Chaff (radar countermeasure) - AbsoluteAstronomy.com

Chaff, originally called Window by the British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, and Düppel by the Second World War era German

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

Luftwaffe

Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....

(from the Berlin suburb where it was first developed), is a radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

countermeasure

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...

in which aircraft or other targets spread a cloud of small, thin pieces of aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, metallized glass fibre or plastic

Metallised film

Metallised films are polymer films coated with a thin layer of metal, usually aluminium. They offer the glossy metallic appearance of an aluminium foil at a reduced weight and cost...

, which either appears as a cluster of secondary targets on radar

Radar

screens or swamps the screen with multiple returns.

Modern armed forces use chaff (in naval applications, for instance, using short-range SRBOC

Mark 36 SRBOC

The BAE Systems Mark 36 Super Rapid Blooming Offboard Chaff is a short-range mortar that launches chaff or infrared decoys from naval vessels to foil anti-ship missiles...

rockets) to distract radar-guided missile

Missile

Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

s from their targets. Most military aircraft and warships have chaff dispensing systems for self-defence. An intercontinental ballistic missile

Intercontinental ballistic missile

An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...

may release in its midcourse phase several independent warheads, a large number of decoys

Flare (countermeasure)

A flare is an aerial infrared countermeasure to counter an infrared homing surface-to-air missile or air-to-air missile. Flares are commonly composed of a pyrotechnic composition based on magnesium or another hot-burning metal, with burning temperature equal to or hotter than engine exhaust...

, and chaff.

Chaff can also be used to signal distress

Distress signal

A distress signal is an internationally recognized means for obtaining help. Distress signals take the form of or are commonly made by using radio signals, displaying a visually detected item or illumination, or making an audible sound, from a distance....

by an aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

when communication

Communication

Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...

s are not functional. This has the same effect as an SOS

SOS

SOS is the commonly used description for the international Morse code distress signal...

, 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

United Kingdom

and in Germany

Germany

.

As far back as 1937, R. V. Jones

R. v. Jones

R. v. Jones, [1986] 2 S.C.R. 284 is an early leading Supreme Court of Canada decision on the freedom of religion under section 2 of the Canadian Charter of Rights and Freedoms and the right to security of person under section 7.-Background:...

had suggested that a piece of metal foil falling through the air might create radar echoes. In early 1942, a Telecommunications Research Establishment

Telecommunications Research Establishment

The Telecommunications Research Establishment 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 during World War II and the years that followed. The name was...

(TRE) researcher named Joan Curran

Joan Curran

Lady Joan Strothers Curran was a Welsh scientist. She and her husband, Sir Samuel Curran, played important roles in the defense of the allied forces of World War II.-Biography:...

investigated the idea and came up with a scheme for dumping packets of aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

strips from aircraft to generate a cloud of false echoes.
From a practical point of view it was found the most effective version was strips of black paper backed with aluminium foil

Aluminium foil

Aluminium foil is aluminium prepared in thin metal leaves, with a thickness less than , thinner gauges down to are also commonly used. In the USA, foils are commonly gauged in mils. Standard household foil is typically thick and heavy duty household foil is typically .The foil is pliable, and...

cut to strips exactly 27 centimetres by 2 centimetres and packed into bundles each weighing one pound .

The Head of the TRE

Telecommunications Research Establishment

, A. P. Rowe

Albert Percival Rowe

Albert Percival Rowe was a British physicist and senior research administrator who had a major role in the development of Radar before and during World War II....

, code-named the device as "Window".

Meanwhile in Germany, similar research had led to the development of Düppel. 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

United States Army Air Forces

The United States Army Air Forces was the military aviation arm of the United States of America during and immediately after World War II, and the direct predecessor of the United States Air Force....

, but it is not known if this was ever used.

The systems were all essentially identical in concept: small aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

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. Opposing defences would find it almost impossible to pick out the "real" aircraft from the echoes from the chaff. Other radar-confusing techniques included Mandrel, Piperack, and Jostle.

However, unaware of the opposing air force's knowledge of the chaff concept, planners felt that using it was even more dangerous than not, since, as soon as it was used, the enemy could easily duplicate it and use it against them. In particular, the British government's leading scientific adviser, Professor Lindemann

Frederick Lindemann, 1st Viscount Cherwell

Frederick Alexander Lindemann, 1st Viscount Cherwell FRS PC CH was an English physicist who was an influential scientific adviser to the British government, particularly Winston Churchill...

, balefully pointed out that if the RAF

Royal Air Force

The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

used it against the Germans, the Luftwaffe

Luftwaffe

would quickly copy it and could launch a new Blitz

The Blitz

The Blitz was the sustained strategic bombing of Britain by Nazi Germany between 7 September 1940 and 10 May 1941, during the Second World War. The city of London was bombed by the Luftwaffe for 76 consecutive nights and many towns and cities across the country followed...

