Alan Turing

Alan Turing (1912–1954) was a British mathematician, cryptanalyst, and logician whose breakthrough work at Bletchley Park in deciphering Nazi Germany's Enigma machine helped turn the tide of World War II, and whose theoretical concepts laid the foundation for modern computer science and artificial intelligence.

Inventing the Theoretical Computer at Twenty-Four

Born in London while his father was on leave from the Indian Civil Service, Turing displayed extraordinary mathematical gifts from an early age—famously cycling sixty miles alone to reach his boarding school on the first day of the 1926 General Strike. Studying mathematics at King's College, Cambridge, he was elected a fellow at age twenty-two. In 1936, at just twenty-four, he published his seminal paper On Computable Numbers, with an Application to the Entscheidungsproblem.

Years before any electronic digital computer was built, Turing conceived of an abstract device—now known as the 'Universal Turing Machine'—capable of performing any conceivable mathematical computation by reading and writing symbols on a strip of tape according to stored instructions. This insight that a single hardware machine could run endlessly different programs became the fundamental principle of all modern computers.

Bletchley Park and Breaking the Enigma Cipher

After earning his doctorate at Princeton University, Turing reported to the Government Code and Cypher School at Bletchley Park on September 4, 1939, the day after Britain declared war on Germany. German armed forces relied on the Enigma cipher machine, whose rotating scrambler wheels and plugboard generated over 158 quintillion possible settings, reset every day at midnight.

Building on earlier Polish cryptanalysis, Turing realized that only an automated machine could search through the astronomical number of combinations fast enough before the settings changed again. He designed the 'Bombe,' an electromechanical cabinet of spinning drums that used predictable German phrases (known as 'cribs,' such as routine weather reports) to rapidly eliminate contradictory rotor settings. As head of 'Hut 8,' Turing also cracked the far more complex Naval Enigma used by German U-boat wolfpacks, enabling Allied convoys to evade submarine ambushes during the Battle of the Atlantic. Historians estimate that Bletchley Park's 'Ultra' intelligence shortened the war in Europe by two to four years and saved over fourteen million lives.

Pioneer of Artificial Intelligence and Royal Pardon

Because wartime codebreaking remained classified for decades, Turing's wartime heroism was unknown to the public during his lifetime. After the war, he designed the Automatic Computing Engine (ACE) at the National Physical Laboratory and worked on early stored-program computers at the University of Manchester. In his landmark 1950 paper Computing Machinery and Intelligence, he opened with the question 'Can machines think?' and introduced the 'Imitation Game'—now known as the Turing Test—as a benchmark for machine intelligence.

In 1952, while reporting a burglary at his home, Turing acknowledged a relationship with another man and was convicted of 'gross indecency' under laws that criminalized homosexuality in Britain. Stripped of his security clearance and subjected to court-ordered hormone injections (chemical castration) as an alternative to prison, Turing died at his home in Wilmslow on June 7, 1954, at age forty-one from cyanide poisoning, with a half-eaten apple found beside his bed. Following a public campaign in the 21st century, the British government issued an official apology in 2009, Queen Elizabeth II granted Turing a posthumous Royal Pardon in 2013, and his portrait now appears on the Bank of England's £50 banknote.