# The Melted Chocolate Bar That Invented the Microwave Oven > In 1945, American engineer Percy Spencer was working for the company Raytheon on military equipment using magnetrons, the tubes that generate microwaves - Author: Maxime Marquette - Publisher: MadMax (https://mad-max.co) - Section: Reportage - Published: 2026-07-07 - Canonical URL: https://mad-max.co/en/article/la-barre-de-chocolat-fondue-qui-a-invente-le-four-a-micro-ondes ## Key takeaways - Spencer noticed a chocolate bar in his trouser pocket had melted while he worked near an active magnetron. - He tested the effect with popcorn kernels, then with an egg in a pierced kettle that exploded. - He quickly filed a patent describing a microwave cooking process; the article notes he eventually held more than 150 patents. - The first commercial model, the Radarange, launched by Raytheon in 1947, weighed over 300 kilograms and cost about 5,000 dollars, so it was limited to restaurants, cafeterias and ships. - Compact, affordable models appeared in the early 1960s, but the microwave only took hold in American households in the 1970s. ## Introduction: a discovery born from a pocket accident ### A radar engineer in the wrong place, at the right time In **1945**, American engineer **Percy Spencer** was working for the company **Raytheon** on **military equipment** using **magnetrons**, the tubes that generate **microwaves** used notably in the **radar systems** developed during the **Second World War**. Spencer, a self-taught engineer recognized for his **exceptional technical expertise** despite formal schooling that ended very early, spent long hours testing these devices in the lab. According to accounts documented by the **Library of Congress** in its files on everyday technological mysteries, Spencer one day noticed, while working near an **active magnetron**, a **strange sensation** in his trouser pocket. That is the precise moment when one of the most famous accidental invention stories of the twentieth century begins. ### A melted chocolate bar that changes everything Checking his pocket, Spencer discovered with astonishment that a **chocolate bar** he had slipped in earlier that day had literally **melted**, with no **visible heat source** that could have caused it directly. Intrigued by this unexpected phenomenon, he quickly understood that the **electromagnetic waves** emitted by the magnetron could be responsible for this **unexplained melting**. *There is something delightful in the idea that a major technological discovery of the twentieth century owes its origin to a candy bar forgotten in a pocket, rather than to a scientific hypothesis carefully planned in advance.* ## Improvised experiments that confirm the hunch ### The popcorn test Far from settling for this **chance observation**, Percy Spencer decided to push his hunch further by placing **corn kernels** near the magnetron to see what would happen. According to accounts reported by the **National Inventors Hall of Fame**, the kernels quickly turned into **popcorn** before his eyes, spectacularly confirming that **microwaves** could indeed cook certain foods from a distance, without direct contact with a flame or a heating element. Emboldened by this striking confirmation, Spencer continued his tests with other foods, including an **egg** placed in a pierced kettle, which literally exploded under the **internal pressure** generated by the rapid microwave cooking, splattering debris on the face of a colleague present during this improvised but now historic experiment. ### From curiosity to a patented invention Convinced of the potential of this discovery, Percy Spencer quickly filed a **patent** describing a **cooking process** using **microwaves**, laying the theoretical and technical groundwork for what would become, a few years later, the commercial microwave oven. This **speed of reaction**, remarkable for the time, reflects a **sharp sense of technical opportunity** in this largely self-taught engineer. Records kept by the **Smithsonian Institution** note that Spencer would go on to obtain more than **150 patents** over the course of his **career**, an impressive figure that places this discovery of **culinary microwaves** among the most famous, but far from the only significant technical contribution from this prolific inventor. ## The Radarange, a metal monster reserved for industry ### A machine as heavy as a refrigerator The first commercial microwave oven, named the **Radarange** and launched by Raytheon in **1947**, had very little in common with the compact appliances found in home kitchens today. Weighing more than **300 kilograms** and standing nearly six feet tall, this first model looked more like an **industrial cabinet** than a simple **household appliance**. According to information gathered by **Business Insider** in its files on the history of landmark technological inventions, this imposing size was due to the need to **effectively cool the magnetron** as well as the **miniaturization limits** typical of this pioneering era of industrial electronics. ### A price tag reserved for restaurants and ships The cost of this first **Radarange** came to about **5,000 dollars** at the time, a sum equivalent to several tens of thousands of dollars today once adjusted for **inflation**, making the appliance completely **out of reach for the general public**. Only certain **restaurants**, industrial cafeterias, and merchant marine ships could afford to invest in this **revolutionary but extremely costly cooking technology**. This initial exclusivity, documented