Like Zuse, Goldstine found help where he could—moonlighting telephone workers assisted with the wiring, Bell Labs supplied telephone parts and help with those parts, IBM designed a card reader for input and output. Goldstine, Mauchly, and Eckert seemed to work together quite well—Mauchly came up with the ideas but was considered by the others to be easily distracted. Eckert followed through, realizing the ideas in the machine and making sure that his designs were properly executed—he was noted for his perfectionism (and appreciated, in light of the expense and the danger of what he was putting together). Goldstine found the money, organized the personnel, and was the liaison with the army. He got along well with Eckert, but not well with Mauchly, who seemed like “a space case” to him. Eckert, it was clear to everyone, depended on Mauchly, but no one knew exactly why, even Mauchly. Since Mauchly was teaching at the same time, he wasn’t present at the building site as much as the others were. In 1944, when his teaching load was cut back so that he could work full time on ENIAC, his salary was cut from $5,800 to $3,900, leading to even more anxiety on his part. But he still felt that the project was his because he had originated it. It was at this point that he applied for a part-time job at the NOL, in the statistics department, and used Atanasoff as a reference. Atanasoff later said that he gave Mauchly a good recommendation more out of friendship than out of faith in his talents or expertise, but Mauchly got hired.
Mauchly mentioned his machine the first time in early 1944—according to Tammara Burton, “He looked Atanasoff in the eye and told him that he was building a new computer. The new computer, Mauchly claimed, isn’t ‘anything like your machine’; but is ‘better than your machine.’ ” When Atanasoff had asked about the new computer, Mauchly put him off, saying that it was top secret. Though Atanasoff’s security clearance was higher than Mauchly’s, Atanasoff knew he would not get anywhere by pressuring the other man. Atanasoff still believed at this point that Iowa State was likely to have filed the patent application. He knew that he himself would not have stolen another man’s ideas, so he didn’t suspect Mauchly—indeed, Mauchly assured him that the principles behind the ENIAC were entirely different from those behind the ABC. A few months later, in August 1944, Atanasoff met J. Presper Eckert for the first and only time, when Mauchly brought him to the gun factory in search of help with quartz transducers. Since Eckert did not have a high security clearance, the two men had to have a military escort, so the visit was brief and unrevealing. Although Atanasoff had agreed to help with the quartz transducers, he didn’t see Mauchly again. It was only later that it occurred to him that quartz transducers could be used in a computer to regenerate memory.
When it was completed, ENIAC was huge. It weighed twenty-seven tons, was eight feet long, eight feet high, and three feet deep. In addition to the 18,000 vacuum tubes, there were 7,200 diodes, 1,500 relays, 70,000 resistors, and 10,000 capacitors for memory storage. It required 150 kilowatts of power, the equivalent of 1,500 100-watt lightbulbs. Because of potential failure of the vacuum tubes, the machine was rarely turned off, but it did malfunction—Eckert said in 1989, “We had a tube fail about every two days and we could locate the problem within 15 minutes.” ENIAC was not a programmable computer—its switches had to be set and it had to be wired to perform its task; if the task changed, it had to be rewired and the switches reset. This could take weeks. The fact that ENIAC was not programmable was a by-product of the speed with which it was built. In his 1943 progress report, Brainerd rejected the added complexity such a feature would introduce—like Atanasoff, he didn’t want to fall into the trap Babbage had fallen into.
As the war progressed in Germany, Konrad Zuse continued to exercise his special genius, which was not just working hard on innovations to his machine, but also making and using all sorts of social connections to circumvent the increasing difficulties of finding materials and developing new ideas. As he began putting together the Z4, he cultivated acquaintances at the telephone exchange who had managed to avoid being drafted into the armed forces by making themselves appear more essential to the operation of German communications systems than they actually were. These “young, energetic, and enthusiastic” friends had access to junk bins, where over and over they turned up parts that Zuse could make use of. And Zuse’s own day job contributed to his understanding of what a computer might do—at one point, he devised a machine for Henschel that calculated optimum wing dimensions for innovative aircraft, a machine that worked fairly reliably for two years. This machine led to another machine designed to “mechanize dial gauge reading.” Although this machine was completed, Zuse had to abandon it almost as soon as he constructed it—he never learned whether it was blown up at the end of the war, or whether the Russian forces captured it. He writes, “Even as I was putting it together, the order came to dismantle the just-completed factory … But I went on working like a madman, driven solely by the ambition to see this interesting machine actually work at least once. Finally, it was created—the first process controlled computer. Even if not a single person had been interested, I had the pleasure of solving a difficult problem once again.”
