- Historic Sites
In a top-secret program, talented, young female mathematicians calculated the artillery and bomb trajectories that American GIs used to win World War II
Fall 2011 | Volume 61, Issue 2
By June 1945, Mauchly and Eckert were ready to get ENIAC up and running, and they turned to the computing Rosies to help operate or, as it would soon be known, "program" the machine. Betty Jean Jennings, a math major from rural Missouri who had joined the PCS that spring, attended a meeting for potential programmers. "They didn't know what to ask us, basically," she said. "I remember Herman [Goldstine] asking me what I knew about electricity. I said I had had a course in physics and knew E = I/R. He replied what he really wanted to know was, 'Are you afraid of it?' I replied that I wasn't." Six women—Jennings, Kathleen (Kay) McNulty, Frances Bilas, Elizabeth (Betty) Snyder, Ruth Lichterman, and Marlyn Wescoff—from the PCS were selected to join the ENIAC project and went to Aberdeen for several weeks of training.
Although they had already been doing secret work with the PCS, they weren't even permitted to see the finished machine until the government had approved higher security clearances for them. Frantic preparations were under way for the computer's public unveiling, but in the meantime it remained top secret. Kay McNulty remembered, "Somebody gave us a whole stack of blueprints, and these were the wiring diagrams for all the panels, and they said, 'Here, figure out how the machine works and then figure out how to program it.' This was a little bit hard to do." They studied the intricate circuitry, wiring, logic, and operation of ENIAC, a 27-ton behemoth with almost 18,000 vacuum tubes, thousands of other parts, and miles of wiring.
After finally meeting Mauchly, they fired questions at him as they worked to develop the computer's programming. "Occasionally, the six of us programmers all got together to discuss how we thought the machine worked," Jennings recalled. "The biggest advantage of learning the ENIAC from the diagrams was that we began to understand what it could and could not do. As a result we could diagnose troubles almost down to the individual vacuum tube. Since we knew both the application and the machine, we learned to diagnose troubles as well as, if not better than, the engineer.
By the fall they were preparing a demonstration program on how to compute a shell trajectory. Before that happened, however, two scientists arrived from Los Alamos to give ENIAC its first real-world problem to solve. Theoretical work on the hydrogen bomb had been under way at the lab for some time and continued after Japan's surrender. In October 1945 Stanley Frankel and Nicholas Metropolis decided to use ENIAC to explore how an atomic bomb could trigger a thermonuclear reaction.
It was all top secret, of course, and Frankel and Metropolis brought their own program with them to Philadelphia on a million IBM punch cards. But the women were essential to running the program and operating the machine. "The day we were going to put it on the machine is the first time we saw the ENIAC," Jennings recalled. "Herman Goldstine acted like the conductor of an orchestra and stood in the middle and said, 'Accumulator 1, Switch 1, set to Alpha Input,' you know, 'blah, blah,' and he was reading from their description. That was our first hands-on experience with the machine."
ENIAC was set to be revealed to the public in February 1946. "About two weeks before the public announcement of ENIAC," remembered Jennings, "Herman and Adele Goldstine asked us if our trajectory program was ready to go. We said it was. They asked if we could have it up and running for the demonstration at the announcement. We said it could." The program, however, hadn't actually been tested, and although Jennings and her partner, Betty Snyder, were fully confident, no one could be sure until ENIAC had been taken through its paces.
The women worked days, nights, and weekends to get ready. John Mauchly shared a bottle of apricot liqueur with the programmers to wish them luck. Then, the night before the public demonstration, they hit a snag. "The trajectory program was running perfectly, except it didn't stop computing when [the shell] was calculated to hit the ground," Jennings said. "It kept going. Betty and I checked and rechecked everything until about 2 a.m. We couldn't figure out what on earth was going on."
She credited Snyder with finding the answer. "I've always said that Betty uses more logic in her sleep than most people do awake. We used to have a problem and she'd come in the next morning and say, 'I was thinking, you know, maybe this,' and usually she was right. Well, that night she had her nighttime logic working. She came in the next morning and flipped one switch on the master programmer and the problem was solved." ENIAC's coming-out party before scientists and the press proved a huge success.
The women, however, soon found themselves shunted aside from sharing in that success. "You can see them being dismissed almost immediately," noted historian Nathan Ensmenger of the University of Pennsylvania. "They have a dinner in which they ask all the university bigwigs and military people and all of the men, and none of the women are invited." Historian Jennifer Light of Northwestern University concurred: "Newspaper accounts characterize ENIAC's ability to perform tasks as 'intelligent,' but the women doing the same computing tasks did not receive similar acclaim." A New York Times account of the demonstration marveled at how ENIAC solved a difficult problem in 15 seconds, she pointed out, while ignoring the many hours that the women spent setting up the problem on the machine.