Biography of Alan Turing, Code-Breaking Computer Scientist

Portrait of Alan Turing at age 16
Portrait of Alan Turing, 1928.

 Courtesy of the Turing Digital Archive.

Alan Mathison Turing (1912 –1954) was one of England's foremost mathematicians and computer scientists. Because of his work in artificial intelligence and codebreaking, along with his groundbreaking Enigma machine, he is credited with ending World War II.

Turing's life ended in tragedy. Convicted of "indecency" for his sexual orientation, Turing lost his security clearance, was chemically castrated, and later committed suicide at age 41.

Early Years and Education

Alan Turing was born in London on June 23, 1912, to Julius and Ethel Turing. Julius was a civil servant who worked in India for much of his career, but he and Ethel wanted to raise their children in Britain. Precocious and gifted as a child, Alan's parents enrolled him in the Sherborne School, a prestigious boarding school in Dorset, when he turned thirteen. However, the school's emphasis on a classical education didn't mesh well with Alan's natural inclination towards math and science.

After Sherborne, Alan moved on to university at King's College, Cambridge, where he was allowed to shine as a mathematician. At just 22 years old, he presented a dissertation that proved the central limit theorem, a mathematical theory that implies that probability methods such as bell curves, which work for normal statistics, can be applied to other types of problems. In addition, he studied logic, philosophy, and cryptanalysis.

Over the next few years, he published numerous papers on mathematical theory, as well as designing a universal machine – later called the Turing machine – which could perform any possible math problem, as long as the problem was presented as an algorithm.

Turing then attended Princeton University, where he received his PhD. 

Codebreaking at Bletchley Park

During World War II, Bletchley Park was the home base of British Intelligence's elite codebreaking unit. Turing joined the Government Code and Cypher School and in September 1939, when war with Germany began, reported to Bletchley Park in Buckinghamshire for duty.

Shortly before Turing's arrival at Bletchley, Polish intelligence agents had provided the British with information about the German Enigma machine. Polish cryptanalysts had developed a code-breaking machine called the Bomba, but the Bomba became useless in 1940 when German intelligence procedures changed and the Bomba could no longer crack the code.

Turing, along with fellow code-breaker Gordon Welchman, got to work building a replica of the Bomba, called the Bombe, which was used to intercept thousands of German messages every month. These broken codes were then relayed to Allied forces, and Turing's analysis of German naval intelligence allowed the British to keep their convoys of ships away from enemy U-boats.

Before the war ended, Turing invented a speech scrambling device. He named it Delilah, and it was used to distort messages between Allied troops, so that German intelligence agents could not intercept information.

Although the scope of his work wasn't made public until the 1970s, Turing was appointed as an Officer of the Order of the British Empire (OBE) in 1946 for his contributions to the codebreaking and intelligence world.

Artificial Intelligence

In addition to his codebreaking work, Turing is regarded as a pioneer in the field of artificial intelligence. He believed that computers could be taught to think independently of their programmers, and devised the Turing Test to determine whether or not a computer was truly intelligent.

The test is designed to evaluate whether the interrogator can figure out which answers come from the computer and which come from a human; if the interrogator can't tell the difference, then the computer would be considered "intelligent."

Personal Life and Conviction

In 1952, Turing began a romantic relationship with a 19-year-old man named Arnold Murray. During a police investigation into a burglary at Turing's home, he admitted that he and Murray were involved sexually. Because homosexuality was a crime in England, both men were charged and convicted of "gross indecency." 

Turing was given the option of a prison sentence or probation with "chemical treatment" designed to reduce the libido. He chose the latter, and underwent a chemical castration procedure over the next twelve months.

The treatment left him impotent and caused him to develop gynecomastia, an abnormal development of breast tissue. In addition, his security clearance was revoked by the British government, and he was no longer permitted to work in the intelligence field.

Death and Posthumous Pardon

In June 1954, Turing's housekeeper found him dead. A post-mortem examination determined that he had died of cyanide poisoning, and the inquest ruled his death as suicide. A half-eaten apple was found nearby. The apple was never tested for cyanide, but it was determined to be the most likely method used by Turing.

In 2009, a British computer programmer began a petition asking the government to posthumously pardon Turing. After several years and numerous petitions, in December 2013 Queen Elizabeth II exercised the privilege of royal mercy, and signed a pardon overturning Turing's conviction.

In 2015, Bonham's auction house sold one of Turing's notebooks, containing 56 pages of data, for a whopping $1,025,000.

In September 2016, the British government expanded Turing's pardon to exonerate thousands of other people who were convicted under the indecency laws of the past. The process is informally known as the Alan Turing Law.

Alan Turing Fast Facts

  • Full Name: Alan Mathison Turing
  • Occupation: Mathematician and cryptographer
  • Born: June 23, 1912 in London, England
  • Died: June 7, 1954 in Wilmslow, England 
  • Key Accomplishments: Developed a code-breaking machine that was essential to the Allied powers' victory in World War II