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Chaff, originally called Window by the British and ''Düppel'' by the
Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...
era
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German '' Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the '' Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabt ...
(from the Berlin suburb where it was first developed), is a
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
countermeasure A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...
in which aircraft or other targets spread a cloud of small, thin pieces of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
, metallized glass fibre or
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
, which either appears as a cluster of primary targets on
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
screens or swamps the screen with multiple returns, in order to confuse and distract. Modern armed forces use chaff (in naval applications, for instance, using short-range
SRBOC The BAE Systems Mark 36 Super Rapid Bloom Offboard Countermeasures Chaff and Decoy Launching System (abbreviated as SRBOC or "Super-arboc") is an American short-range decoy launching system (DLS) that launches radar or infrared decoys from naval ...
rockets) to distract radar-guided
missile In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket ...
s from their targets. Most military aircraft and warships have chaff dispensing systems for self-defense. An
intercontinental ballistic missile An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than , primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads). Conventional, chemical, and biological weapo ...
may release in its midcourse phase several independent warheads as well as
penetration aid A penetration aid (or "penaid") is a device or tactic used to increase an intercontinental ballistic missile (ICBM) warhead's chances of penetrating a target's defenses. These can consist of both ''physical devices'' carried within the ICBM (as p ...
s such as decoy balloons and chaff. Modern radar systems can distinguish chaff from target objects by measuring the
Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...
; chaff quickly loses speed compared to an aircraft and thus shows a characteristic change in frequency that allows it to be filtered out. This has led to new techniques where the chaff is further illuminated by an additional signal from the target vehicle with the proper Doppler frequency. This is known as JAFF (jammer plus chaff) or CHILL (chaff-illuminated).


