What Turing had already built

By 1950, Turing was not an unknown theorist with an interesting idea.

During the Second World War, at , he became one of the central figures in breaking , the encryption system used by Nazi Germany. The work is widely credited with shortening the war.

Before that, while still in his twenties, he had invented something more abstract: a theoretical model now called the , which could describe the limits of what any computer could ever do. It was only a thought experiment. It became one of the foundations of modern computing.

He was not someone who thought carefully about machines from a distance. He had built them, debugged them, and trusted their outputs with lives.