In the early 1930s the British Air Ministry offered a thousand pounds to anyone who could kill a sheep at 100 yards with a radio death ray. This episode explains how that frantic quest, driven by the belief that the bomber will always get through and by rumours of German engine-stalling weapons in the Black Forest, led the Tizard Committee to Robert Watson-Watt and Arnold Wilkins. Wilkins’s calculation proved the death ray impossible, but his memory of aircraft disturbing Post Office shortwave receivers, and his insight that an 82-foot bomber wingspan matched the half-wavelength of a 50-metre signal, turned detection into a weapon.

From the Daventry experiment in a delivery van in February 1935 to 360-foot steel towers along the coast, we follow the third best rule of engineering, the 1937 exercise where Hugh Dowding watched raw data paralyse his controllers, and the filter rooms and Fruit Machine calculators that turned noise into tracks. The episode then covers the Luftwaffe’s failed bombing of the towers, the jamming duel that produced jitter and yellow-filtered screens, why Germany’s superior Freya radar lost the wizard war for organisational reasons, Operation Big Ben tracking V-2 rockets through interference lobes, and the passive German Klein Heidelberg system that hijacked Chain Home’s own transmissions.

• How the death ray rejection pivoted directly into the question of whether radio could see aircraft
• Why a bomber’s wings resonated as a dipole antenna and broadcast its own position
• The Dowding system, WAAF plotters and the Fruit Machine that solved slant-range trigonometry
• Jitter, phosphor afterglow and the first electronic warfare battle over the Channel
• Chain Home as a network of sensors, cables and filtering hubs that foreshadowed the internet