Percy Spencer’s discovery that microwave energy could heat food led Raytheon to seek a patent for technology that would eventually transform kitchens around the world.
THE UNIVERSAL RECORD
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Brad Socha | October 8, 2026 | 5:29 AM EST
On October 8, 1945, engineer Percy L. Spencer filed a U.S. patent application describing a practical method for cooking food with microwave energy. Developed through his work at Raytheon, the idea took technology closely associated with wartime radar and pointed it toward an entirely different destination: the kitchen.
The microwave oven did not immediately become the compact appliance familiar today. Early machines were enormous, expensive and intended mainly for commercial kitchens. But Spencer’s 1945 patent application established an important technical foundation for an appliance that would eventually change how millions of people cooked, reheated and designed food.
Its origins were closely tied to one of the defining technologies of the Second World War.
From Radar to the Microwave
At the centre of the story was the magnetron, a vacuum tube capable of producing high-frequency electromagnetic waves.
During the Second World War, cavity magnetrons became crucial components of radar systems. Raytheon was heavily involved in producing magnetrons for the Allied war effort, and Spencer had become an important figure in improving their manufacture. His work helped Raytheon dramatically increase magnetron production.
Spencer was largely self-educated. Born in Maine in 1894, he left school young and later joined the U.S. Navy, where he developed an interest in radio technology. He eventually joined the company that became Raytheon and built a career around radio, vacuum tubes and radar.
Then came the observation that would become part of technological folklore.
While working around a magnetron in 1945, Spencer reportedly discovered that a candy bar in his pocket had begun to melt. Smithsonian research recounts that he subsequently experimented with popcorn, which popped when exposed to microwave energy.
The famous story contains an important qualification. Later accounts from people involved in Raytheon’s microwave research described the discovery less as a single dramatic moment and more as a progression of chance observations followed by deliberate experimentation. Researchers had noticed heating effects around microwave equipment before.
Spencer’s contribution was recognizing that the phenomenon could be developed into a useful method of cooking.
Experiments with food followed, and Raytheon began working toward a controlled cooking system.
On October 8, 1945, Spencer filed U.S. patent application Serial No. 620,919, assigned to Raytheon Manufacturing Company. The document was titled “Method of Treating Foodstuffs.”
Rather than claiming that electromagnetic energy itself had never been used to heat food, Spencer’s application acknowledged earlier work at lower frequencies. His advance was the practical use of wavelengths in the microwave region.
The patent described generating microwave energy, concentrating it within a restricted space and exposing food to that energy long enough to cook it.
The application eventually became U.S. Patent 2,495,429, granted on January 24, 1950.
A Kitchen Revolution That Took Decades
The concept worked, but turning it into a household appliance was another matter.
Raytheon’s first commercial microwave oven, known as the Radarange, appeared in 1947. Smithsonian records describe the first unit purchased by a Cleveland restaurant as costing about $3,000.
Early machines bore little resemblance to today’s countertop ovens. They stood roughly six feet tall and weighed more than 750 pounds. Their size, cost and technical requirements meant microwave cooking initially belonged primarily in restaurants and other commercial settings rather than ordinary homes.
Engineers gradually made the technology smaller and more practical.
Raytheon licensed microwave technology to the Tappan Stove Company, which developed an oven for domestic use during the 1950s. The Tappan RL-1 was still far from a mass-market appliance. Early versions were expensive and built into kitchens rather than being the inexpensive countertop machines that later became commonplace.
A major transition came after Raytheon acquired Amana Refrigeration in 1965.
In 1967, Amana introduced a more practical countertop Radarange priced at $495. Although still expensive for many households, the machine represented an important step toward making microwave cooking a consumer technology.
As manufacturing improved and prices declined, adoption accelerated. The microwave also influenced the food industry. Frozen meals, snacks and other products increasingly could be designed around rapid reheating, while kitchens gained an appliance capable of performing some tasks in minutes rather than requiring a conventional oven or stovetop.
The deeper significance of October 8, 1945, therefore lies beyond a single patent filing.
The microwave oven is an example of technology moving unexpectedly from military research into civilian life. Radar development had demanded powerful, reliable sources of microwave energy. Spencer and his colleagues recognized that the same energy could solve an entirely different problem.
What began with magnetrons built for wartime radar eventually became an appliance used to warm coffee, defrost dinner and pop popcorn.
The transition was neither instantaneous nor the work of one accidental discovery alone. It required wartime advances in electronics, Spencer’s experimentation, Raytheon’s engineering and decades of further development.
But the patent application filed on October 8, 1945, captured the essential idea: microwave energy could be deliberately concentrated and controlled to cook food.
A technology created to help detect distant aircraft and ships was beginning its journey toward one of the most familiar places imaginable, the kitchen.
Sources:
Google Patents — Percy L. Spencer, Method of Treating Foodstuffs, U.S. Patent 2,495,429
https://patents.google.com/patent/US2495429A/en
Smithsonian Institution, National Museum of American History — Tappan Model RL-1 Microwave Oven
https://www.si.edu/object/tappan-model-rl-1-microwave-oven%3Anmah_1088040
Smithsonian Institution, Lemelson Center for the Study of Invention and Innovation — The Devil Is in the Details: Researching an Inventor’s Biography
https://invention.si.edu/invention-stories/devil-details-researching-inventors-biography
MIT Lemelson — Percy Spencer
https://lemelson.mit.edu/resources/percy-spencer
National Inventors Hall of Fame — Percy L. Spencer
https://www.invent.org/inductees/percy-l-spencer
IEEE Spectrum — A Brief History of the Microwave Oven
https://spectrum.ieee.org/a-brief-history-of-the-microwave-oven
About the Author
Brad Socha is the founder of The Universal Record, focused on sourced, factual global reporting. Coverage includes international news, geopolitics, technology, and major developments.