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Fall 2010 | Volume 25 |  Issue 3

In early 1945 Laurence Marshall contemplated the imminent financial ruin of his company. Raytheon had enjoyed a lucrative business supplying the U.S. military with magnetrons, electron tubes that generated microwaves, a key component in the nascent technology of radar and the detection of enemy airplanes. But World War II seemed likely to end soon, and with it Raytheon’s lucrative military contracts. Raytheon needed to come up with something it could sell to civilians. He gathered a half-dozen of his top employees at his house in Cambridge, Massachusetts, and asked, “What shall we do after the war?”

His managers, who had been working 70-hour weeks developing techniques for mass producing magnetrons as well as inventing radar devices for ship and airborne use, were dead tired. But one of them, Percy Spencer, had an idea. What if Raytheon built on its radar expertise and created a microwave oven for consumer use?

Marshall had depended on Spencer since 1925 to turn his abstract ideas into operable devices. Most often this called for a solution in the form of vacuum tubes. Spencer had only a grade-school education, but he had learned the rudiments of vacuum tubes while serving in the Navy during World War I. Inspired by the heroism of the Titanic’s wireless operators, he “got hold of textbooks and taught myself while I was standing watch at night.”

At Raytheon Spencer continued his self-education, assigning one of his engineers to gather all the new vacuum tube patents every week. The engineer then wrote a paragraph-long critique of each patent, focusing on how it might be applied to Raytheon products. Spencer’s careful study of these reports (along with his colleague’s engineering expertise) led to many of Raytheon’s cardinal successes in its first two decades.

During the war it was common in winter for Raytheon engineers walking past banks of magnetrons to warm their hands on the heat they emitted. An oft-told, possibly apocryphal story relates how Spencer walked by a magnetron with a chocolate candy bar in his shirt pocket. The heat melted the candy and gave him the idea that microwaves could be used to heat food. In the early 1940s he and other Raytheon engineers began experimenting with using radar tubes to heat food.

Using radiation to cook food, of course, is nothing new, dating back to meat cooked over glowing coals in prehistoric times. But the visible and infrared radiation that has always been used for cooking cannot penetrate the surface of most foods; the heat only diffuses into the interior. In contrast, microwaves—a type of radio wave—pass through the outer layer of food and heat the interior directly by agitating molecules of water, fats, sugars, and other food components.

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