Mauchly’s memo was ignored by Penn’s deans, but it was brought to the attention of the Army officer attached to the university, Lieutenant (soon to be Captain) Herman Goldstine, a twenty-nine-year-old who had been a math professor at the University of Michigan. His mission was to speed up the production of firing tables, and he had dispatched his wife, Adele, also a mathematician, on a cross-country tour to recruit more women to join the battalions of human computers at Penn. Mauchly’s memo convinced him that there was a better way.
The decision of the U.S. War Department to fund the electronic computer came on April 9, 1943. Mauchly and Eckert stayed up all the night before working on their proposal, but they still hadn’t finished it by the time they got into the car for the two-hour ride from Penn to the Aberdeen Proving Ground in Maryland, where officials from the Ordnance Department were gathered. As Lieutenant Goldstine drove, they sat in the backseat writing the remaining sections, and when they arrived in Aberdeen, they continued working in a small room while Goldstine went to the review meeting. It was chaired by Oswald Veblen, the president of the Institute for Advanced Study in Princeton, who was advising the military on mathematical projects. Also present was Colonel Leslie Simon, director of the Army’s Ballistic Research Laboratory. Goldstine recalled what happened: “Veblen, after listening for a short while to my presentation and teetering on the back legs of his chair, brought the chair down with a crash, arose, and said, ‘Simon, give Goldstine the money.’ He thereupon left the room and the meeting ended on this happy note.”67
Mauchly and Eckert incorporated their memo into a paper they titled “Report on an Electronic Diff. Analyzer.” Using the abbreviation diff. was cagey; it stood for both differences, which reflected the digital nature of the proposed machine, and differential, which described the equations it would tackle. Soon it was given a more memorable name: ENIAC, the Electronic Numerical Integrator and Computer. Even though ENIAC was designed primarily for handling differential equations, which were key to calculating missile trajectories, Mauchly wrote that it could have a “programming device” that would allow it to do other tasks, thus making it more of a general-purpose computer.68
In June 1943 construction of ENIAC began. Mauchly, who retained his teaching duties, served as a consultant and visionary. Goldstine, as the Army’s representative, oversaw the operations and budget. And Eckert, with his passion for detail and perfection, was the chief engineer. Eckert became so dedicated to the project that he would sometimes sleep next to the machine. Once, as a joke, two engineers picked up his cot and gently moved him to an identical room one floor up; when he awoke he briefly feared the machine had been stolen.69
Knowing that great conceptions are worth little without precision execution (a lesson Atanasoff learned), Eckert was not shy about micromanaging. He would hover over the other engineers and tell them where to solder a joint or twist a wire. “I took every engineer’s work and checked every calculation of every resistor in the machine to make sure that it was done correctly,” he asserted. He disdained anyone who dismissed an issue as trivial. “Life is made up of a whole concentration of trivial matters,” he once said. “Certainly a computer is nothing but a huge concentration of trivial matters.”70
Eckert and Mauchly served as counterbalances for each other, which made them typical of so many digital-age leadership duos. Eckert drove people with a passion for precision; Mauchly tended to calm them and make them feel loved. “He was always kidding and joking with people,” Eckert recalled. “He was personable.” Eckert, whose technical skills came with a nervous energy and scattershot attention span, badly needed an intellectual sounding board, and Mauchly loved being that. Although he was not an engineer, Mauchly did have the ability to connect scientific theories with engineering practicalities in a way that was inspiring. “We got together and did this thing and I don’t think either of us would have done it by ourselves,” Eckert later conceded.71
ENIAC was digital, but instead of a binary system, using just 0s and 1s, it used a decimal system of ten-digit counters. In that regard, it was not like a modern computer. Other than that, it was more advanced than the machines built by Atanasoff, Zuse, Aiken, and Stibitz. Using what was called conditional branching (a capability described by Ada Lovelace a century earlier), it could hop around in a program based on its interim results, and it could repeat blocks of code, known as subroutines, that performed common tasks. “We had the ability to have subroutines and subroutines of subroutines,” Eckert explained. When Mauchly proposed this functionality, Eckert recalled, “it was an idea that I instantly recognized as the key to this whole thing.”72
After a year of building, around the time of D-Day in June 1944, Mauchly and Eckert were able to test the first two components, amounting to about one-sixth of the planned machine. They started with a simple multiplication problem. When it produced the correct answer, they let out a shout. But it took more than another year, until November 1945, for ENIAC to be fully operational. At that point it was able to perform five thousand additions and subtractions in one second, which was more than a hundred times faster than any previous machine. A hundred feet long and eight feet high, filling the space of what could be a modest three-bedroom apartment, it weighed close to thirty tons and had 17,468 vacuum tubes. By contrast, the Atanasoff-Berry computer, then languishing in a basement in Iowa, was the size of a desk, had only three hundred tubes, and could do merely thirty additions or subtractions per second.
BLETCHLEY PARK
Although few outsiders knew it at the time—and would not know for more than three decades—another electronic computer using vacuum tubes had been secretly built at the end of 1943 on the grounds of a redbrick Victorian manor in the town of Bletchley, fifty-four miles northwest of London, where the British had sequestered a team of geniuses and engineers to break the German wartime codes. The computer, known as Colossus, was the first all-electronic, partially programmable computer. Because it was geared for a special task, it was not a general-purpose or “Turing-complete” computer, but it did have Alan Turing’s personal fingerprints on it.
Turing had begun to focus on codes and cryptology in the fall of 1936, when he arrived at Princeton just after writing “On Computable Numbers.” He explained his interest in a letter to his mother that October:
I have just discovered a possible application of the kind of thing I am working on at present. It answers the question “What is the most general kind of code or cipher possible,” and at the same time (rather naturally) enables me to construct a lot of particular and interesting codes. One of them is pretty well impossible to decode without the key, and very quick to encode. I expect I could sell them to H.M. Government for quite a substantial sum, but am rather doubtful about the morality of such things. What do you think?73
Over the ensuing year, as he worried about the possibility of war with Germany, Turing got more interested in cryptology and less interested in trying to make money from it. Working in the machine shop of Princeton’s physics building in late 1937, he constructed the first stages of a coding machine that turned letters into binary numbers and, using electromechanical relay switches, multiplied the resulting numerically encoded message by a huge secret number, making it almost impossible to decrypt.