In 1945, Betty “Jean” Jennings wanted out of Missouri. A math student at Northwest Missouri State Teachers College (now Northwest Missouri State University), the last thing the farm-bred 20-year-old wanted to do was stay inside a classroom and teach. She wanted adventure. So when an advisor showed her a mysterious classified ad in a math journal soliciting mathematicians to come work in Pennsylvania, Jean jumped at the chance.

She applied for the job, was accepted, and hopped the next steam locomotive to Philadelphia. Little did she know that her leap of faith would help launch the modern computer. Although she and the women like her would be all but forgotten, Jean Jennings’s pioneering work helped create the technology that made the information age buzz.

Uncovering the Women Behind ENIAC

In the mid-1980s, Kathy Kleiman felt isolated and discouraged. A computer science undergrad at Harvard, she began noticing a dramatic drop-off in the number of women in her classes as the course level went up. It was not an auspicious sign for her future in programming.

“I found myself wondering if women had much of a role in the history of computing at all,” Kleiman says. “So I turned to history to see if I could find any role models.”

UPenn

In her research she stumbled upon a famous black-and-white photo of the first all-electric computer. Published in major newspapers across the country in 1946, the caption identified the men in the image, but no one else. Kleiman was perplexed. Why were the men in the photo the only ones identified? Who were the women?

She took her questions to a historian of computing, but it turned out no one knew who the women were. “I was told they were models—‘Refrigerator Ladies’—posing in front of the machine to make it look good,” Kleiman says. This was a common marketing tactic used to sell kitchen appliances like refrigerators at the time. “But they didn’t look like models to me. In fact, that was the farthest thing from the truth.”

The Birth of the Electric Computer

In World War II the Army was tasked with a Herculean job: calculate the trajectories of ballistic missiles—the arcs that artillery shells take from the time they leave cannon muzzles to the time they reach their target—by hand. These differential calculus equations (a PDF of those calculations can be seen here) were used to target the weapons, and as the firepower increased in the field, so did the demand for the ballistics firing tables. The problem was that each equation took 30 hours to complete, and the Army needed thousands of them.

So they started recruiting every mathematician they could find. They placed ads in newspapers, first in Philadelphia, then in New York City, then far out west in places like Missouri, seeking women “computers” who could hand-compute the equations using mechanical desktop calculators. They would need to relocate to the University of Pennsylvania.

“If they could calculate a differential calculus equation, they were hired,” Kleiman says. Male mathematicians were already working on other projects, so the Army specifically recruited women, even hiring ones who hadn’t graduated college yet. “Like everything else during early WWII, where they needed lots of people, like in factories and farms, they hired women,” she says. At the height of the program, the Army employed more than 100 women calculators. One of the last women to join the team was a farm girl named Jean Jennings.

But the calculations weren’t coming out fast enough, so the Army funded an experimental project to automate the trajectory calculations. Engineers John Presper Eckert and John W. Mauchly began designing the Electronic Numerical Integrator and Computer, or ENIAC as it was called.

“Few in the Army thought the highly-experimental ENIAC would work, but the need was great and it was a time to experiment,” Kleiman says. That experimenting paid off: The 80-foot long, 8-foot tall, black metal behemoth, which contained hundreds of wires, 18,000 vacuum tubes, 40 8-foot cables, and 3000 switches, would become the first all-electric computer.

Making it Work

When the ENIAC was nearing completion in the spring of 1945, the Army randomly selected five women computers out of the 100 or so workers (later adding a sixth woman to the team) and tasked them with programming the thing. “The engineers handed the women the logistical diagrams of ENIAC’s 40 panels and and the women learned from there," Kleiman says. "They had no programming languages or compilers. Their job was to program ENIAC to perform the firing table equations they knew so well.”

The six women—Francis “Betty” Snyder Holberton, Betty “Jean” Jennings Bartik, Kathleen McNulty Mauchly Antonelli, Marlyn Wescoff Meltzer, Ruth Lichterman Teitelbaum, and Frances Bilas Spence—had no precedent and only schematics to work with.

“There was no language, no operating system, no anything,” Kleiman says. “The women had to figure out what the computer was, how to interface with it, and then break down a complicated mathematical problem into very small steps that the ENIAC could then perform.” They physically hand-wired the machine, an arduous task using switches, cables, and digit trays to route data and program pulses.

“The ENIAC was a son of a bitch to program,” Jean Jennings has said.

The ballistic calculations went from taking 30 hours to complete by hand to taking mere seconds to complete on the ENIAC.

On February 14, 1946, six months after the end of the war, the Army revealed their amazing feat of engineering in a public relations extravaganza. (The ENIAC was not completed in time to use during World War II.) ENIAC was front-page news across the country, a milestone in modern computing, with praise going to the military, the Moore School of Electrical Engineering at the University of Pennsylvania, and Eckert and Mauchly, the hardware engineers. The programmers, all women, were not introduced at the event. And even though some of them appeared in photographs at the time, everyone assumed they were just models.

After the war, the government ran a campaign asking women to leave their jobs at the factories and the farms so returning soldiers could have their old jobs back. Most women did, leaving careers in the 1940s and 1950s and staying at home. But no returning soldier knew how to program the ENIAC.

“We were like fighter pilots,” programmer Kathleen McNulty has said. “You couldn’t just take any ordinary pilot and stick him into a fighter [jet] and say, ‘Go to it now, man.’ That was not the way it was going to be.”

“The Army didn’t want to let this group of women go,” Kleiman says. “All of these women had gone to college at a time when most men in this country didn’t even go to college. So the Army strongly encouraged them to stay, and for the most part, they did, becoming the first professional programmers, the first teachers of modern programming, and the inventors of tools that paved the way for modern software.”

The Army opened the ENIAC up to perform other types of non-military calculations after the war and Betty Holberton and Jean Jennings converted it to a stored-program machine. Betty went on to invent the first sort routine and help design the first commercial computers, the UNIVAC and the BINAC, alongside Jean.

Setting History Straight

In the 1990s Kleiman learned that most of the ENIAC programmers were not invited to the ENIAC’s 50th anniversary event. So she made it her mission to track them down and record their oral histories. Today, Kleiman, an Internet lawyer, is putting the finishing touches on her documentary and book on the six ENIAC programmers. The documentary, intended to inspire young women and men to get involved in programming, is set to be released in the coming months.

“They were shocked to be discovered,” Kleiman says. “They were thrilled to be recognized, but had mixed impressions about how they felt about being ignored for so long.”

Jean Jennings, the last surviving programmer from the original six, passed away on March 23, 2011 at 86. Northwest Missouri State University, her alma mater, named its computing museum in her honor.