Vox Meditantis

When Klára Dán von Neumann described herself as a “mathematical moron,” she could hardly have been more wrong. This brilliant woman, who would become the first person to execute modern-style computer code, consistently underplayed her extraordinary contributions to the birth of computing. Her story exposes a troubling pattern: the systematic erasure of women’s achievements in science, particularly when their work was overshadowed by famous husbands.

From Budapest Ballrooms to Princeton Laboratories

Born into a wealthy Jewish family in Budapest on 18th August 1911, Klára Dán seemed destined for anything but a career in computing. Her childhood was spent in the family’s magnificent villa, where the elite of Hungarian society gathered for elaborate parties that often lasted until dawn. At fourteen, she became Hungary’s national figure skating champion, a remarkable achievement that hinted at the determination that would later define her scientific career.

The Budapest of Klára’s youth was in constant flux. By the time she was ten, she had lived through the Great War and the Hungarian Soviet Republic. Her family fled to Vienna during Béla Kun’s regime, only to return when it collapsed. This early exposure to political upheaval would prove formative for a projects in American history.

Her first three marriages revealed a pattern of restlessness and intelligence seeking its proper outlet. She married Ferenc Engel in 1931, then Andor Rapoch in 1936. Both relationships ended in divorce. It was during her marriage to Engel that she first encountered John von Neumann at a Monte Carlo casino in the 1930s. The meeting was brief but memorable—she instantly recognised the famous mathematician, and he was clearly impressed by her “lively mind”.

The Making of a Programming Pioneer

When John von Neumann’s first marriage ended, he sought out Klára in Budapest. They married in 1938 and immigrated to the United States just as war clouds gathered over Europe. Upon arrival, Klára listed her profession as “housewife”—a designation that would prove laughably inadequate for what she would accomplish.

The attack on Pearl Harbor transformed American society, opening unprecedented opportunities for women in technical fields. Klára seized her chance, securing a position as Head of Statistical Computing Group at Princeton University. This was no clerical role: she was managing complex mathematical computations at one of America’s most prestigious institutions.

When John joined the Manhattan Project at Los Alamos in 1943, Klára remained at Princeton, working in the Office of Population Research until 1946. During this crucial period, she taught herself advanced mathematical techniques that would prove essential to her later programming work. Her natural aptitude for translating abstract mathematical concepts into practical computational methods was becoming apparent, even if she couldn’t see it herself.

Revolutionary Work on the ENIAC

The true measure of Klára’s genius became evident when she joined her husband in Los Alamos after the war. The challenge facing the scientific community was daunting: how to develop more efficient nuclear weapons without wasting precious uranium on actual tests. The answer lay in mathematical simulation, but the available computing technology was primitive and cumbersome.

The ENIAC (Electronic Numerical Integrator and Computer) was a monster of a machine, filling entire rooms with over 17,000 vacuum tubes. Programming it required physically rewiring circuits for each new problem—a laborious process that made the machine more of a glorified calculator than a true computer. John von Neumann recognised that the future lay in stored-program computers, where instructions could be held in memory rather than hardwired into the machine.

This is where Klára’s extraordinary contribution began. Working with Nick Metropolis from Los Alamos, she spent thirty-two days at the Aberdeen Proving Ground in Maryland, working around the clock to transform the ENIAC. They reconfigured the machine to emulate a stored-program computer, using its function tables to store instructions rather than just numerical constants12.

The task required translating John’s complex mathematical flow diagrams into machine language—a process Klára compared to “a very amusing and rather intricate jigsaw puzzle”. Her code would become the first modern-style program ever executed on a computer, running Monte Carlo simulations of nuclear fission processes. These calculations were historically significant not just for their scientific importance, but because they represented the birth of modern computer programming.

Weather Forecasting and Scientific Breakthrough

Klára’s programming expertise soon extended beyond weapons research. In 1950, she played a crucial role in one of computing’s most celebrated achievements: the first computer-generated weather forecast. Working with a team of meteorologists at Aberdeen, she helped create programs that could predict atmospheric conditions—something that had seemed impossible just years earlier.

The project was monumentally challenging. Previous attempts at mathematical weather prediction, notably by Lewis Fry Richardson in the 1920s, had required months of hand calculations to produce forecasts that were already obsolete. Using Klára’s programming and the modified ENIAC, the team produced their first 24-hour weather forecast in approximately 24 hours of computing time—a breakthrough that Richardson himself called an “enormous scientific advance”.

