Packet of Window radar counter measure foil

Paper and cardboard parcel containing strips of Window radar counter measure foil. To be used in conjunction with Window Launching Machine Mk.1a

Window foil was a radar countermeasure used by the Allied Air Forces during the Second World War. It was designed to jam German radar equipment either by swamping the screens with multiple returns or by appearing as a cluster of secondary targets. The Window was dispensed using the Window Launching Machine Mk.1a (RELAWM35359.001). The machine consisted of an aluminium alloy box, containing three levels of trays for packets of Window. The trays were actuated by a system of chain drives and belts, which fed the individual packets to a chute at the rear of the machine. The chute then dispensed the packets through a hole especially cut in the bomb bay doors of a bomber aircraft. The machine was controlled by the navigator, using a Switch Box fitted with a control switch and indicator light that illuminated as each bundle of Window was released. A formation of aircraft fitted with the machine could release a carefully controlled pattern of Window, efficiently jamming the German radar.