This page is a compact dated outline. Longer stories, such as the magnetron’s origins or the safety debates, are covered elsewhere on the site, so each entry here is short. Dates marked “about” or “around” are approximate in the sources.
Timeline
1940. At the University of Birmingham in Britain, John Randall and Harry Boot build a working cavity magnetron, a powerful source of short radio waves for radar. It is one of the key wartime technologies in the development of radar detection.
1940 to 1945. The magnetron design is shared with American laboratories and manufacturers. Several companies produce it in quantity, including Raytheon.
Around 1945. Percy Spencer, an engineer at Raytheon, notices that microwaves from a magnetron heat food. The best-known retelling involves a candy bar that melted in his pocket. This detail is anecdotal, and accounts differ on the food involved.
October 1945. Raytheon files a patent application covering the use of microwaves for treating food. The patent itself was granted several years later, in 1950.
About 1947. Raytheon introduces the first commercial microwave oven, the Radarange. It is large, water-cooled and costly, aimed at restaurants, railways and ships.
Late 1940s to 1950s. A small number of commercial units are installed. Companies and researchers explore other uses of microwave heating, including industrial drying and reheating prepared meals.
About 1955. A range manufacturer launches the first oven marketed for homes. It is built-in and priced at well over a thousand dollars. Sales are low.
1965. Raytheon acquires Amana, a maker of home appliances, giving it a route to the consumer market.
1967. Amana introduces a countertop Radarange that runs from a normal outlet and sells for under $500. Many sources treat this as the start of the mass market.
1968. The United States passes the Radiation Control for Health and Safety Act, which allows federal standards for products that emit radiation.
Early 1970s. A federal performance standard for microwave ovens takes effect, with limits on leakage and requirements for door interlocks. Public worries about safety are a visible issue at this time.
1970s. Electronic controls built with integrated circuits appear, and turntables become common. More manufacturers, including firms in Japan, expand production, and prices fall.
1980s. Microwave ovens become common in homes. Packaged foods designed for microwave heating, such as bagged popcorn, spread through grocery stores. Many households also buy their first microwave during this decade, often using it alongside household refrigerators with freezer compartments.
1990s. A large majority of households in the United States and several other wealthy countries own a microwave oven. Over-the-range models and combined microwave and convection ovens are widely sold.
2000s onward. The appliance is a standard fixture, with features such as sensors and inverter power supplies. Smaller improvements continue, but the basic design remains recognizable from the 1960s.
Reading the timeline
Several parts of the timeline are firmly documented: the Birmingham magnetron in 1940, Raytheon’s patent filing, the Radarange name and the existence of the 1967 countertop model. Others are looser. The year of Spencer’s discovery is usually given as 1945, but descriptions of the event vary. Prices and sales figures in this period are given in round numbers in most sources, and the exact figures differ between accounts.
Who gets the credit
Credit for the microwave oven is shared in several ways.
- Randall and Boot for the magnetron that made high-power microwaves practical.
- Percy Spencer and his colleagues at Raytheon for recognizing the heating effect and developing it into a product.
- The engineers at Amana and other firms for reducing size and cost.
- The wartime research networks that spread radar technology between countries.
Earlier work on heating with high-frequency radio energy also existed. Physicians and engineers had studied warming of tissue by radio-frequency fields in the 1920s and 1930s, a field known as diathermy, so Spencer’s observation did not come from nowhere. Saying that one person invented the microwave oven is therefore a simplification, even though Spencer’s name is the one most often attached to the story.
A note on milestones
Some summaries claim that the microwave oven was invented to replace the stove or that its discovery was entirely accidental. Both statements are oversimplified. The appliance did not replace the stove, and the discovery came from a laboratory with equipment designed for radar, where somebody was well placed to notice an unexpected effect and follow it up. What turned that observation into a product took two decades and a series of smaller engineering steps.