I work across mathematics, logic, cryptanalysis, computer design and theoretical biology. My best-known contribution is the Turing machine, a formal model of algorithm and computation that can stand in for a general-purpose computer.
In "The Chemical Basis of Morphogenesis" (January 1952) — research in mathematical biology — I proposed that chemicals reacting and diffusing at different rates, an activator and an inhibitor, can account for the main phenomena of biological pattern formation.
In "Computing Machinery and Intelligence" I replaced the question of whether machines can think with an experiment: if a human interrogator cannot tell a computer from a human through conversation, it can be said to think — a founding question for computer science and research on machine intelligence.
As deputy director of the Computing Machine Laboratory at Manchester, I worked on programming and software for one of the earliest stored-program computers, wrote the first Programmer's Manual for the Mark 1, and consulted for Ferranti on the Ferranti Mark 1.
At the National Physical Laboratory I designed the ACE (Automatic Computing Engine) and presented it on 19 February 1946 — the first detailed design of a stored-program computer, where program and software sit in the same memory as data. The Pilot ACE ran its first program on 10 May 1950.
After working with Bell Labs on secure speech technology, I designed and built Delilah with REME officer Donald Bayley — a portable voice-encryption machine, a piece of electronic engineering I demonstrated by encrypting and decrypting a recording of a Churchill speech.
In July 1942 I devised Turingery, a codebreaking procedure for working out the cam settings of the wheels of the German Lorenz SZ 40/42 teleprinter cipher, codenamed Tunny at Bletchley Park — research that fed the engineering of Colossus.
In October 1941, with Welchman, Alexander and Milner-Barry, I wrote directly to Winston Churchill — as first named — after proper channels failed to fund staff and bombes. He ordered our needs met on extreme priority.
I took on German naval Enigma, whose indicator system was more complex than the other services'. In December 1939 I solved its essential part, and that same night conceived Banburismus to cut the bombe time needed to test settings.
My own explanation for choosing the hardest open problem at Bletchley Park — German naval Enigma — and my candid admission that I was not sure Banburismus would work until it had actually broken days.
For Banburismus I invented the ban, a measure of weight of evidence, and accumulated it sequentially until it was sufficient to decide — the procedure Abraham Wald later called sequential analysis, now a standard tool of statistical science and research.
The bombe is an engineering answer to a search problem: the machine searches Enigma's rotor order, rotor settings and plugboard settings by chaining logical deductions from a crib and discarding every setting that produces a contradiction, leaving only a few for hand checking.
With Dilly Knox I developed a crib-based approach to Enigma that did not depend on the German indicator procedure, and I wrote the engineering specification of the bombe — the machine design behind the codebreaking technology. The first one was installed on 18 March 1940.