The technical complexity of this achievement cannot be overstated. The team had to develop algorithms that could process data from weather stations across North America, apply complex mathematical models to atmospheric dynamics, and produce meaningful predictions. Klára’s role included not just writing the code, but managing the 100,000 punch cards that served as the system’s memory and ensuring no data was lost during the lengthy calculations.

The Hidden Brilliance Behind the Work

Despite her fundamental contributions, Klára remained painfully self-deprecating about her abilities. Her unpublished memoir, titled “A Grasshopper in Very Tall Grass,” reveals deep insecurities about her mathematical capabilities. She consistently described herself as having “no formal mathematical training,” though this was far from accurate—she had studied calculus at Princeton and possessed an intuitive grasp of complex computational problems that few could match.

This self-doubt reflected the broader context of women’s roles in wartime science. At Los Alamos, wives were often dismissed as “bonus spouses”—women who happened to possess useful skills but were not considered serious scientists in their own right. The culture of secrecy surrounding the Manhattan Project meant that much of women’s work remained invisible to the broader scientific community, making it easier to overlook their contributions in subsequent historical accounts.

Thomas Haigh, the computer historian who has done the most to recover Klára’s story, describes her as a “super-programmer” whose work was fundamental to the development of modern computing. Her papers, buried within her husband’s much larger archive at the Library of Congress and written in Hungarian with difficult handwriting, required extraordinary detective work to decipher. The effort was worthwhile: it revealed a woman whose technical contributions were far more significant than anyone had previously recognised.

Legacy and the Price of Progress

Klára’s later years were marked by both achievement and tragedy. After John’s death from cancer in 1957—likely caused by his work with radioactive materials at Los Alamos—she became the keeper of his scientific legacy. She wrote the foreword to his posthumously published work “The Computer and the Brain” and managed his considerable scientific estate.

In 1958, she married oceanographer Carl Eckart and moved to La Jolla, California. She began writing her memoir, reflecting on a life that had taken her from Hungarian ballrooms to the frontiers of atomic science. But the burden of her experiences, including her work on weapons of mass destruction and the loss of her brilliant husband, may have proved overwhelming.

On 10th November 1963, Klära drove from her La Jolla home to the ocean and walked into the water. She was never seen alive again. The coroner ruled her death a suicide, noting that she had been diagnosed with “anxiety depression with neuroses”. She was just fifty-two years old.

Reclaiming a Hidden History

Klára Dán von Neumann’s story challenges fundamental assumptions about the history of computing. Far from being a field dominated by male “lone geniuses,” early programming relied heavily on women’s contributions—contributions that were systematically minimised or erased from the historical record. Klára’s self-description as a “mathematical moron” reflects not her actual abilities, but the insidious way that brilliant women were conditioned to doubt their own capabilities.

Her technical achievements were extraordinary by any measure. She wrote the first modern computer program, contributed to the development of stored-program computing, and helped create the first computerised weather forecasting system. These accomplishments alone would secure her place in computing history, yet her name remains largely unknown outside specialist circles.

The recovery of Klára’s story is part of a broader effort to correct the historical record and recognise women’s contributions to science and technology. Her papers, painstakingly translated and analysed by dedicated historians, reveal not just technical brilliance but also the human cost of working on humanity’s most destructive weapons. She was, in Thomas Haigh’s words, “there at the creation” of modern computing.

The Continuing Relevance of Her Story

Today, as we confront questions about artificial intelligence, algorithmic decision-making, and the social implications of computing technology, Klára’s story offers important lessons. Her work on Monte Carlo methods now underpins everything from financial modelling to pandemic predictions. Her contributions to weather forecasting helped establish the field of computational meteorology that remains essential to understanding climate change.

Perhaps most importantly, her story reminds us that scientific progress is never the work of isolated individuals but of teams, collaborations, and communities. The “great man” theory of scientific history obscures the contributions of countless women like Klára whose work was essential but whose recognition was delayed or denied entirely.

The mathematical moron who changed the world was never a moron at all. She was a brilliant, complex woman whose contributions to computing were fundamental to the digital age we now inhabit. It is time her story was told in full, not as a footnote to her husband’s achievements, but as the remarkable scientific legacy it truly represents. In recognising Klára Dán von Neumann, we take an essential step towards a more complete and honest understanding of how our modern technological world came to be.

Bob Lynn | © 2025 Vox Meditantis. All rights reserved.