Manhattan Project Women ‘Calculators’ Paved Way For Modern Computers

The wives of scientists, members of the Women’s Army Corps, and local civilians were recruited to perform these calculations on the mechanical calculators during the Manhattan Project. Courtesy/AHF

According to one Manhattan Project calculator, ‘the machines were big, clumsy, slow, and always breaking down’. Courtesy/Atomic Heritage Foundation

By Heather McClenahan
Los Alamos Historical Society

Science and technology experts tell us that the smart phones we hold in our hands have more computing power than the computers that sent astronauts and the Saturn V rockets to the moon. Imagine, then, attempting to calculate the world’s most complex mathematical problems involving blast waves, differential equations, interactions of atomic nuclei, and other numerical simulations—often on the timescale of billionths of a second—with slide rules and mechanical calculators.

That’s what happened during the Manhattan Project. Physicists and other scientists on the project needed long, often tedious mathematical calculations done quickly. They relied on a group of women, who were called “calculators” and “computers,” and who often had little or no training in math. These women sat for long hours, hand writing numbers or punching them in on limited and imperfect mechanical desk calculators.

One Los Alamos department head is rumored to have said, “We hire girls because they work better, and they’re cheaper.” Additionally, almost all of the supervisors and managers were men. Still, many women appreciated the opportunity to work in a technical field when most working women were supposed to be teachers or nurses.

In the landmark book, Their Day in the Sun: Women of the Manhattan Project, authors Ruth Howes and Caroline Herzenberg devoted a chapter to explaining how the calculators and computers worked, who they were, the tools they used, and how their efforts led to the development of what would be the world’s first electronic computers.

The author’s wrote, “Computers had not yet been invented. Electric punched-card machines were available for certain calculations, but most problems were solved on heavy, old-fashioned desk-top calculators…The operators of the machines would take the equations and punch the numbers into their calculators over and over, performing a single operation or a set of operations on a long series of numbers in a human analog to today’s parallel processors.”

Marchant, Frieden, or Monroe desk calculators (you can see a Marchant calculator on display in the Los Alamos History Museum) gave way to IBM punch card machines as the project progressed. The new machines performed at about the same speed as the group of women, but they did not get tired and make mistakes at the end of a shift as the humans did.

Bernice Brode served as a computer and devoted a chapter of her book, Tales of Los Alamos: Life on the Mesa 1943-1945, to her work in the technical area of the laboratory. “Our immediate supervisor was Mary Frankel, who set up the problems for us to run through the machines. The resulting figures were taken to the graph room, in the charge of Bob Davis, and were put on his graphs. The idea was to make curves, and all the scientists took the greatest interest in the progress of the curves. If our figures put a jog in one of these curves, the figures were wrong—not vice versa.”

In spite of the tedious work, the group maintained a sense of humor. Brode mentioned that while she took her job seriously, Frankel had a Ph.D. in mathematics but would put the math problem sheets for the computers in a basket labeled “Free—Take One.”

Brode also joked that the most serious business, community gossip, was conducted along with the calculations when the “computers” desks were gathered to face one another.

In the end, though, their work made a contribution toward those smart phones we have today.

As Howes and Herzenberg summed it up: “Female mathematicians and calculators played a major part in organizing and carrying out this massive effort. In the process, several of them gained experience that led them to prominent roles in the rapid development of computers after the war.”

The authors posit, in fact, that the “vast number of calculations needed for the creation of the atomic bomb also helped trigger the development of the first electronic computers.”

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