<P> Sir Henry Tizard travelled to the U.S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help (see Tizard Mission). An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, London, was given to the U.S. government in September 1940 . The magnetron was later described by American historian James Phinney Baxter III as "(t) he most valuable cargo ever brought to our shores". Contracts were awarded to Raytheon and other companies for mass production of the magnetron . </P> <P> In 1945, the specific heating effect of a high - power microwave beam was accidentally discovered by Percy Spencer, an American self - taught engineer from Howland, Maine . Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a candy bar he had in his pocket . The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters . To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape . When food was placed in the box with the microwave energy, the temperature of the food rose rapidly . </P> <P> On 8 October 1945, Raytheon filed a United States patent application for Spencer's microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing . </P> <P> In 1947, Raytheon built the "Radarange", the first commercially available microwave oven . It was almost 1.8 metres (5 ft 11 in) tall, weighed 340 kilograms (750 lb) and cost about US $5,000 ($54,000 in 2016 dollars) each . It consumed 3 kilowatts, about three times as much as today's microwave ovens, and was water - cooled . An early Radarange was installed (and remains) in the galley of the nuclear - powered passenger / cargo ship NS Savannah . An early commercial model introduced in 1954 consumed 1.6 kilowatts and sold for US $2,000 to US $3,000 ($18,000 to $27,000 in 2016 dollars). Raytheon licensed its technology to the Tappan Stove company of Mansfield, Ohio in 1952 . They tried to market a large 220 volt wall unit as a home microwave oven in 1955 for a price of US $1,295 ($12,000 in 2016 dollars), but it did not sell well . In 1965, Raytheon acquired Amana . In 1967, they introduced the first popular home model, the countertop Radarange, at a price of US $495 ($4,000 in 2016 dollars). </P>

Where was the first microwave oven placed for testing