Microwave oven

The microwave oven wasn't invented—it was discovered, accidentally, by an engineer standing too close to hardware built to kill submarines. On a day in 1945 at Raytheon's laboratory in Massachusetts, Percy Spencer noticed the chocolate bar in his pocket had melted while he stood near an active magnetron tube. He wasn't the first to observe this phenomenon, but he was the first to investigate rather than ignore it. Within hours, Spencer was aiming the magnetron at popcorn kernels and watching them explode.

But Spencer's discovery only existed because Britain was losing the Battle of the Atlantic. In September 1939, as German U-boats strangled British shipping lanes, physicists John Randall and Harry Boot at Birmingham University began exploring radical magnetron designs. On February 21, 1940, they tested their first working cavity magnetron: over 400 watts of power at the impossibly short wavelength of 9.8 centimeters. Within months, 25 kilowatts. By 1943, approaching a megawatt.

Britain couldn't mass-produce these devices, so Winston Churchill authorized the Tizard Mission to share the technology with America in September 1940. When Bell Labs tested the British magnetron, they found it produced 10 times the output power at 5 times the frequency of the best American triodes. By war's end, the Allies manufactured magnetrons by the tens of thousands.

This created the adjacent possible for Spencer's 1945 discovery: warehouses full of surplus magnetrons, engineers who understood their physics, and manufacturing infrastructure to produce them at scale. Raytheon filed the first microwave oven patent on October 8, 1945, and built the commercial "Radarange" in 1947. Standing nearly six feet tall, weighing 750 pounds, consuming 3 kilowatts, requiring water cooling, and costing $5,000, it was built like radar equipment because it essentially was radar equipment, repurposed.

For twenty years, the microwave oven remained trapped in this commercial niche. In 1967, Amana introduced the countertop Radarange at $495—small enough for residential kitchens. In 1971, only 1% of U.S. households owned a microwave. By 1975, annual sales hit 1 million units. By 1997, over 90% of households owned one.

The microwave oven demonstrated how war creates the adjacent possible for peace. Without the Battle of the Atlantic, no desperate need for centimetric radar. Without surplus magnetrons, no accidental discovery. Percy Spencer's melted chocolate bar wasn't genius—it was inevitability.