Second World War

The idea of using chaff developed independently in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
, the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
and
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
. In 1937, British researcher Gerald Touch, while working with
Robert Watson-Watt Sir Robert Alexander Watson Watt (13 April 1892 – 5 December 1973) was a Scottish pioneer of radio direction finding and radar technology. Watt began his career in radio physics with a job at the Met Office, where he began looking for accura ...
on radar, suggested that lengths of wire suspended from balloons or parachutes might overwhelm a radar system with false echoes and
R. V. Jones Reginald Victor Jones , FRSE, LLD (29 September 1911 – 17 December 1997) was a British physicist and scientific military intelligence expert who played an important role in the defence of Britain in by solving scientific and technical pr ...
had suggested that pieces of metal foil falling through the air might do the same. In early 1942,
Telecommunications Research Establishment The Telecommunications Research Establishment (TRE) was the main United Kingdom research and development organization for radio navigation, radar, infra-red detection for heat seeking missiles, and related work for the Royal Air Force (RAF) ...
(TRE) researcher
Joan Curran Joan, Lady Curran (26 February 1916 – 10 February 1999), born Joan Elizabeth Strothers, was a Welsh physicist who played important roles in the development of radar and the atomic bomb during the Second World War. She invented chaff, a ra ...
investigated the idea and came up with a scheme for dumping packets of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
strips from aircraft to generate a cloud of false echoes. An early idea was to use sheets the size of a notebook page; these would be printed so they would also serve as propaganda leaflets. It was found that the most effective version was strips of black paper backed with
aluminium foil Aluminium foil (or aluminum foil in North American English; often informally called tin foil) is aluminium prepared in thin metal leaves with a thickness less than ; thinner gauges down to are also commonly used. Standard household foil is typ ...
, exactly and packed into bundles each weighing . The head of the TRE,
A. P. Rowe Albert Percival Rowe, Order of the British Empire, CBE (23 March 1898 – 25 May 1976), often known as Jimmy Rowe or A. P. Rowe, was a radar pioneer and university vice-chancellor. A British physicist and senior research administrator, he played ...
, code-named the device "Window". In Germany, similar research had led to the development of ''Düppel''. The German code name came from the estate where the first German tests with chaff took place, circa 1942. Once the British had passed the idea to the US via the
Tizard Mission The Tizard Mission, officially the British Technical and Scientific Mission, was a British delegation that visited the United States during WWII to obtain the industrial resources to exploit the military potential of the research and development ( ...
, Fred Whipple developed a system for dispensing strips for the
USAAF The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...
, but it is not known if this was ever used. The systems used the same concept of small
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
strips (or wires) cut to a half of the target radar's wavelength. When hit by the radar, such lengths of metal resonate and re-radiate the signal. Opposing defences would find it almost impossible to distinguish the aircraft from the echoes caused by the chaff. Other radar-confusing techniques included airborne jamming devices codenamed Mandrel, Piperack and Jostle. Mandrel was an airborne jammer targeted at the German Freya radars. Ignorance about the extent of knowledge of the principle in the opposing air force led planners to judge that it was too dangerous to use, since the opponent could duplicate it. The British government's leading scientific adviser,
Professor Lindemann Frederick Alexander Lindemann, 1st Viscount Cherwell, ( ; 5 April 18863 July 1957) was a British physicist who was prime scientific adviser to Winston Churchill in World War II. Lindemann was a brilliant intellectual, who cut through bureau ...
, pointed out that if the
Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) an ...
(RAF) used it against the Germans, the ''
Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German '' Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the '' Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabt ...
'' would quickly copy it and could launch a new Blitz. This caused concern in
RAF Fighter Command RAF Fighter Command was one of the commands of the Royal Air Force. It was formed in 1936 to allow more specialised control of fighter aircraft. It served throughout the Second World War. It earned near-immortal fame during the Battle of Brita ...
and
Anti-Aircraft Command Anti-Aircraft Command (AA Command, or "Ack-Ack Command") was a British Army command of the Second World War that controlled the Territorial Army anti-aircraft artillery and searchlight formations and units defending the United Kingdom. Origin ...
, who managed to suppress the use of Window until July 1943. It was felt that the new generation of centimetric radars available to Fighter Command would cope with ''Luftwaffe'' retaliation. Examination of the Würzburg radar equipment brought back to the UK during Operation Biting (February 1942) and subsequent reconnaissance revealed to the British that all German radars were operating in no more than three frequency ranges, making them prone to jamming. Arthur Travers "Bomber" Harris, Commander-in-Chief (C-in-C) of
RAF Bomber Command RAF Bomber Command controlled the Royal Air Force's bomber forces from 1936 to 1968. Along with the United States Army Air Forces, it played the central role in the strategic bombing of Germany in World War II. From 1942 onward, the British bo ...
, finally got approval to use Window as part of Operation Gomorrah, the week long bombing campaign against
