Chaff (electronic warfare)

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In electronic warfare, which covers the entire electromagnetic spectrum chaff (electronic warfare) is a mass of radar-reflective material that acts as a decoy, reflecting the radar more brightly than the target.

The individual pieces of chaff, which are typically an aluminium film on plastic or glass, need to be cut to dimensions related to the wavelength of the radar considered the greatest threat. There may be different chaff payloads to be used against missiles at different parts of their flight path; one type may be intended to distract midcourse guidance radar while another, final defense form, is intended to seduce the final attack. Chaff may be used in conjunction with other electronic warfare, such as deceptive jammers, and final hard-kill defense systems such as the RIM-116 Rolling Airframe Missile.

Current chaff dispensing usually is in an expendable cartridge that, once leaving the launcher, either bursts into a cloud or spreads as a stream. A shipboard family, for example, includes a Mark 216 RF seduction decoy, Mark 1214 RF distraction decoy, and infrared , an active radar jammer, a Ship-Launched Acoustic Decoy against submarines, and a and dual RF/IR seduction decoy.[1].

Historical forms

Earlier forms might be cut continuously from a roll, or, in the earliest forms, code-named Window by the Royal Air Force in the Second World War, literally thrown out as bundles. The British were hesitant to use it over Germany, concerned that the Germans could copy it and use it on night raids against Britain, but Germany actually had the technology, called Düppel, which they had not used for much the same reason.

Showing that chaff has to be designed for a specific threat, when the Germans changed the frequency of their SN2 airborne intercept radar in 1943, the "Window" then used by the RAF night bombers became useless. [2]

On the night that the invasion fleet moved to the "D-Day" landings of Battle of Normandy, the Royal Air Force ran two deception operations using chaff to simulate false convoys; it is significant that 617 Squadron, usually considered the most accurate bombing squadron in the RAF, was committed to this mission:[3]

  • Operation TAXABLE: 16 Lancasters of 617 Squadron approaching Cap d’Antifer.
  • Operation GLIMMER: 6 Stirlings of 218 Squadron directed at Boulogne

During Operation LINEBACKER II of the Vietnam War, the initial use of chaff, in "corridors" dropped from chaff-laden fighters, did block specific radar beams, but served to mark the flight paths over which the following bombers would approach.[4] One critical tactical change was changing from corridors to clouds.

Launchers

While they can be launched manually, military aircraft usually dispense chaff from magazine-loaded, increasingly intelligent expendable coutermeasures devices such as the AN/ALE-47. Such dispensers usually can release flare (electronic warfare) in a cartridge with the same form factor as the chaff, and even more expendable cartridges, such as radar jammers and intelligence sensors, are in the same package.

Surface vehicles, rather than dropping cartridges, usually shoot small rockets or mortars with warheads packed with chaff. [1] The NATO standard form factors are:

  • 112 mm RBOC (Rapid Bloom Offboard Chaff) launcher
  • 130 mm SRBOC (Super Rapid Bloom Offboard Chaff) launcher

Common launchers are the Mark 36 from United Defense,

References

  1. 1.0 1.1 Sippican, Inc., Off-board countermeasures: anti-ship missile defense system
  2. Murray, Williamson & Allan R. Millett (2001), A War to Be Won: Fighting the Second World War, Harvard University Press, ISBN 0674006801, p. 320
  3. Royal Air Force, D-Day Timeline
  4. Clark, Gregory S. (04 Feb 2002), Linebacker 2: Achieving Strategic Surprise, Naval War College, p. 10