Radar technology gave the Allied forces a decisive edge, but in the early 1940s, magnetrons were notoriously difficult to manufacture. “Spencer was curious about creating a simpler and more efficient way to create magnetrons so they could be mass-produced,” says Rini Paiva, executive vice president of selection and recognition for the National Inventors Hall of Fame. "At the time, only about 20 a day could be manufactured.”
Thanks to Spencer’s work, production soared to 2,600 magnetrons daily, according to Paiva, a breakthrough that helped advance radar capabilities during the war. Spencer’s deep familiarity with radar technology and habit of noticing what others overlooked, led to his most unexpected contribution to history.
The Start of Microwave Cooking
In 1945, Spencer noticed that a candy bar in his pocket had mysteriously melted while testing an active magnetron. Where others might have dismissed the incident as a trivial quirk of the equipment, Spencer saw possibility. His curiosity led him to experiment further, placing popcorn kernels near the magnetron. When they began to pop, his suspicion was confirmed: microwaves could penetrate food and heat it quickly. A follow-up test with an egg resulted in a burst shell and a clear conclusion: Spencer had found a new way to cook.
“Others may have made similar observations before but never capitalized on them while apparently Percy did,” says Joseph A. Schwarcz, director of McGill University’s Office for Science and Society. “As Louis Pasteur said, ‘chance favors the prepared mind.’ I guess Percy's mind was prepared.”
Recognizing the significance of what Spencer uncovered, Raytheon quickly filed a patent for a "microwave cooking process" later that year. But turning a wartime breakthrough into a practical appliance was no small task.