Shannon’s cryptography work had one other lasting import: it brought him into contact with another giant of the digital age, Alan Turing. In 1942, Turing came to America as a part of a government-initiated tour of military encryption projects. By this point, his reputation preceded him. He had demonstrated astonishing mathematical precocity in primary school; mastered Einstein’s work by sixteen; and by twenty-three had been elected a fellow of King’s College, Cambridge. In 1936, he dreamed up the Turing Machine, a landmark thought experiment that served as the theoretical underpinning of the modern computer.
Turing had also begun the codebreaking that would make him a world-historic figure. It was cryptography that had brought him to the United States, on orders to connect with American counterparts, meet the military leaders in the space, and inspect the American machinery for quality and security. This extended to, among other projects, SIGSALY; if British leaders were to be on the receiving end of its buzzing, Dr. Turing would have to give his stamp of approval that the system was unbreakable.
The secrecy of the subject matter, the reputations of Turing and Shannon, and the atmosphere of the war has lent this meeting of the minds an air of intrigue and mystery. But there was nothing cloak-and-dagger about their interactions. According to Turing’s biographer, Andrew Hodges, Shannon and Turing met daily over tea, in public, in the conspicuously modest Bell Labs cafeteria. Turing was envious, in a way, of Shannon’s multifaceted career: “Here [Turing] met a person who had been able to take the part of an academic, philosophical engineer, the role that Alan might have liked had the English system allowed for it.” Shannon, for his part, was amazed by the quality of Turing’s thinking. “I think Turing had a great mind, a very great mind,” Shannon later said.
Neither left a record of their conversations, but we do know the one topic they avoided. “We talked not at all about cryptography. . . . I don’t think we exchanged word one about cryptography,” Shannon explained. Asked whether or not he knew what Turing was working on, Shannon responded that he only knew it in broad strokes. “Certainly not the nitty gritty. I knew or surmised what he was doing. . . . I had no concept of the Enigma machine. . . . I didn’t know of that nor that he was a crucial figure in it.” The interviewer pressed him, asking him why Shannon, with his own passion for and experience in cryptographic puzzles, wouldn’t have probed Turing further. Shannon’s response was simple and to the point: “Well, in the wartime you didn’t ask too many questions.”
To some, Shannon and Turing’s professed ignorance of the other’s work might seem like a pair of codebreakers smartly covering the tracks of their relationship. But it’s entirely plausible that neither man wished to put the other in an uncomfortable or compromised position. The work on both sides was highly classified. The information they had each been given was, if not for their eyes only, certainly for those of a limited audience. It’s no surprise that, given a break from their labors over tea and cake, the two men would spend time talking about anything other than the work that occupied their days.
Another reason: questions about how much the Americans were willing to share with the British were still up in the air. Even for someone of Turing’s stature and reputation, obtaining the relevant clearances for his American trip had been an ordeal. He had, amazingly enough, been detained by the American authorities on arrival: “I reached New York on Friday November 12th. I was all but kept on Ellis Island by the Immigration Authorities who were very snooty about my carrying no orders and no evidence to connect me with the F.O. [Foreign Office].”
Months earlier, the American general Rex Minckler had rejected Turing’s application to enter Bell Laboratories. Though the application was, at length, finally approved, it only marked the beginning of a protracted tussle with the Bell Labs and national security bureaucracies. Turing wrote:
I had been intending to report to Potter at Bell Laboratories without any more formality than a preliminary phone call. This was apparently all wrong. . . . There was some trouble because no arrangements for me to see anything other than unscrambling projects had been confirmed in writing, whereas I had come out on the understanding that I was to see everything there was in the way of speech secrecy work. . . . [I] immediately came up against a veto on any British people visiting anything at all in the speech scrambling line. Captain Hastings then took a hand, and brought the pressure to bear on General Colton, and all now seems to be well.
Turing wasn’t alone in his aggravation with the Americans, nor did that frustration limit itself to immigration and security clearance snafus. Though the Allied forces had been working together in the war effort since the Lend-Lease Act, they didn’t always see eye to eye on cryptographic matters.
Competing systems, methods, and personalities left the two sides perpetually suspicious of one another; tempers ran short, and egos bruised easily. The conflict was due, in part, to essential differences between the American and British war machines, and to their “incomplete alliance.” For all their ramp-up in industrial production of military goods, the British simply could not keep pace with the Americans in scale or speed. Turing saw this firsthand, and his respect for American brains was, in some ways, the inverse of his respect for American brawn. After a visit to the Navy Department, for instance, he wrote: “I am persuaded that one cannot very well trust these people where a matter of judgment in cryptography is concerned.” Still, “I think we can make quite a lot of use of their machinery.”
That attitude of qualified mistrust was common on both sides. Certain British successes in codebreaking, for instance, were kept hidden from the Americans, and Turing did not have a clear sense of what he was and was not allowed to share with his hosts. Already known for his brusque, off-putting manner, Turing wasn’t going to ingratiate himself with the Americans when the very purpose of his mission was so clouded with uncertainty, nor was he the kind of natural diplomat capable of finessing the problem.
