The microwave oven was invented by mistake when an engineer testing a magnetron tube noticed that the radiation from it melted the chocolate bar he had in his pocket.
Fast-forward to 1939 where Spencer, now one of the world?s leading experts in radar tube design, was working at Raytheon as the head of the power tube division. Largely due to his reputation and expertise, Spencer managed to help Raytheon win a government contract to develop and produce combat radar equipment for M.I.T.?s Radiation Laboratory. This was of huge importance to the Allies and became the military?s second highest priority project during WWII, behind the Manhattan Project. It also saw Spencer?s staff rise from 15 employees to 5000 over the course of the next few years.
One day, while Spencer was working on building magnetrons for radar sets, he was standing in front of an active radar set when he noticed the candy bar he had in his pocket melted. Spencer wasn?t the first to notice something like this with radars, but he was the first to investigate it. He and some other colleagues then began trying to heat other food objects to see if a similar heating effect could be observed. The first one they heated intentionally was popcorn kernels, which became the world?s first microwaved popcorn. Spencer then decided to try to heat an egg. He got a kettle and cut a hole in the side, then put the whole egg in the kettle and positioned the magnetron to direct the microwaves into the hole. The result was that the egg exploding in the face of one of his co-workers, who was looking in the kettle as the egg exploded. (source)
If there's one thing I love about history, it's the history of items that were 'accidentally' made. Like, they didn't purposely find a way to heat food, it just kinda happened one day when a chocolate bar melted in the presence of waves. And those facts, for me, are pretty awesome. (That, plus I love science!)