That ordinary box in the kitchen actually came out of World War II's radar laboratories. And at the start of the story is a candy bar melting in an engineer's pocket. In the video we said "chocolate", because that's mostly how the story is told; but most sources just say "candy bar". Its exact type isn't known.
A radar master who never finished school
Percy Spencer was born in Maine in 1894. According to Wikipedia he didn't even finish grammar school and had no electrical engineering education; he taught himself mathematics, physics and chemistry largely on his own. At 18 he joined the US Navy.
In 1939 he took charge of the power tube division of Raytheon. He found a more efficient way to make magnetron tubes, the heart of radars, and raised production from 100 to 2,600 a day. According to Wikipedia, he also had a hand in Raytheon winning the contract to produce wartime radar equipment for MIT's Radiation Laboratory. So when the bar in his pocket melted, there were very few people in the world who knew the magnetron better than he did.
1945: the bar that melted in a pocket
According to APS News, Spencer noticed that the candy in his pocket had melted while he was standing next to a working radar set. Many people might have brushed it off as a glitch or a coincidence; Spencer was curious.
The first food he deliberately "cooked" was popcorn: he put corn kernels next to the magnetron and the kernels began to pop. The second try didn't go as well. He put an egg in a kettle; the egg exploded and, according to APS, splattered a skeptical colleague.
Raytheon filed its US patent application for the microwave cooking method on October 8, 1945.
Radarange: an oven as tall as a refrigerator
The first commercial microwave oven came to market under the name "Radarange". Here sources differ slightly: APS News says 1946, Wikipedia says 1947. The measurements are far too large to compare with today's:
- About 1.8 meters tall,
- 340 kilograms in weight,
- 3 kilowatts of power consumption (about three times today's ovens, according to Wikipedia),
- A water-cooled structure.
These ovens were not for homes but for hotels, restaurants and ships. According to Wikipedia, early models were rented for $5 a day ($150 a month). APS gives the price as $5,000 for the time and calculates that in today's money this exceeds $50,000. According to APS, one of the first Radarange units, weighing over 300 kilos, was installed on a ship called the Savannah. So the first microwaved meals were heated not in a kitchen but in the middle of the sea.
| Then | Now |
|---|---|
| About 1.8 m tall | A box that fits on a kitchen counter |
| 340 kg | A box one person can carry |
| Water-cooled | Fan-cooled |
| For rent to hotels and restaurants | In nearly every home |
The microwave comes down to the countertop
It took more than twenty years for the microwave to enter homes. Raytheon bought the Amana company in 1965 and put the first countertop Radarange on sale in 1967 for $495. Wikipedia calculates that this price is equivalent to about $5,000 in 2025 dollars. So it was still a luxury appliance, but it now fit in a kitchen.
A small note in passing: in the story we keep saying "microwave," but the name of Raytheon's first commercial product also clearly shows the radar origins of the business. "Radarange" reads like a combination of the words radar and range (cooker).
The real lesson of Spencer's story may be this: other engineers had stood next to the same radar set too. The difference was that he saw the melted bar in his pocket not as a "problem" but as a "question".
The legacy of the inventor who never finished school
Spencer died on September 8, 1970 in Newton, Massachusetts, at the age of 76. He never had a formal engineering degree, but according to Wikipedia he received the US Navy's Distinguished Public Service Award, was elected to the American Academy of Arts and Sciences, received an honorary doctorate from the University of Massachusetts and was inducted into the Hall of Fame of inventors.
The technology we use today to heat something in thirty seconds in the kitchen is actually a by-product of a tube developed for wartime radars. And the person who noticed it was a self-taught master.
Which small coincidence that we walk past unaware today, do you think, could turn into an ordinary household appliance of the future?