Zuse and his colleagues began on the Z4 in 1942, building the machine in Berlin in the midst of air raids and fire bombings. On one occasion, Zuse was climbing the stairs in his office building and had just come to a landing when he heard “a crackling sound overhead.” As soon as he ducked into a nearby doorway, the staircase crumbled away. He managed to get down to the cellar and attempted to put out fires with a portable fire extinguisher, but the building burned to the ground anyway. All told, the Z4 had to be moved three times within the city limits of Berlin during the war. Even as Zuse persisted, he writes, “I didn’t always reach the cellar in time” to find safety—sometimes the air raid warnings would sound at just the time he was ready to test some function. But Zuse was dedicated—when he writes about building the Z4 during the war, he suggests that he was more fearful of the computer not functioning than he was of more mortal outcomes:
So, of course, when after weeks or months of work, I know that the time has come for the device to perform without a hitch, then the moment when the start button is to be pressed is especially tense. I always had a pronounced fear of such moments … It takes good nerves to withstand something like this for years on end.
Zuse was not entirely cut off from the outside world, but communication channels were idiosyncratic. At one point, Zuse’s bookkeeper told his own daughter about what Zuse was inventing. The daughter, who worked for German intelligence, responded by reporting that a similar machine was being developed in the United States. Zuse concocted the ruse of sending two assistants to the intelligence offices, where they presented what looked like an official document from the Air Ministry, asking to see the information. They were turned down, but since they had been told which drawer the photo was in, they managed to find it and bring it back to Zuse. The photo was of Howard Aiken’s Mark I. Zuse could not infer many technical details from the photo, but he became further convinced that computer development would have many, many applications in the postwar world. Unfortunately, in Germany, “hardly anyone could imagine commercial applications for our machines. Civilian production would also have been out of the question; it was officially forbidden.”
But Aiken’s Mark I, a machine that looked sleek and elegant (and huge) in the photograph Zuse saw, had a history in some ways as troubled as any of the other machines. Like most of the other scientists working on computers, Aiken joined the war effort (the Naval Reserve) once his PhD was completed. When IBM began building the Mark I (and, subsequently, Mark II–IV), IBM engineers began modifying Aiken’s design. The result was that Aiken became less and less involved with the final design features—the machine was taken over by the institutions that financed it. As the computer approached completion, IBM and Harvard made elaborate plans to unveil it in a joint ceremony. IBM, having spent half a million dollars ($6 million in 2010 dollars) building the machine, was eager to fully share the credit for it
s design and implementation. Aiken, however, seems to have done something—possibly contacting the press—that shifted the emphasis away from IBM and toward Harvard. Thomas J. Watson, Jr., later said, “If Aiken and my father had had revolvers they would both have been dead.” Hard feelings lingered for years afterward.
Alan Turing is now a famous man—the subject of biographies, papers, an opera, and at least one play, but his work at Bletchley Park breaking the Enigma code did not come to light until the 1970s, and then, at first, only by means of popular books that did not actually mention him, or mentioned him in cryptic ways (F. W. Winterbotham, The Ultra Secret, 1974; A. Cave Brown, Bodyguard of Lies, 1975), or in specialized publications that did mention him directly (Brian Randell, “On Alan Turing and the Origins of Digital Computers,” 1972; Brian Randell, editor, The Origins of Digital Computers: Selected Papers, 1973). Various accounts culminated in an episode about Turing and Enigma in a 1977 BBC series called The Secret War (other episodes concerned radio beams, radar, magnetic mines, and the V-1 and V-2, prototype German cruise missiles). Turing’s genius then captured the popular imagination, but so did his life, which was idiosyncratic, dramatic, and tragically short—he was not only a genius full of charming eccentricities and in some ways a paradigmatic Englishman, he was also an unashamed homosexual. Andrew Hodges, Oxford mathematician and gay activist, published his dense biography of Turing in 1983, which focused equally on Turing’s life and on his work. But there was much more going on at Bletchley Park between 1941 and 1944 than the cracking of the Enigma code.
The essential difference between Enigma messages communicated to German ships and Tunny messages was that Enigma messages were hand encoded, then communicated by radio broadcast, then hand decoded, while Tunny messages, also communicated by radio broadcast, were machine encoded and decoded, therefore not as subject to the human errors that allowed the English decoders to break the Enigma. The Tunny messages were also much more complex. The German army set up a radio network between Ukraine in the east, Brittany in the west, Tunis in the south, and Oslo in the north. Some stations were fixed, but most consisted of two equipment-carrying trucks, one with a sending Lorenz machine, a receiving Lorenz machine, and a teleprinter, the other with radio equipment.
Although in the early 1980s Tommy Flowers was given permission to describe the workings of the code-breaking machine named Colossus that he and his team of engineers built at top speed in 1943, he was forbidden to say what the machine had done or how it had been used in the war. It was only toward the very end of Flowers’s life, when the United States declassified some communications by American liaisons at Bletchley Park that mentioned Colossus and described its function, that the importance of the machines began to emerge (there were ten of them, the first Mark I that Flowers designed and built in 1943, and the nine Mark 2s that were larger and faster, built in 1944). In 2000, the British government finally declassified a long report on Colossus, written by code breakers in 1945, that revealed not only the complexity of Colossus but also its importance—and it was dramatically important.
