Chaff (countermeasure)

Chaff, originally called Window by the British, and Düppel by the Second World War era German Luftwaffe (from the Berlin suburb it was first found near), is a radar countermeasure in which aircraft or other targets spread a cloud of small, thin pieces of aluminium, metallized glass fibre or plastic, which either appears as a cluster of secondary targets on radar screens or swamps the screen with multiple returns.

Modern armed forces use chaff (in naval applications, for instance, using short-range SRBOC rockets) to distract radar-guided missiles from their targets. Most military aircraft and warships have chaff dispensing systems for self-defence. An intercontinental ballistic missile may release in its midcourse phase several independent warheads, a large number of decoys, and chaff.

Chaff can also be used to signal distress by an aircraft when communications are not functional. This has the same effect as an SOS, and can be picked up on radar. It is done by dropping chaff every 2 minutes.

Second World War

The idea of using chaff developed independently in the UK and in Germany.

As far back as 1937, R. V. Jones had suggested that a piece of metal foil falling through the air might create radar echoes. In early 1942, a Telecommunications Research Establishment (TRE) researcher named Joan Curran investigated the idea and came up with a scheme for dumping packets of aluminium...
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