Hamburg Hamburg (, ; nds, label=Hamburg German, Low Saxon, Hamborg ), officially the Free and Hanseatic City of Hamburg (german: Freie und Hansestadt Hamburg; nds, label=Low Saxon, Friee un Hansestadt Hamborg),. is the List of cities in Germany by popul ...
. The first aircrew trained to use Window were in 76 Squadron. Twenty-four crews were briefed on how to drop the bundles of aluminised-paper strips (treated-paper was used to minimise the weight and to maximise the time that the strips would remain in the air, prolonging the effect), one every minute through the flare chute, using a stopwatch to time them. The results proved spectacular. The radar-guided master searchlights wandered aimlessly across the sky. The
anti-aircraft Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based ...
guns fired randomly or not at all and the night fighters, their radar displays swamped with false echoes, utterly failed to find the bomber stream. For over a week, Allied attacks devastated a vast area of Hamburg, resulting in more than 40,000 civilian deaths, with the loss of only 12 out of the 791 bombers on the first night. Squadrons quickly had special chutes fitted to their bombers to make chaff deployment even easier. Seeing this as a development that made it safer to go on operations, many crews got in as many trips as they could before the Germans found a counter-countermeasure. Although the metal strips puzzled the German civilians at first, German scientists knew exactly what they were – ''Düppel'' – but had refrained from using it for the same reasons as Lindemann had pointed out to the British. For over a year the curious situation arose where both sides of the conflict knew how to use chaff to jam the other side's radar but had refrained from doing so for fear of their opponent replying in kind. Window rendered the ground-controlled ''Himmelbett'' (canopy bed) fighters of the Kammhuber Line unable to track their targets in the night sky and rendered the early UHF-band ''B/C'' and ''C-1'' versions of the airborne intercept Lichtenstein radar (following the capture of a Junkers Ju 88R-1 night fighter by the British in May 1943 equipped with it) useless, blinding radar-guided
guns A gun is a ranged weapon designed to use a shooting tube (gun barrel) to launch projectiles. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, ...
and spotlights dependent on the ground-based radar. ''Oberst'' Hajo Herrmann developed ''
Wilde Sau ''Wilde Sau'' ( Lit. wild sow; generally known in English as "Wild Boar") was the term given by the ''Luftwaffe'' to the tactic used from 1943 to 1944 during World War II by which British night bombers were engaged by single-seat day-fighter air ...
'' (Wild Boar) to cope with the lack of accurate ground guidance and led to the formation of three new fighter wings to use the tactic, numbered JG 300, JG 301 and JG 302. Ground operators would radio-direct single-seat fighters and night fighters to areas where the concentrations of chaff were greatest (which would indicate the source of the chaff) for the fighter pilots to see targets, often against the illumination from fires and searchlights below. A few of the single-seat fighters had the FuG 350 ''Naxos'' device to detect H2S radar (the first airborne, ground scanning radar system) emissions from the bombers. Six weeks after the Hamburg raid, the ''Luftwaffe'' used ''Düppel'' in lengths during a raid on the night of 7/8 October 1943. In raids in 1943 and the "mini-blitz" of
Operation Steinbock Operation Steinbock (german: Unternehmen Steinbock), sometimes called the Baby Blitz, was a strategic bombing campaign by the German Air Force (the Luftwaffe) during the Second World War. It targeted southern England and lasted from January to M ...
between February and May 1944, ''Düppel'' allowed German bombers again to attempt operations over
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
. Although theoretically effective, the small number of bombers, notably in relation to the large RAF
night-fighter A night fighter (also known as all-weather fighter or all-weather interceptor for a period of time after the Second World War) is a fighter aircraft adapted for use at night or in other times of bad visibility. Night fighters began to be used ...
force, doomed the effort from the start. The British fighters were able to go aloft in large numbers and often found the German bombers in spite of ''Düppel''. The Germans obtained better results during the
air raid on Bari The air raid on Bari (german: Luftangriff auf den Hafen von Bari, it, Bombardamento di Bari) was an air attack by German bombers on Allied forces and shipping in Bari, Italy, on 2 December 1943, during World War II. 105 German Junkers Ju 88 b ...
in Italy, on 2 December 1943, when Allied radars were deceived by the use of ''Düppel''. Following the British discovery of it in 1942 by Joan Curran, 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 he was working with at the time. Early tests failed as the foil strips stuck together and fell as clumps to little or no effect. Bly solved this by designing a cartridge that forced the strips to rub 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 {{infobox military award , name = , image = DON Distinguished Civilian Service.png , image_size = 100px , caption = Department of the Navy Distinguished Civilian Service Medal , presenter = Depart ...
for his work. In the Pacific Theatre, Navy Lieutenant Commander Sudo Hajime invented a Japanese version called , or "deceiving paper". It was first used with some success in mid 1943, during night battles over the
Solomon Islands Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capit ...
. Competing demands for the scarce aluminum necessary for its manufacture limited its use. On February 21, 1945, during the
Battle of Iwo Jima The Battle of Iwo Jima (19 February – 26 March 1945) was a major battle in which the United States Marine Corps (USMC) and United States Navy (USN) landed on and eventually captured the island of Iwo Jima from the Imperial Japanese Army (IJA ...
, was successfully used prior to a
Kamikaze , officially , were a part of the Japanese Special Attack Units of military aviators who flew suicide attacks for the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, intending ...
attack on the .


