In the middle of World War II, the most advanced radar networks on the planet could be disabled by strips of shiny paper tossed from an airplane. This episode explores the history and physics of chaff, first known by the British code name Window, and how four separate powers, the UK, Germany, the United States, and Japan, independently invented the same countermeasure. We break down why metal strips cut to half a radar's wavelength act like tiny dipole antennas, swamping screens with false echoes.

From Joan Curran's trial-and-error design of black paper backed with aluminum foil to the year-long standoff in which neither Britain nor Germany dared use the weapon first, we follow chaff to its debut over Hamburg in July 1943, when a crewman with a stopwatch pushed one bundle down the flare chute every minute. The story continues through German ...