Bundle of Window

Window was the codename for strips of aluminium foil, now more commonly referred to as Chaff, which produced a deceptive echo, similar to that of an aircraft, on enemy radar screens.

The RAF first used Window during the Hamburg bombing raid in July 1943. It was not used earlier because of fears that the Luftwaffe would replicate it for use against the British radar systems during their own bombing raids. The concept had, however, already been considered in Germany but was not pursued because of similar fears – that its use would provide the RAF with an effective tool to counter German radar.