The world entered the computer age right here in Philadelphia. It is fairly well known that the modern computer’s birthplace was in 1946 at the Moore School of Electrical Engineering at the University of Pennsylvania, with ENIAC, the Electronic Numerical Integrator And Computer. What is less well known is that its first programmers were a team of six women, four of whom were native Philadelphians.

At that time, the Moore School was male-only, a stipulation of the 1923 endowment from Alfred Fitler Moore, whose family business produced wire for use in telegraphs, telephones, and electricity. In the 1940s, the term “computer” meant a person who solved mathematical equations by hand. The United States Army was a major employer of computers, for calculating thousands of ballistics trajectories, which varied with the type of gun used, and even the climate in which it would be fired. A human computer would take about 30 hours to calculate a trajectory using differential calculus equations. The ENIAC’s mechanical precursor, the Differential Analyzer, could do the same work in about 15 minutes, but required cross-checking for accuracy by a human computer.

Although women were often employed as computers in some fields, this military work required not only skills in using a desktop calculator, but also a knowledge of higher math and physics. As the United States entered World War II, men educated in those typically male dominated fields were in short supply, so opportunities for women opened up.

Philadelphia was chosen as a site for the Army’s Ballistic Research Labs (BRL) as it was not too far from the Aberdeen Proving Ground (APG) in Maryland where the weapons were tested, and it was a major city with several large universities, plus several women’s colleges.

After employing dozens of women calculators, six were ultimately chosen to move on to the ENIAC project. Kay McNulty [later Antonelli] grew up in Chestnut Hill, graduated from John Hallahan Catholic Girls’ High School at 311 N. 19th Street, and earned a degree in mathematics from Chestnut Hill College. Fran Bilas [later Spence] grew up in South Philadelphia, graduated from South Philadelphia High School for Girls, and also earned a degree in mathematics from Chestnut Hill College, where she met and became friends with McNulty. Marlyn Wescoff [later Metzler] grew up in West Philadelphia, graduated from West Philadelphia High School, and earned a degree in mathematics from Temple University. Betty Snyder [later Holberton] was born in Philadelphia and raised in Narberth. As the daughter and granddaughter of astronomers, she was encouraged to pursue her ability in mathematics, but was discouraged at the University of Pennsylvania by a professor who felt women shouldn’t be in the field, and so she studied English and journalism instead.

Two other mathematicians moved to Philadelphia to join the project: Ruth Lichterman [later Teitelbaum], with a degree from Hunter College in New York City and Jean Jennings [later Bartik], a graduate of Northwest Missouri State Teachers’ College.

ENIAC’s home was in the basement of the Howard E. Pepper Building at 200 S. 33rd Street, now called the Moore School Building. Originally designed by the architects Morris & Erskine for the Pepper musical instrument company, in 1926, Alfred Bendiner, an architect employed by the firm of Paul Phillipe Cret, provided alterations and the building was officially occupied by The Moore School.

ENIAC was a modular computer employing 18,000 vacuum tubes and with individual parts performing different functions via inputs and outputs of IBM punch card technology. It occupied a 50 by 30-foot area of the building, with 40 computing panels arranged in a U-shape along three walls. It weighed 30 tons and used 150 kilowatts of power to operate. ENIAC used a base 10 system. Its designers, J. Presper Eckert and John Mauchly, initially thought about using base 2, like today’s computers, but decided it would be too difficult and time consuming to convert. Base 10 is the major reason why ENIAC needed so many vacuum tubes in its circuitry.

The ENIAC programmers’ job was far more laborious than that of today’s computer programmers. With no programming language or operating system, they had to figure out how to interface with it and then hand-wire the computer with cables and switches to create numerous very small steps that ENIAC could perform, to ultimately calculate a complicated mathematical problem. Now, instead of 30 hours to complete by hand, a ballistic calculation could be done by ENIAC in a few seconds.

ENIAC was introduced to the public on Valentine’s Day, 1946. On its front page the next day, The New York Times described “an amazing machine,” calling it “the new electronic speed marvel.” It went on to report about the ceremonies and dinner to be given to “a group of Government and scientific men” following a demonstration of the machine. Although the demonstration was given by Marlyn Wescoff and Ruth Lichterman, none of the six programmers were invited to the other events.

Wartime ballistics trajectories were the impetus for creating ENIAC, but supply chain delays caused it to be completed after the end of the war. However, the contract between the Army Ballistic Research Labs and the Moore School “called for ENIAC to be delivered with a working ballistics trajectory program,” according to the Times article. ENIAC was moved to Aberdeen, Maryland in 1949 and was in use until October 1955.

After World War II, women were encouraged to leave their wartime jobs in factories and on farms to free up employment for returning soldiers. Yet, in the case of ENIAC, there was no one else who knew how to program it, so the six were encouraged to stay on.

Later, Eckert and Mauchly left the Moore School to start their own company, were joined by Holberton and Jennings, and together developed UNIVAC, one of the first commercial computers. Holberton is credited with creating the first software that allowed a computer to be operated by keyboard commands instead of switches.

Eckert and Mauchly are firmly ensconced in the standard narrative of the history of computers, but, until recently, the programmers were hardly mentioned or omitted altogether, as in the 2013 book The Smithsonian’s History of America in 101 Objects. The chapter on ENIAC describes the costs, dates, and numbers of components, but the only names included are those of Eckert and Mauchly. In his history comic book series from the 1990s, Pennsylvania Profiles, author and illustrator Patrick Reynolds includes a chapter on ENIAC and again mentions the two men, but not the programmers, even though his illustration portrays two women operating the computer.

More recently, other outlets have taken steps to correct the omission, such as University of Pennsylvania’s Engineering School, the IT History Society, Wikipedia, a few authors and documentary filmmakers, and the organization Workforce Innovation, Trust, and Influence, which sponsors the Women in Technology Hall of Fame, where the “ENIAC 6” are inductees.

In October 2023, the Army Research Laboratory Supercomputing Resource Center had a public dedication of new supercomputing systems. According to an Army press release, “The five new supercomputers, with a sixth one coming online next year, are named after the original six programmers of the world’s first general purpose scientific computer, the ENIAC, which stands for Electronic Numerical Integrator and Computer. It began operation on Aberdeen Proving Ground in 1947. The original six programmers were: Jean Jennings, Marlyn Wescoff, Ruth Lichterman, Betty Snyder, Frances Bilas and Kay McNulty.”

Parts of ENIAC are ensconced in various museum collections around the country. The University of Pennsylvania has on display four of the original 40 panels of the ENIAC on the ground floor of the Moore School Building. Other repositories include the Smithsonian’s National Museum of American History, the University of Michigan in Ann Arbor, the Computer History Museum in Mountain View, California, and the U.S. Army Ordnance Museum in Aberdeen.

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