Falklands War

British warships in the
Falklands War The Falklands War ( es, link=no, Guerra de las Malvinas) was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British dependent territories in the South Atlantic: the Falkland Islands and its territorial ...
(1982) made heavy use of chaff. During this war, British Sea Harrier aircraft lacked their conventional chaff-dispensing mechanism. Therefore,
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against Fr ...
engineers designed an improvised delivery system of
welding rod Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
s,
split pin A split pin, also known in the United States of America as a cotter pin or cotter key, is a metal fastener with two tines that are bent during installation, similar to a staple or rivet. Typically made of thick wire with a half-circular cross ...
s and string, which allowed six packets of chaff to be stored in the airbrake well and be deployed in flight. It was often referred to as the "
Heath Robinson William Heath Robinson (31 May 1872 – 13 September 1944) was an English cartoonist, illustrator and artist, best known for drawings of whimsically elaborate machines to achieve simple objectives. In the UK, the term "Heath Robinson contr ...
chaff modification", due to its complexity.


JAFF and CHILL

One of the important qualities of chaff is that it is lightweight, allowing large amounts to be carried. As a result, after release it quickly loses any forward speed it had from the aircraft or rocket launcher, and then begins to fall slowly to the ground. From the viewpoint of an enemy radar, the chaff quickly decays to zero relative velocity. Modern radars use the
Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...
to measure the line-of-sight velocity of objects, and can thus distinguish chaff from an aircraft, which continues to move at high speed. This allows the radar to filter out the chaff from its display. To counteract this filtering, the JAFF or CHILL technique has been developed. This uses an additional jammer broadcaster on the aircraft to reflect a signal off the chaff cloud that has the proper frequency to match that of the aircraft. This makes it impossible to use Doppler shift alone to filter out the chaff signal. In practice, the signal is deliberately noisy in order to present multiple false targets. In essence, the JAFF technique is a low-cost offboard decoy, moving the jammers from the launcher platform to the decoy, and using the chaff as a reflector to provide angular separation.


Modern chaff

While foil chaff is still used by certain aircraft, such as the
Boeing B-52 Stratofortress The Boeing B-52 Stratofortress is an American long-range, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air ...
bomber, this type is no longer manufactured. The chaff used by aircraft such as the
Fairchild-Republic A-10 Thunderbolt II The Fairchild Republic A-10 Thunderbolt II is a single-seat, twin- turbofan, straight-wing, subsonic attack aircraft developed by Fairchild Republic for the United States Air Force (USAF). In service since 1976, it is named for the Repub ...
,
McDonnell Douglas F-15 Eagle The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather tactical fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force selected McDonnell Douglas's ...
,
General Dynamics F-16 Fighting Falcon The General Dynamics F-16 Fighting Falcon is a single-engine multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it evolved into a success ...
, and
McDonnell Douglas F/A-18 Hornet The McDonnell Douglas F/A-18 Hornet is an all-weather, twinjet, twin-engine, supersonic aircraft, supersonic, carrier-based aircraft, carrier-capable, Multirole combat aircraft, multirole combat aircraft, designed as both a Fighter aircraft, ...
consists of aluminium-coated glass fibres. These fibre "
dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system ...
s" are designed to remain airborne for as long as possible, having a typical diameter of 1 mil, or 0.025 mm, and a typical length of to over . Newer "superfine" chaff has a typical diameter of . The chaff is carried in tubular cartridges, which remain attached to the aircraft, each typically containing around 3 to 5 million chaff fibres. The chaff is ejected from the cartridge by a plastic piston driven by a small pyrotechnic charge. Chaff - Radar Countermeasures
at GlobalSecurity.org (website), Alexandria, Vermont. Retrieved 5 November 2020.


See also

*
Anti-ballistic missile An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles (missile defense). Ballistic missiles are used to deliver nuclear, chemical, biological, or conventional warheads in a ballistic flight trajec ...
*
Countermeasure A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...
*
Infrared countermeasure An infrared countermeasure (IRCM) is a device designed to protect aircraft from infrared homing ("heat seeking") missiles by confusing the missiles' infrared guidance system so that they miss their target (electronic countermeasure). Heat-see ...
*
Electronic countermeasure An electronic countermeasure (ECM) is an electrical or electronic device designed to trick or deceive radar, sonar, or other detection systems, like infrared (IR) or lasers. It may be used both offensively and defensively to deny targeting info ...
* Flare (countermeasure) *
SRBOC The BAE Systems Mark 36 Super Rapid Bloom Offboard Countermeasures Chaff and Decoy Launching System (abbreviated as SRBOC or "Super-arboc") is an American short-range decoy launching system (DLS) that launches radar or infrared decoys from naval ...
(Super Rapid-Blooming Offboard Chaff), a shipboard chaff system


References


Sources

*Goebel, Greg
''The Wizard War: WW2 & The Origins Of Radar''
v.2.0.2, retrieved 2021-05-26 * *


External links


BBC: The History of Radar
* Obituary of
Joan Curran Joan, Lady Curran (26 February 1916 – 10 February 1999), born Joan Elizabeth Strothers, was a Welsh physicist who played important roles in the development of radar and the atomic bomb during the Second World War. She invented chaff, a ra ...
i
The Independent, Feb 19, 1999 by Tam Dalyell





RAF Window
at the International Bomber Command Centre Digital Archive. {{RAF WWII Strategic Bombing British inventions Military equipment introduced from 1940 to 1944 Military technology Penetration aids Weapons countermeasures World War II Allied electronics World War II British electronics