When the world's first computer, ENIAC, debuted in 1946, nobody mentioned that six women had programmed it. Nor did most people realize that female coders worked behind the scenes on many of its successors. One of them was a Yale-educated math whiz named Grace Hopper, who pioneered user-friendly computer languages and was a lead programmer on the Universal Automatic Computer (UNIVAC). Her work underpinned countless technological advancements, like the data processing for the 1950 U.S. Census. That same 1950 census data Hopper helped digitize is getting its own pioneering advancement via AI handwriting recognition technology developed by Ancestry®.

Hopper was among the many trailblazing women in technology whose achievements are still with us today. In the middle of the 20th century, women were star codebreakers, programmers, mathematicians, and scientists, but their importance has only recently come to light. Here's how they made history by breaking the mold and “rewriting the code” of their time.

Opportunities for Women Expanded in the 1940s

Few jobs were available to women in the 1940s. As Liza Mundy explains in her book Code Girls, a single female college graduate could work as a teacher, but she had to quit once she got married, because most schools wouldn't employ married women. They could also be librarians, secretaries, telephone switchboard operators, or “computers"—that is, people who did tedious calculations for astronomers and other scientists. These low-level technical jobs required organization, attention to detail, and a tolerance for painstaking work, qualities that were considered more common in women. Such skills also came in handy for programming early computers.

World War II created new opportunities for women to work. When men left to fight, someone needed to fill their jobs. While millions of women went to work in factories—symbolized by Rosie the Riveter—others got government desk jobs or secret assignments with the military. Hopper ran numbers and calculated rocket trajectories for the Navy, working alongside computer engineers at Harvard. Others were codebreakers: Agnes Meyer Driscoll and Genevieve Grotjan Feinstein helped crack Japanese ciphers, essentially hacking enemy communications. In the United Kingdom, the female cryptanalyst Joan Clarke helped Alan Turing decipher the German Enigma code.

The Women Who Programmed the First Computers

Nearly 200 women worked on the country's first computer, the ENIAC, which was funded by the military and developed to make ballistics computations. Six of them—Kathleen McNulty, Jean Jennings, Betty Snyder, Marlyn Wescoff, Frances Bilas, and Ruth Lichterman—were in charge of programming it. Called “operators," they worked with the cables and switches that told the 30-ton machine what to do. As MIT professor Jennifer S. Light explains in her study of the ENIAC women, programming and computation required training in math, but were considered clerical jobs, or “women's work." Men handled the hardware and women, the software. ENIAC's all-female programming team went unmentioned when it was completed in 1946.

After the war, many government jobs went to men, but women found technology work in the private sector. Hopper was the head programmer at Remington Rand, the company that made the UNIVAC. She developed computer languages that used English words rather than mathematical symbols. Writing in the New York Times Magazine, journalist Clive Thompson explains that coding jobs boomed in the 1950s as businesses used software to process data and payrolls. Since it was a new field, nobody had special training, and any applicant who passed an aptitude test, male or female, could be hired.

In the 1960s, a chronic shortage of computer programmers kept the field open to women. According to Indiana University professor Nathan Ensmenger, women may have accounted for as much as 30% of the country's programmers. Yet as the industry grew, men started taking on the kind of finicky technical jobs that were once the domain of women. Ensmenger found that companies began hiring programmers based on aptitude tests and personality profiles that favored a stereotypical male tech geek. Despite their important role in computing, women started to get shut out of the field.

Rosalind Franklin and the Discovery of DNA

Female "computers" often did tedious calculations for scientists. But the British scientist Rosalind Franklin was one of the few women actually working in a lab—with extraordinary results. During World War II, she studied the chemistry of coal and carbon and made original discoveries that informed the design of gas masks. The research led her to study X-ray crystallography, and she became an expert in the technique.

But it was her work at King's College London that made history when Franklin turned her X-ray skills to the study of DNA. Her detailed X-ray images of DNA showed that its molecule had a helix-shape structure—which paved the way for Francis Crick and James Watson's discovery of the double helix. Franklin died in 1958, four years before her colleagues won the Nobel Prize. Her achievements have led to groundbreaking technology, from AncestryDNA® to the mRNA COVID-19 vaccines.

The Hidden Women Who Helped Launched Us Into Space

Women also found technology jobs at NASA and its predecessor, the National Advisory Committee for Aeronautics (NACA). In 1935, NACA hired five female “human computers" to process flight data. The following decade, it began recruiting African American women for a segregated computer group. Among them were the “Hidden Figures" of Margot Lee Shetterly's bestselling book: Katherine Johnson, Mary Jackson, and Dorothy Vaughan. Johnson calculated trajectories for historic space flights, including Alan Shepherd's Mercury mission in 1961 and John Glenn's orbit around Earth in 1962. (Glenn, who distrusted electronic computers, famously asked Johnson to check the equations by hand before he agreed to fly.)

What the 1950 Census Tells Us About Women Working in Tech

The 1950 Census, which will be released in April 2022, reveals hints of women's roles in the nascent technology industry. The number of women working as office-machine operators more than doubled between 1940 and 1950. In fact, they made up 82% of people in the profession in 1950. These machines would have included early computers like the UNIVAC. Since computer programmers were originally called operators—they moved cables around to tell the machines what to do—some of the female operators in the census would have been what we now call programmers.

Historical records like the 1950 U.S. Census may help you discover the untold stories of women in your family who “rewrote the code” in their own way.