On January 24, 1950, U.S. Patent No. 2,495,429, issued on a Method of Treating Foodstuffs — the microwave oven:

As the story goes, one cay Spencer was standing in front of an active radar set when he noticed that the candy bar in his pocket had melted. Although others had noticed this effect before, Spencer was the first to look into it, eventually creating a microwave oven.

The first microwave ovens that hit the market in 1947 were large commercial oven. It was twenty years before residential versions appeared. The first microwave ovens were marketed by Amana, a division of Spencer’s employer, Raytheon, under the name “Radar Range,” a nod to their radar-based origins.