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 Wild Boar tactics, the American electrostatic cartridge, Japan’s deceiving paper, Doppler filtering, notching, jammer-plus-chaff techniques, the improvised Harrier modification of the Falklands War, and the aluminum-coated glass fibers used by modern fighters.

• The tuning-fork physics of why half-wavelength strips overwhelm radar receivers
• How Operation Biting’s raid on a Wurzburg radar gave Britain the confidence to finally use Window
• Why only 12 of 791 bombers were lost on the first Hamburg raid
• Merwin Bly’s static-electricity solution to chaff clumping in the slipstream
• How Doppler radar, notching, and illuminated chaff turned a paper trick into an electronic arms race