Chaff (countermeasure)

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Modern US Navy RR-144 (top) and RR-129 (bottom) chaff countermeasures and containers. Note how the strips of the RR-129 chaff, bottom, are of different lengths, while those of the RR-144, top, are all the same length. The RR-144 is designed to prevent interference with civil ATC radar systems.




Second World War[edit]




Meanwhile in Germany, similar research had led to the development of Düppel. The German code name was that of the estate on which the first German tests with chaff had been made, circa 1942.[6] Once the idea had been passed to the US, Fred Whipple developed a system (according to Harvard Gazette Archives) for dispensing strips for the USAAF, but it is not known if this was ever used.

A Lancaster dropping chaff (the crescent-shaped white cloud on the left of the picture) over Essen during a thousand-bomber raid

The systems were all essentially identical in concept: small aluminium strips (or wires) cut to one-half of the target radar's wavelength. When hit by the radar, such lengths of metal resonate and re-radiate the signal.[5] Opposing defences would find it almost impossible to distinguish the aircraft from the echoes caused by the chaff. Other radar-confusing techniques included Mandrel,[7] Piperack, and Jostle.




The effect of chaff on the display of a Giant Würzburg radar. The effect of jamming appears in the left "jagged" half of the circular ring, contrasting with the normal "smooth" (unjammed) display on the right half of the circle, with a real target at the 3 o'clock position – on the jammed left side the real target "blip" would have been indistinguishable from the jamming.




Letter from Secretary of the Navy, James Forrestal to Merwyn Bly

Chaff in the United States was co-invented by astronomer Fred Whipple, and Navy engineer Merwyn Bly. Whipple proposed the idea to the Air Force who he was working with at the time.[10] However, initial tests were unsuccessful as the foil strips stuck together and fell as clumps for little or no effect. Bly solved this by designing a cassette such that the strips rubbed against it as they were expelled, gaining an electrostatic charge. Since the strips all had a similar charge they repelled each other, enabling the full countermeasure effect. After the war, Bly received the Navy Distinguished Civilian Service Award for his work.

Falklands War[edit]



See also[edit]


  1. ^ Churchill, Winston Spencer (1951). The Second World War: Closing the Ring. Houghton Mifflin Company, Boston. p. 643. 
  2. ^ Jones. p.39
  3. ^ Jones. p.290
  4. ^ Goebel. section 8.3 The British Begin Countermeasures
  5. ^ a b Jones, p. 291
  6. ^ Jones, p. 299
  7. ^ Mandrel was an airborne jammer targeted at the German Freya radars. Jones. p.295
  8. ^ Jones, pp. 291–299
  9. ^ The Blitz-Then and Now (Volume 3) page 309.
  10. ^ Gewertz, Ken (18 October 2001). "Fred Whipple: Stargazer". Harvard Gazette: The Big Picture. President and Fellows of Harvard College. Retrieved 4 February 2014. 
  11. ^ Sharkey Ward (2000). Sea Harrier Over the Falklands (Cassell Military Paperbacks). Sterling*+ Publishing Company. p. 245. ISBN 0-304-35542-9. 
  12. ^ Morgan, David L. (2006). Hostile Skies: My Falklands Air War. London: Orion Publishing. pp. 59, 73 and photo section. ISBN 0-297-84645-0. 


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