How a Raytheon Scientist Accidentally Invented the Microwave Oven

If you’ve ever nuked a Hot Pocket or used your microwave to warm up some leftovers, you have a comedy of errors to thank for the convenience. The invention of the all-too-common microwave came down to an accident involving a Raytheon engineer, an experiment with some radar equipment, and a chocolaty peanut candy bar.

In 1945, World War I Navy veteran Percy Spencer was working at the American Appliance Company in Cambridge, Massachusetts, which would later become Raytheon. Though he dropped out of school at age 12, Spencer had an affinity for electrical systems and continued to expand his knowledge of them when he joined the Navy. He also explored chemistry, calculus, and radio systems on his own, according to the Atomic Heritage Foundation.

“I just got hold of a lot of textbooks and taught myself while I was standing watch at night,” Spencer recalled.

The hard work paid off when he left the military and began working as a defense contractor at Raytheon. 

During World War II, Raytheon invested heavily in radar tools with the rise of submarine and aircraft warfare. Spencer was an integral member of a team tasked with building out the technology. “During World War II, he and his co-workers produced large amounts of radar equipment,” MIT records indicated. “One such piece of equipment was the compact cavity magnetron, a high-powered vacuum tube that generates microwaves.”

His work on the magnetron, which vastly improved radar technology, garnered him a Distinguished Public Service Award from the U.S. Navy. But that’s not the work on which he’d hang his hat. Rather, Spencer would gain fame for a mistake that led to the mass proliferation of the microwave oven.

A pocketed candy bar was exposed to the microwaves the magnetron gave off when Spencer stood a little too close to it. And while the average technician might have simply been disappointed to realize their midafternoon snack melted, Spencer saw a spark of innovation, realizing the gooey goodie had major implications for the future of food.

“Intrigued, he sent out for unpopped popcorn,” writes the New England Historical Society. “When it popped in front of the magnetron, he realized that microwaves could cook food.”

On October 8, 1945, Spencer and the team filed for a patent on the technology. It was approved in January 1950, and Raytheon began manufacturing the commercial microwave oven, called “Radarange.” According to the University of Maine, the invention is listed as Patent #2,495,429 Method of Treating Foodstuffs. 

In the filing, Spencer called it “one of the objects of my present invention to provide an efficient method of employing electromagnetic energy for the cooking of foodstuffs.”

Spencer might have been jazzed about his accidental creation, but the microwave didn’t really gain the kind of widespread popularity it enjoys today for another two decades. 

There were a few reasons for that. The early versions of the Radarange were six-feet tall and weighed 750 pounds. Those early iterations were seen as industrial—more for restaurant use. To scale down to household size, Raytheon bought an appliance company called Amana Refrigeration in 1965, which allowed it to create and release the first countertop microwave oven for around $500 in 1967.

Another hurdle to consumer adoption? Fear of radiation. 

Sales didn’t really take off until the 1970s, after the Bureau of Radiological Health, part of the FDA, began a thorough testing process to ensure microwaves didn’t emit dangerous levels of radiation, and set standards for microwave ovens that took effect in 1971. The New York Times notes: All units produced since that year were “safe, the bureau maintains, when used according to the manufacturer’s directions.”

George Foerstner, the original founder of Amana, who stayed on at the company when he sold it to Raytheon, was also helpful in both the development and marketing of the household microwave. According to the Times, when the Radarange came under attack over safety fears, Foerstner mounted “a fervent defense that included bringing in a scientist from the National Aeronautics and Space Administration who said he would be willing to sit on a Radarange for a year.”

By 1974, the FDA estimated, about half a million household microwaves were in use across America. Over the 75 years since its inception, 1.7 billion microwave ovens have been sold. Now, you can find a small one for as low as $35, if your home isn’t already equipped with one permanently. Typically, they come in two forms: over range and countertop. Top brands include Panasonic, General Electric, and Toshiba.

It’s hard to imagine life without this kitchen staple, but we just as easily might never have seen the happy accidental microwave had Spencer instead shoved an apple in his pocket on that fateful day.