The bombe searched for the correct settings of the Enigma rotors, and required a suitable "crib": a piece of matching plaintext and ciphertext. For each possible setting of the rotors, the bombe performed a chain of logical deductions based on the crib, implemented electrically. The bombe detected when a contradiction had occurred, and ruled out that setting, moving onto the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. Turing's bombe was first installed on 18 March 1940. Over 200 bombes were in operation by the end of the war.

Hut 8 and Naval Enigma

In the spring of 1941, Turing proposed marriage to fellow Hut 8 co-worker Joan Clarke, although the engagement was broken off by mutual agreement in the summer.

In July 1942, Turing devised a technique termed Turingismus or Turingery for use against the Lorenz cipher. A frequent misconception is that Turing was a key figure in the design of the Colossus computer; this was not the case.Copeland, 2006, pp. 382-383

Turing travelled to the United States in November 1942 and liaised with US Navy cryptanalysts on Naval Enigma and bombe construction in Washington, and assisted at Bell Labs with the development of secure speech devices. He returned to Bletchley Park in March 1943. During his absence, Hugh Alexander had 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.

In the latter part of the war, teaching himself electronics at the same time, Turing undertook (assisted by engineer Donald Bayley) the design of a portable machine codenamed Delilah to allow secure voice communications. Intended for different applications, Delilah lacked capability for use with long-distance radio transmissions, and was completed too late to be used in the war. Though Turing demonstrated it to officials by encrypting/decrypting a recording of a Winston Churchill speech, Delilah was not adopted for use.

In 1945, Turing was awarded the OBE for his wartime services.

Early computers and the Turing Test

From 1945 to 1947 he was at the National Physical Laboratory, where he worked on the design of ACE (Automatic Computing Engine). He presented a paper on February 19, 1946, which was the first complete design of a stored-program computer in Britain. Although he succeeded in designing the ACE, there were delays in starting the project and he became disillusioned. In late 1947 he returned to Cambridge for a 'sabbatical' year. While he was at Cambridge, ACE was completed in his absence and executed its first program on May 10, 1950. In 1949 he became deputy director of the computing laboratory at the University of Manchester, and worked on software for one of the earliest true computers — the Manchester Mark I. During this time he continued to do more abstract work, and in "Computing machinery and intelligence" (Mind, October 1950), Turing addressed the problem of artificial intelligence, and proposed an experiment now known as the Turing test, an attempt to define a standard for a machine to be called "sentient".

In 1948, Turing, working with his former undergraduate colleague, D.G. Champernowne, began writing a chess program for a computer that did not yet exist. In 1952, lacking a computer powerful enough to execute the program, Turing played a game in which he simulated the computer, taking about half an hour per move. The game was recorded; the program lost to a colleague of Turing, Alick Glennie, however, it is said that the program won a game against Champernowne's wife.

Pattern formation and mathematical biology

Prosecution for homosexual acts and Turing's death

In 1954, he died of cyanide poisoning, apparently from a cyanide-laced apple he left half-eaten. The apple itself was never tested for contamination with cyanide, and cyanide poisoning as a cause of death was established by a post-mortem. Most believe that his death was intentional, and the death was ruled a suicide. It is rumoured that this method of self-poisoning was in tribute to Turing's beloved film Snow White and the Seven Dwarfs. His mother, however, strenuously argued that the ingestion was accidental due to his careless storage of laboratory chemicals. Friends of his have said that Turing may have killed himself in this ambiguous way quite deliberately, to give his mother some plausible deniability. The possibility of assassination has also been suggested, owing to Turing's involvement in the secret service and the perception of Turing as a security risk due to his homosexuality.

In the book, Zeroes and Ones, author Sadie Plant speculates that the rainbow Apple logo with a bite taken out of it was a homage to Turing. This is unlikely as Gilbert Baker's rainbow pride flag, a gay pride emblem, was designed two years after the Apple logo, thus negating the possibility of it referring to Turing's sexuality.

Posthumous recognition

In 1994 a stretch of the Manchester city inner ring road was named Alan Turing Way.

On 23 June 1998, on what would have been Turing's 86th birthday, Andrew Hodges, his biographer, unveiled an official English Heritage Blue Plaque on his childhood home in Warrington Crescent, London, now the Colonnade hotel [http://www.blueplaque.com/detail.php?plaque_id=348.

A statue of Turing was unveiled in Manchester

on June 23 2001. It is in Sackville Park, between the University of Manchester building on Whitworth Street and the Canal Street 'gay village'. To mark the 50th anniversary of his death, a memorial plaque was unveiled at his former residence, Hollymeade, in Wilmslow on June 7 2004.

The Alan Turing Institute was initiated by UMIST and University of Manchester in Summer 2004.

A celebration of Turing's life and achievements was held at the University of Manchester on 5 June 2004; it was arranged by the British Logic Colloquium and the British Society for the History of Mathematics.

On October 28 2004 a bronze statue of Alan Turing sculpted by John W. Mills was unveiled at the University of Surrey ^*. The statue marks the 50th anniversary of Turing's death. It portrays Turing carrying his books across the campus.

Holtsoft produces a programming language named for Turing. The language is designed for beginner programmers and has no direct access to the hardware.

The Polytechnic University of Puerto Rico named a computer laboratory for graduate studies the Turing Lab.

The University of Texas at Austin has an honours computer science program named the Turing Scholars.

The Plymouth State University of New Hampshire has named the server used by the computer science department after Turing.

The Boston GLBT pride organization, http://www.bostonpride.org/, named Turing their 2006 Honorary Grand Marshal

Istanbul Bilgi University organizes an annual conference on the theory of computation called Turing Days.

Carnegie Mellon University has a granite bench, situated in The Hornbostel Mall, with the name "Alan Turing" carved across the top, "Read" down the left leg, and "Write" down the other.

Turing biographies

• Turing's mother, Sara Turing, who survived him by many years, wrote a biography of her son.
• Andrew Hodges wrote a definitive biography Alan Turing: The Enigma in 1983 (see references below).
• The play Breaking the Code by Hugh Whitemore is about the life and death of Turing. In the original West End and Broadway runs, the role of Turing was played by Derek Jacobi, who also played Turing in a 1995 television adaptation of the play.

Turing in fiction

• Turing appears as a character in Neal Stephenson's Cryptonomicon.
• In another one of Stephenson's books, The Diamond Age, there is an intuitive explanation of recursion, important to Turing's and related work on computability, put into the format of a child's book.
• An FBI agent named Alan Turing made an appearance in the webcomic Questionable Content as a homage to Turing.
• Mentioned in Enigma by Robert Harris, but never enters the narrative of the book.
• A young Alan Turing introduces the title character to Gödel's first incompleteness theorem in Apostolos Doxiadis's novel Uncle Petros and Goldbach's Conjecture.
• In the 1989 Doctor Who serial The Curse of Fenric, the character of Dr. Judson is based on Turing. Turing himself is a narrator of the Doctor Who spin-off novel The Turing Test by Paul Leonard.
• Greg Egan's novella, Oracle, is about an alternate universe version of Turing
• In Arthur C. Clarke's Odyssey Two, the sequel to A Space Odyssey (novel), the stoic Dr. Chandra, the programmer who created HAL 9000, has a completely spartan cubicle except for a photo of Turing beside his computer screen.
• In John Banville's The Untouchable, the character Alastair Sykes is modeled on Alan Turing.
• In the novel Neuromancer by William Gibson, there is a police force called the Turing Police designed to crack down on computers acquiring too much intelligence.

See also

• List of gay, lesbian or bisexual people
• Alan Turing's Unorganized Machines

Footnotes