Alan Turing: The Enigma, Andrew Hodges. London: Vintage Books, 1983, 2012 (publisher’s link is for an updated edition by Princeton University Press, 2015).

Summary: Perhaps the definitive account of the brilliant mathematician, cryptanalyst, and computer scientist, Alan Turing, who was prosecuted for his homosexuality, not long before the end of his life due to cyanide poisoning.

The title of this work reflects both the important, and long secret work, Turing did to decrypt German transmissions encrypted by their Enigma machine, for which he was awarded an OBE, and that Turing, in life and death was something of an enigma, even to those closest to him. Andrew Hodges wrote this tour de force of a biography, dealing both with the singular scientific accomplishments of his life and the struggles he faced in his time as a gay man. As both a mathematician and a leader in the London Gay Liberation Front, Hodges was uniquely suited to write this work and it reflects these qualifications.

This is a complete biography, from his earliest years. We learn of the early roots of Turing’s interest in the function of the mind, and the shift to a materialist focus after the death of his close friend Christopher Morcom, who was his first love. This would be reflected in his efforts to create machine intelligence that worked like human intelligence. He was elected a fellow at King’s College for his proof in 1935. of the central limit theorem, which, unknown to him, had been previously proven, although his proof used a different and innovative approach. A year later, he published his most famous paper, On Computable Numbers, in which he proposed a hypothetical universal computing machine (often referred to as a Turing machine) that laid the theoretical basis for computers. Once again, another researcher, Alonzo Church, had addressed the same problem, again by a different approach. And so Turing went to study with Church at Princeton, building an electro-mechanical binary multiplier while he was there.

This reveals another theme in Turing’s life. He was not only interested in the theoretical but also in the engineering aspects of realizing the machines of which he theorized. This led to the next major involvement of Turing, during the war, in the decryption of German radio transmissions encrypted with their Enigma machines, thought to be unbreakable. Building on Polish efforts, he not only developed innovative statistical methods to break the code but developed the bombes, a type of computer, that would radically speed up the process. It was for this work, kept secret for many years, that he received the OBE (Officer of the Most Excellent Order of the British Empire) from King George VI.

Hodges also covers his post-war work on computers and his further interest in artificial intelligence, resulting in his paper on “Computing Machinery and Intelligence” with his proposal of an experiment that later became known as the “Turing Test.” His ideas of universal machines, that could be used for various computational tasks, led him to write some of the earliest programs, including a primitive chess program.

The account of Turing’s scientific work is interwoven with his relationships with men, his brief engagement to Joan Clark, which he realized would not work out, and the relationship that led to Turing facing criminal charges for his homosexuality. There is extensive background offered as well as discussion of the legal and social conventions of the day. Perhaps the most troubling, and some have suggested it contributed to Turing’s death, was the agreement, in lieu of a prison term, that Turing would undergo estrogen treatments to suppress his homosexual inclinations. I also found it puzzling why Turing incriminated himself with the police investigating a burglary of his home by a friend of his lover.

It seemed to reflect an “out of touchness” that manifested itself in everything from his unawareness of similar research to his own, to his inability to manage others well. He seemed to expect people to act logically as he would, and was surprised when they did not. My sense is that he thought it should be no big deal to love the people he wanted to love, and I think was genuinely surprised that even though such behavior was illegal, the police would look the other way.

His death in June 1954 was another enigma covered by Hodges. It was ruled a suicide by cyanide poisoning through an apple dipped in a cyanide solution and then partially eaten, found by his bedside where he was found dead. He had cyanide on the premises, using it in a process to electroplate gold onto silver spoons. Oddly, the apple was never tested, there seemed no preparations for suicide, and it was speculated that this was an accident during his experiments, either from inhalation or grains on his fingers. Supporting suicide was the way the body was composed on his bed. An enigma.

The book goes into fine detail with his life, reflecting a huge amount of research, due to the limited material left by Turing. This is a strength and weakness. Included in the detail are extensive mathematical and engineering discussions that are heavy going for those unacquainted with these fields. I estimate that probably at least 100 pages of text might be cut out if these were summarized more succinctly.

Hodges work reveals not only the enigma but the genius of Turing. Subsequent to the initial publication of this work in 1983, Prime Minister of Great Britain Gordon Brown in 2009 issued a statement apologizing for the “appalling” way Turing was treated. In August 2014, Queen Elizabeth pronounced a royal pardon of Turing in August 2014 and a law exonerating all men charged with “indecency” was passed in 2017, informally known as “Alan Turing’s law.” These actions removed the cloud hanging over the genius whose theoretical and practical work laid the groundwork for the computer on which I write this review and the “behind-the-scenes” work so crucial in the fight against Germany in World War 2, especially in ending the depredations on Allied shipping. It would not surprise me that this biography played an important part in the recognition of the importance of his work, even as it served as the basis of the film The Imitation Game.