At the later age, he discovered that a local paper mill was soon to begin using electricity, a concept little known in his rural home region, and he began learning as much as possible about the phenomenon.
In the Navy he made himself an expert on radio technology: "I just got hold of a lot of textbooks and taught myself while I was standing watch at night."
With his reputation and expertise, Spencer helped Raytheon win a government contract to develop and produce combat radar equipment for M.I.T.’s Radiation Laboratory.
According to legend, one day while building magnetrons, Spencer was standing in front of an active radar set when he noticed the candy bar he had in his pocket melted.
Spencer then created the first true microwave oven by attaching a high-density electromagnetic field generator to an enclosed metal box.
The magnetron emitted microwaves into the metal box blocking any escape and allowing for controlled and safe experimentation.
In 1967 the first more affordable, $495 (equivalent to $4,523 in 2023), and reasonably sized (counter-top) Radarange brand microwave oven was made available for sale, produced by Amana (a division of Raytheon).
He counted Vannevar Bush, Omar Bradley, William Redington Hewlett and David Packard as friends.