But in a way, the bad feelings between the two sides, and the muzzles placed on both Shannon and Turing, freed the pair to talk about their other common interests. A friendship blossomed where only a modest professional relationship might have sprung up had they been freer to talk about cryptographic matters. Even before the war years, both Turing and Shannon had shared similar extracurricular enthusiasms, and both had been dancing around the same set of cutting-edge ideas. Over their cups of tea, remembered Shannon, “we would talk about mathematical subjects.” In particular, thinking machines were much on the two men’s minds—in Shannon’s words, “the notion of building computers that will think and what you can do with computers and all that.” He went on:
Turing and I had an awful lot in common, and we would talk about that kind of question. He had already written his famous paper about Turing Machines, so called, as they call them now, Turing Machines. They didn’t call them that then. And we spent much time discussing the concepts of what’s in the human brain. How the brain is built, how it works and what can be done with machines and whether you can do anything with machines that you can do with the human brain and so on. And that kind of thing. And I had talked to him several times about my notions on Information Theory, I know, and he was interested in those.
They were, both, taken by the promise of early computing and intrigued by the idea of chess-playing computers. Here’s Shannon in 1977:
Well, back in ’42 . . . computers were just emerging, so to speak. They had things like the ENIAC down at University of Pennsylvania. . . . Now they were slow, they were very cumbersome and huge and all, there were computers that would fill a couple rooms this size and they would have about the ability of one of the little calculators that you can buy now for $10. But nevertheless we could see the potential of this, the thing that happened here if things ever got cheaper and we could ever make the uptime better, sort of keep the machines working for more than ten minutes, things like that. It was really very exciting.
We had dreams, Turing and I used to talk about the possibility of simulating entirely the human brain, could we really get a computer which would be the equivalent of the human brain or even a lot better? And it seemed easier then than it does now maybe. We both thought that this should be possible in not very long, in ten or 15 years. Such was not the case, it hasn’t been done in thirty years.
At his core, Shannon was a private person, with fewer confidants than his stature within the scientific community might suggest. In a life of exposure to many of the world’s leading scientists, mathematicians, and thinkers, Shannon always gave the impression of a wallflower, someone who may have found himself in the same conference halls as many of the luminaries of his day but generally waited for the conversation to come to him. He wasn’t a steady correspondent with the major figures he knew, attended only a fraction of the conferences to which he was invited, and was the sort of person for whom the concept of “networking” was distasteful when applied to anything other than telephone lines. All of which is to say that the fact he connected as enthusiastically as he did with Turing is as remarkable as anything the pair discussed. That Shannon could, in the brief few months they had together at Bell Labs, win Turing’s confidence and friendship says a great deal about each man’s high opinion of the other. Turing was, in Shannon’s words, “a very, very impressive guy.” Turing even visited Shannon at home, a rarity for a host who so preferred his own company—and a guest who did, too.
After Turing’s return to Great Britain, he and Shannon met one final time, in the war’s aftermath. In 1950, Claude traveled to London for a conference and took time to visit Turing and his laboratory. As Shannon remembered:
While there we went over to Turing’s Laboratory in Manchester at the University of Manchester. . . . He was interested in programming a computer for chess, which . . . was a problem that had interested me a great deal. And he was working away with programming a computer at this time. And he had an office up there, and there was a computer downstairs. This was in the early days of computers.
The two discussed Turing’s efforts at programming. Even decades later, Shannon would recall one of Turing’s inventions:
So I asked him what he was doing. And he said he was trying to find a way to get better feedback from a computer so he would know what was going on inside the computer. And he’d invented this wonderful command. See, in those days they were working with individual commands. And the idea was to discover good commands.
And I said, what is the command? And he said, the command is put a pulse to the hooter, put a pulse to the hooter. Now let me translate that. A hooter . . . in England is a loudspeaker. And by putting a pulse to it, it would just be put a pulse to a hooter.
Now what good is this crazy command? Well, the good of this command is that if you’re in a loop you can have this command in that loop and every time it goes around the loop it will put a pulse in and you will hear a frequency equal to how long it takes to go around that loop. And then you can put another one in some bigger loop and so on. And so you’ll hear all of this coming on and you’ll hear this “boo boo boo boo boo boo,” and his concept was that you would soon learn to listen to that and know whether when it got hung up in a loop or something else or what it was doing all this time, which he’d never been able to tell before.
It was an altogether enjoyable visit, a postwar reunion for two of the founders of the Information Age. It was also the last time that they would speak in person. Four years after Shannon’s visit, Turing—following a conviction for “gross indecency” at a time when homosexuality was criminalized—died of cyanide poisoning. His death was ruled a suicide, though its circumstances remain in dispute to this day.