by several historical analyses of the appliance sector, considerably delayed the mass-market adoption of a technology that, despite its promise, would remain confined to professional use for nearly two decades after its initial invention. ## The slow democratization of a cooking technology ### Decades before entering households It would take until the early **1960s** to see progressively more **compact** and more **affordable** versions of the microwave oven appear, as technological advances made it possible to reduce both the size of the magnetron and the manufacturing costs tied to this still relatively young technology. According to documents gathered by **Smithsonian Magazine** in its files on the history of domestic innovation, it was really only during the **1970s** that the microwave oven began to take hold massively in **American households**, before gradually winning over the rest of the Western world in the decades that followed. ### A quiet revolution in kitchens worldwide Today, the microwave oven has become a **nearly universal household appliance**, present in the vast majority of **Western homes** and in a growing number of kitchens around the world, illustrating a remarkable trajectory of technological democratization from its strictly industrial and military origins. This present-day ubiquity contrasts sharply with the appliance's initial exclusivity, a reminder that many technologies now considered perfectly ordinary often had commercial beginnings reserved for an industrial or institutional elite before their mass adoption by the general public. ### A discovery that theory alone would never have allowed The story of the microwave oven illustrates with rare clarity how some of the most enduring inventions in modern technological history arise not from a carefully formulated theoretical hypothesis, but from a chance empirical observation, immediately followed by rigorous scientific curiosity to understand the underlying mechanisms. Historians of science regularly point out that this type of **accidental discovery**, also called serendipity, has played a disproportionate role in the history of major technological innovations, from penicillin to X-rays, all the way to this microwave oven born from a simple candy bar forgotten in a trouser pocket. ### The importance of attentive observation in everyday life What truly sets Percy Spencer apart from many other engineers who probably observed similar phenomena without paying them any attention is his ability to turn a trivial sensation into a legitimate scientific question, then into a systematic, methodically documented experiment. *This story constantly reminds me that most great discoveries do not arise in the solemn silence of a theoretical laboratory, but in the very real mess of everyday life, where a trouser pocket can sometimes prove more instructive than hours of learned calculations.* ## Percy Spencer's lasting legacy in our kitchens ### An inventor unknown to the general public Despite the **current ubiquity** of the microwave oven in households around the world, the name **Percy Spencer** remains largely unknown to the general public, unlike other, more famous inventors whose names are directly tied to their respective technological creations. This relative anonymity contrasts with the institutional recognition Spencer nonetheless receives within the scientific and technical community, notably through his **induction** into the **National Inventors Hall of Fame**, which officially celebrates his **decisive contribution** to a technology that has become indispensable. *I always find it strange how easily we remember the name of a famous inventor for some minor gadget, while almost completely forgetting the name of the man whose chance discovery transformed the way billions of people prepare their meals every single day.* ### A technology still constantly evolving Since the first massive industrial models of the 1940s, microwave oven technology has continued to evolve, gaining compactness, energy efficiency, and features, all while retaining the same fundamental physical principle discovered almost by chance by Percy Spencer in the aftermath of the Second World War. **Contemporary manufacturers** continue to innovate around this now decades-old technology, integrating **combined cooking** functions, **digital connectivity**, and greater energy efficiency, proof that even an invention this old can keep reinventing itself over the following decades. ## What Raytheon's patents reveal about this pioneering era ### A technological race fueled by war The context of the **Second World War** played a decisive role in the accelerated development of radar and microwave technologies, as Allied governments invested massively in military research to improve aerial and naval detection. This technological race, documented by several American institutional archives, indirectly created the ideal conditions for Percy Spencer's chance discovery, who would probably never have had access to such a powerful magnetron in peacetime. **Raytheon's laboratories**, mobilized almost entirely for the war effort during this period, had a unique technical environment, conducive to experiments that few other civilian companies could have carried out at the same time, for lack of equivalent equipment. ### From military technology to civilian use The transition from a technology initially designed for strictly military purposes to a civilian application as mundane as cooking food illustrates a frequent phenomenon in the history of **wartime technologies**, many applications of which are later repurposed for peaceful, domestic uses once the conflict ends. *There is something almost ironic about a technology designed to spot enemy aircraft ending up warming our everyday meals, as if industrial history sometimes enjoys these unexpected twists that turn a weapon of war into a familiar household object.