The job of the Colossus team was the same as that of the Bombe builders—to infer by means of technical and theoretical deduction what the mechanical Lorenz encoding machines were doing and how they worked, and then to build a machine that mirrored that structure. In a teleprinter machine, upon which the Lorenz was based, a long strip of paper about an inch and a half wide passed through a slot the way a piece of paper passes over the roller of a typewriter, short end first. It was advanced by means of a line of tiny sprocket holes about three-fifths of the way between the left edge and the right edge. The pattern of holes standing for each letter of the alphabet and other essential characters according to the Baudot-Murray code, which had been invented by Emile Baudot in 1870, ran across the strip, three holes to the left of the sprocket holes and two holes to the right. The five positions in each row, some punched and some unpunched, represented a letter of the alphabet. For example, the letter M was represented as hole/hole/hole/no/no (or x x x . .) while the letter N was no/hole/hole/ no/no (or .x x . .). A message communicated by a normal teleprinter (or teletype machine, as it was called in the United States) consisted of a long blank strip of paper to indicate that a message was beginning, followed by a strip riddled with lines of holes, the length of which depended on the message, which was followed by another empty strip that indicated the end of the message. Since every letter consisted of five positions (hole or no), a six-letter word, such as “letter.” would consist of six lines. The words of the message ran down the strip: the word “colossus” would have looked like this:
Obviously, such a way of representing letters is time-consuming to generate by hand but easy by machine, easier than Morse code because the machine can punch an entire line at one time.
The job of the Lorenz machine was to take the principle of teletyping and encode the message so that it would be indecipherable except by the target Lorenz machine set to the same key as the originating machine. Since a teletype machine is based on the binary principle that a letter consists of five positions, some of which are punched (“1”) and some of which are not punched (“0”), then the machine used a binary arithmetical process to create the code. In Colossus, Jack Copeland calls this “the Tunny Addition Square” (appendix 3). The letters and symbols in the coded message were passed through the machine and “added” to letters in what was called the “keystream,” or the entirely different order of letters and symbols produced by the machine. The rules of addition were that 0 + 0 = 0, 1 + 1 = 0, 0 + 1 = 1, and 1 + 0 = 1 (note that this addition square is like Boolean algebra, but the values assigned to the results are specific to the rules of the Lorenz machine—it was not a mathematical machine and was not designed to solve math problems). The products of the addition of the coded letters to the keystream letters were systematic, and because the system was binary, if the Tunny receiving machine was set to the same keystream, all it had to do was take the coded message and add the letters and symbols of the keystream to the coded message, and the original message was retrieved. The Tunny Addition Square has 1,024 possible results (just like a base-ten multiplication table has 100 possible results). The more levels or “wheels” the machine employed, the more shifts were possible, and the German encoders employed the twelve wheels of the Lorenz machine in different ways, all of which were organized by headquarters. What the English eavesdroppers soon realized was that part of decoding the message was getting hold of the key (often transmitted between operators by hand) and using it to sift through the messages (transmitted by machine). However, what Turing understood was that with twelve different wheels, the number of possible variations was more enormous than human decoders could manage. Wheels 1–5 operated together (the code breakers called these the “psi” wheels after the second-to-last letter of the Greek alphabet). Wheels 8–12 also operated together (the “chi” wheels, after the third-to-last letter of the Greek alphabet). Wheels 6 and 7 were called the “motor” wheels. Each wheel had a number of positions—wheel 1 had forty-two positions, wheel 2 had forty-seven positions, for example. The job of the code breakers at Bletchley Park was to decipher the patterns in each set of teleprinted letters so that each shift of each wheel could be peeled away to reveal the original message. Intercepted encoded paper tapes were the raw material that Colossus had to process. Uncovering the shift pattern of one of the encoding wheels of the Lorenz machine was the key—once the position of the first wheel was ascertained, the positions of the next wheels became progressively easier to ascertain through Boolean logic. But while Enigma had three wheels, and then four, which was difficult enough, the Lorenz machine’s twelve wheels hugely enlarged the number of possibilities that had to be tested. And though sometimes with Enigma, the German operators encoding and sending the messages made mistakes that gave away the pattern, the mechanization of the Lorenz encoding process gave rise to fewer human errors, which was a large part of the reason Tunny was more difficult to decode.
In order to gain some idea of the work Colossus had to do, let’s imagine a message of five hundred holes and spaces representing one hundred letters (a very short message). It was the job of German intelligence officers to designate the positions and of the Lorenz operators to set the positions. Until the summer of 1944, the position of the psi wheels was set monthly and the chi wheels quarterly, then monthly. The motor wheels were set daily. As the war heated up in 1944, the positions of all the wheels changed daily.
The Dollis Hill communications research laboratories were located about eight miles northwest of central London, in an area that had originally been farms, then the estate of a politician who was a friend of William Gladstone and who had served as governor-general of Canada and lord lieutenant of Ireland. As close as it was to central London, the area retained its rustic feel into the twentieth century. But by the First World War, the team designing the Liberty tank, Mark VIII, was based there, and in 1921 the English government established the Post Office Research Station there. By 1933, a large brick factory and offices had been built, and at the beginning of World War II an underground bunker called Paddock was installed (though Churchill didn’t like it and wouldn’t stay there). The parts of the Colossus were shipped to Bletchley Park (about an hour’s drive farther northwest) and assembled there.