The black-and-white photos showed smartly dressed women deftly configuring wires on an enormous machine—the first general-purpose all-electronic digital computer. When Kathy Kleiman, a computer programmer and historian, came across these pictures, it was clear to her that these young women knew what they were doing.

“I had been told they were models,” she says. “And of course, they’re not.”

Those women, Kleiman discovered, were the first modern computer coders, or programmers, in the U.S. The two men who had designed the computer, called the ENIAC, had been well-known since 1946. Yet for decades, computer historians had no idea who the women in those photos were, and simply assumed that they had nothing to do with the groundbreaking machine. By the time the six female programmers finally received public recognition, most were in their 70s.

These six women developed the new field of computer programming during World War II, a time when the government was encouraging women to take on wartime jobs while male soldiers fought overseas. Originally, the military had hired them as “computers” to calculate ballistics trajectories by hand. This meant determining the angle soldiers should fire at based on how far away the target was, what the weather conditions were that day, and other factors. By 1945, they were part of nearly 100 female mathematicians working as “computers.”

Calculating these trajectories by hand took a really, really long time, and two male engineers—John Mauchly and J. Presper Eckert—thought they could design a special machine that would calculate them faster. They called the new machine the ENIAC, or Electronic Numerical Integrator And Computer, and hired six of the female “computers” to perform calculations with it.

The team included Jean Jennings Bartik, who would later lead the development of computer storage and memory, and Frances Elizabeth “Betty” Holberton, who would go on to create the first software application. Together with Frances Bilas Spence, Marlyn Wescoff Meltzer, Kathleen “Kay” McNulty Mauchly Antonelli, and Ruth Lichterman Teitelbaum, they laid the groundwork for future programmers and software engineers. And, since they were the first modern coders, they were instrumental in teaching others to program after the war.

In the beginning, they weren’t even allowed into the ENIAC room because they didn’t yet have the security clearance. Instead, they were expected to code the machine using only paper diagrams of it. These diagrams didn’t come with any instructions—they had to figure it out themselves without any programming languages or manuals, because none existed.

But while the male inventors of the ENIAC received awards and publicity, these women received no recognition for their pioneering efforts. On the ENIAC’s public debut on February 14, 1946, Mauchly and Eckert were introduced to the press as the ENIAC’s designers. The women were never introduced, and they weren’t invited to the Army dinner celebrating the debut either. When their pictures appeared in the press, the captions didn’t even mention their names or roles. Because they were women, it was assumed that the work they did must not have been very difficult.

“In the beginning, there was a general sense that the computer itself was doing the work, and building the computer was the really important thing,” says Janet Abbate, a professor of science and technology in society at Virginia Tech and author of Recoding Gender. “It took a few decades to really get to the point now, where we just take for granted that software is important.”

Programming the ENIAC was an intellectually demanding job that involved extensive preparation, planning, learning about the ENIAC from its logical diagrams, and then configuring wires on a massive machine stretching across a 50-by-30-foot room. Or, as Bartik put it in the documentary The Computers, “the ENIAC was a son of a bitch to program.”

Although women who performed other wartime jobs had always been expected to give the jobs up to men when they returned from the war, this wasn’t the case with programming. After all, men had never done it before.

“The Army did not kick these six women out,” says Kleiman, who produced The Computers as part of her ENIAC Programmers Project. “Because no one else had programmed this thing. No soldier returning from the war had the skill set these women did.”

New women began to enter the field, too. “After the war there was such a boom in computing that there were more jobs than qualified people to fill them,” Abbate says. “And so that was another reason why women weren’t pushed out, they were pulled in.”

Although the boom pulled in more men than women, the percentages of women in programming were much higher than those in other STEM fields. Still, even with the introduction of men, programming was often conflated with low-level clerical work commonly performed by women like typing or filing, writes Nathan Ensmenger, a professor of informatics and computing at Indiana University.

These stereotypes about the job helped keep its pay and prestige low. Yet programmer Grace Hopper, who invented the first computer language compiler (which transferred mathematical code into machine code), also used gender stereotypes to encourage women to enter the field. In a 1967 Cosmopolitan article titled “The Computer Girls,” she quipped that programming is “just like planning a dinner.” Hopper continued: “Programming requires patience and the ability to handle detail. Women are ‘naturals’ at computer programming.”

“People like Grace Hopper were very consciously mobilizing gender stereotypes to get women in,” Abbate says. Programming, some argued, was similar to knitting, sewing, or even crossword puzzles, so women were a perfect fit.

Over time, stereotypes about the field shifted to the point that computer programming came to be seen as a job better suited for men than women. Instead of a job that was perfect for detail-oriented women who loved to collaborate and plan, it became a job for antisocial, “geeky” boys. In the summer of 2017, a white male programmer at Google was fired for writing widely-circulated memo that used gender stereotypes to argue that women were inherently worse at programming than men.

There are multiple likely factors that contributed to programming’s shift from a women-friendly occupation to one that is hostile to women. In the 1950s and ‘60s, employers began relying on aptitude tests and personality profiles that weeded out women by prioritizing stereotypically masculine traits and, increasingly, antisocialness. Abbate says the 1970s recession might have also caused a drop-off in the number of women entering the field, because it was the first time programmers weren’t so in-demand.

In addition, Jane Margolis, a senior researcher at the University of California-Los Angeles and author of Unlocking the Clubhouse, cites the introduction of the home computer as a “boy's toy” in the 1980s as a factor that pushed more men than women into computer science. Radio Shack ran ads showing that personal computers were great for nerdy (white) boys and sporty boys because they could use it to do homework and play video games. Another 1985 Apple ad showed how much a computer could help a boy named Brian Scott, while also demonstrating what fun he could have teasing a girl who was trying to use a computer.

When professions shift from male-dominated to female-dominated, they usually see decreases in pay and prestige. Teaching and nursing, once considered male fields, are today largely low-paying, pink-collar occupations. In the case of computer programming, this transformation ran in reverse. Although it’s not clear exactly how much programmers earned in the ‘40s and ‘50s, it definitely wasn’t comparable to Google’s $106,900 “early career median pay” of today. Women could be promoted to other technical jobs, but could not advance into “big-money sales and management jobs,” Abbate says. By 1969, the median salary for female computer specialists was $7,763, Abbate writes in Recoding Gender. In contrast, men earned a median of $11,193 as computer specialists and $13,149 as engineers.

These underpaid, undervalued women who played such a critical role in developing their field might never have gotten their due at all without the work of female historians like Kleiman and Abbate. Margot Lee Shetterly’s book Hidden Figures and its 2017 film adaptation helped fill in some gaps in the historical record regarding influential black female mathematicians—including Dorothy Vaughan, an expert in the FORTRAN programing language.

There are likely many more “hidden figures” whose contributions have yet to be found. Finding these women isn’t just important because it gives credit where credit is due. It also counters narratives that women don’t have a place in modern programming.

“This is not a field women are newcomers to,” Abbate says. “This is a field where they have a history and belong.”