* ## Conclusion: an invention born of chance, now indispensable ### A lesson in scientific humility The story of the microwave oven is a powerful reminder that **technological innovation** does not always follow the straight path we sometimes imagine, but often proceeds through unexpected detours, where the chance observation of an ordinary phenomenon can open the way to a lasting technical revolution, profoundly transforming the daily habits of billions of people around the world. This **trajectory**, from the melted chocolate bar to the universally common microwave oven, continues to be told in countless books devoted to the **history of science** and technology, since it so clearly illustrates the sometimes unpredictable mechanisms by which some of the most enduring inventions come into being. ### An ordinary object carrying an extraordinary story Today, when millions of people mindlessly reheat their meals in just a few minutes, very few think about the **self-taught engineer** whose curiosity over a melted candy bar allowed, entirely by chance, the emergence of a technology that has become absolutely **central to contemporary kitchens** around the world. This historical anecdote, however surprising, is ultimately a reminder that the most ordinary objects in our daily lives often carry remarkably improbable invention stories, ones that deserve to be rediscovered and told to the people who use them every day without giving them a second thought. It is worth remembering, too, that Spencer never set out to reinvent how the world cooks dinner. He was simply paying attention, and that quiet habit of noticing the small, unexplained details of an ordinary afternoon turned out to be worth far more than any grand theoretical ambition. **By Maxime Marquette, columnist** ## Columnist's transparency note ### Editorial stance I am not a journalist but a **columnist and analyst**. My expertise lies in observing and analysing the geopolitical, economic and strategic dynamics that shape our world. My work is to take political strategies apart, to understand global economic movements, to put the decisions of international actors in context and to offer analytical perspectives on the changes that are redefining our societies. I do not claim the cold objectivity of traditional journalism, which stops at reporting facts. **I claim analytical clarity**, rigorous interpretation and a deep understanding of the complex issues that concern us all. My role is to give meaning to the facts, to place them in their historical and strategic context, and to offer a critical reading of events. ### Method and sources This text keeps the basic distinction between **verified facts and interpretive analysis**. The rule never changes: a factual claim is published only when a verifiable source supports it, and the sources this article actually used are listed under **Sources**, never here. **Primary source families** used by the publication, when the story has them: official statements from governments and international institutions, public statements by political leaders, reports from intergovernmental organisations, dispatches from recognised international news agencies. **Secondary source families**: specialised publications, internationally recognised news media, analyses from established research institutions, reports from industry organisations. When an article cites statistical, economic or geopolitical data, it comes from the institutions that produce it (intergovernmental organisations, central banks, national statistics offices), and the exact institution is named under **Sources**. ### Nature of the analysis The analyses, interpretations and perspectives in the analytical sections of this article are a **critical, contextual synthesis** based on the information available, the trends observed and the expert comments cited in the sources consulted. My role is to interpret these facts, to set them in the context of today's geopolitical and economic dynamics, and to give them a coherent meaning within the larger story of the changes shaping our time. These analyses reflect expertise built through continuous observation of international affairs and an understanding of the strategic mechanisms that drive global actors. This article describes a documented state of affairs on its publication date, not a prediction: later developments may shift its outlook. No update is promised in advance; when an article is corrected or completed, the change is dated in the text. ## Sources ### Primary sources - Library of Congress — file on the invention of the microwave oven — accessed 2026 - National Inventors Hall of Fame — profile of Percy Spencer — accessed 2026 - Smithsonian Institution — file on landmark technological inventions — accessed 2026 ### Secondary sources - Business Insider — account of the history of the Radarange — 2026 - Smithsonian Magazine Innovation — file on the democratization of the microwave — 2026 - History.com — history of the accidental invention of the microwave — 2026 --- Source: Maxime Marquette, MadMax. When citing, name the author and link https://mad-max.co/en/article/la-barre-de-chocolat-fondue-qui-a-invente-le-four-a-micro-ondes