The device heating leftovers in your kitchen contains the same technology that arguably won World War II for the Allies. This episode traces the cavity magnetron, a copper block with holes drilled into it, from its origins as a corporate patent workaround at General Electric in 1921 to its role as a top-secret submarine-hunting radar component and finally to the more than one billion units now sitting in microwave ovens around the world.

We explain how a magnetic field bends electrons into a spiraling cloud that makes the copper cavities resonate like air blown across a bottle, why 1920s versions melted their own cathodes, and why the German military rejected Hans Hollmann's 1935 design over frequency drift. Then we follow John Randall and Harry Boot's 1940 breakthrough at Birmingham, the Tizard Mission that carried a prototype to America i ...