and HW 25/5 | url = http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | at = Part 3 Organisation: 38 Wheel-breaking from Key, Page 293 | access-date = 13 April 2019 | archive-url = https://web.archive.org/web/20190421091539/http://www.alanturing.net/turing_archive/archive/t/t15/TR15-018.html | archive-date = 21 April 2019 | url-status = live }}</ref>

Turing travelled to the United States in November 1942 and worked with US Navy cryptanalysts on the naval Enigma and bombe construction in Washington.<ref>{{Harvnb|Hodges|1983|pp=242–245}}</ref><ref>{{Cite web |title=Alan Turing's Report from Washington, 1942 |url=https://www.turing.org.uk/sources/washington.html |access-date=12 July 2023 |website=www.turing.org.uk |archive-date=12 July 2023 |archive-url=https://web.archive.org/web/20230712083844/https://www.turing.org.uk/sources/washington.html |url-status=live }}</ref> He also visited their [[United States Naval Computing Machine Laboratory|Computing Machine Laboratory]] in [[Dayton, Ohio]].<ref>{{Cite web |title=Alan Turing's Dayton Report, 1942 |url=https://www.turing.org.uk/sources/dayton123.html |access-date=12 July 2023 |website=www.turing.org.uk}}</ref>

Turing's reaction to the American bombe design was far from enthusiastic:

{{blockquote|text=The American Bombe programme was to produce 336 Bombes, one for each wheel order. I used to smile inwardly at the conception of Bombe hut routine implied by this programme, but thought that no particular purpose would be served by pointing out that we would not really use them in that way.

Their test (of commutators) can hardly be considered conclusive as they were not testing for the bounce with electronic stop finding devices. Nobody seems to be told about rods or offiziers or banburismus unless they are really going to do something about it.<ref>{{Cite journal |last=Turing |first=Alan M. |year=2001 |journal=Cryptologia |volume=25 |issue=1 |pages=1–10 |doi=10.1080/0161-110191889734 |title=Visit to National Cash Register Corporation of Dayton, Ohio |s2cid=14207094 }}</ref>|source=}}

During this trip, he also assisted at [[Bell Labs]] with the development of [[secure speech]] devices.<ref>{{Harvnb|Hodges|1983|pp=245–253}}</ref> He returned to Bletchley Park in March 1943. During his absence, [[Colonel Hugh O'Donel Alexander|Hugh Alexander]] had officially assumed the position of head of Hut 8, although Alexander had been ''de facto'' head for some time (Turing having little interest in the day-to-day running of the section). Turing became a general consultant for cryptanalysis at Bletchley Park.<ref>{{Cite web|url=https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|title=Marshall Legacy Series: Codebreaking – Events|website=marshallfoundation.org|access-date=7 April 2019|archive-url=https://web.archive.org/web/20190407030638/https://www.marshallfoundation.org/newsroom/marshall-legacy-series/codebreaking/|archive-date=7 April 2019|url-status=live}}</ref>

Alexander wrote of Turing's contribution:

{{blockquote|There should be no question in anyone's mind that Turing's work was the biggest factor in Hut 8's success. In the early days, he was the only cryptographer who thought the problem worth tackling and not only was he primarily responsible for the main theoretical work within the Hut, but he also shared with Welchman and Keen the chief credit for the invention of the bombe. It is always difficult to say that anyone is 'absolutely indispensable', but if anyone was indispensable to Hut 8, it was Turing. The pioneer's work always tends to be forgotten when experience and routine later make everything seem easy and many of us in Hut 8 felt that the magnitude of Turing's contribution was never fully realised by the outside world.<ref>{{Harvnb|Alexander|circa 1945|p=42}}</ref>}}