. This caused concern in RAF Fighter Command

RAF Fighter Command

RAF Fighter Command was one of three functional 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, gaining recognition in the Battle of Britain. The Command continued until 17 November 1943, when...

and Anti-Aircraft Command

Anti-Aircraft Command

Anti-Aircraft Command was a British Army command of the Second World War that controlled the anti-aircraft artillery units of the British Isles.-History:...

, who managed to suppress the use of Window until July 1943. At this time, it was felt the new generation of centimetric radars available to Fighter Command would deal with any Luftwaffe response to RAF Bomber Command use.

Examination of the Würzburg radar

Würzburg radar

The Würzburg radar was the primary ground-based gun laying radar for both the Luftwaffe and the German Army during World War II. Initial development took place before the war, entering service in 1940. Eventually over 4,000 Würzburgs of various models were produced...

equipment brought back to the UK during Operation Biting

Operation Biting

Operation Biting, also known as the Bruneval Raid, was the codename given to a British Combined Operations raid on a German radar installation in Bruneval, France that occurred between 27–28 February 1942 during World War II...

and subsequent reconnaissance revealed to the British that all German radars were operating in no more than three major frequency ranges, and thus were prone to jamming

Radio jamming

Radio jamming is the transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without first checking whether it is in use, or without being able to hear stations using the frequency...

. "Bomber" Harris, Commander-in-Chief (C-in-C) of RAF Bomber Command

RAF Bomber Command

RAF Bomber Command controlled the RAF's bomber forces from 1936 to 1968. During World War II the command destroyed a significant proportion of Nazi Germany's industries and many German cities, and in the 1960s stood at the peak of its postwar military power with the V bombers and a supplemental...

, finally got approval to use Window as part of Operation Gomorrah, the fire raids against Hamburg

Hamburg

-History:The first historic name for the city was, according to Claudius Ptolemy's reports, Treva.But the city takes its modern name, Hamburg, from the first permanent building on the site, a castle whose construction was ordered by the Emperor Charlemagne in AD 808...

.

The first aircrew trained to use Window were 76 squadron

No. 76 Squadron RAF

No. 76 Squadron is a squadron of the Royal Air Force. It was formed during World War I as a home defence fighter squadron and in its second incarnation during World War II flew as a bomber squadron, first as an operational training unit and later as an active bomber squadron...

. Twenty-four crews were briefed on how to drop the bundles of aluminised

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

-paper strips (treated-paper was used to minimise the weight and 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 were spectacular. The radar guided master searchlights wandered aimlessly across the sky. The AA 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. A vast area of Hamburg was devastated with the loss of only 12 bombers. Squadrons quickly had special chutes fitted to their bombers to make the deployment even easier. Seeing this as a development that made it safer to go on ops, many crews got in as many trips as they could before the Germans found a countermeasure.

Although the metal strips puzzled the German civilians at first, the German scientists knew exactly what they were because they had developed Düppel themselves and refrained from using it for exactly the same reasons as Lindemann had pointed out to the British. Thus 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 refrained from doing so fearing that if they did so the other side would 'learn the trick' and use it against themselves.

The use of Window rendered the ground-controlled 'Himmelbett' (German for "canopy bed") fighters of the Kammhuber Line

Kammhuber Line

The Kammhuber Line was the name given to the German night air defense system established in July 1940 by Colonel Josef Kammhuber.- Description :...

unable to track their targets in the night sky and left radar-guided guns and spotlights

Searchlight

A searchlight is an apparatus that combines a bright light source with some form of curved reflector or other optics to project a powerful beam of light of approximately parallel rays in a particular direction, usually constructed so that it can be swiveled about.-Military use:The Royal Navy used...

useless. In response to this, a new tactic, called Wilde Sau

Wilde Sau

Wilde Sau was the term given by the Luftwaffe, during World War II, to the technique by which British night bombers were mainly engaged by single-seat fighter planes.- Origins :...

, or 'Wild Sow', was developed by Oberst Hajo Herrmann

Hajo Herrmann

Hans-Joachim 'Hajo' Herrmann was a Luftwaffe bomber pilot and later after the end of World War II, focusing his activities as a lawyer on civil and criminal law. In World War II, he was a high ranking and influential member of the Luftwaffe. He was also a recipient of the Knight's Cross of the...

to cope with the lack of accurate ground guidance, and led to the creation of three new fighter wings dedicated to these tactics, numbered JG 300

Jagdgeschwader 300

Jagdgeschwader 300 was a Luftwaffe fighter-wing of World War II. JG 300 was formed on June 26, 1943 in Deelen as Stab/Versuchskommando Herrmann, from July 18, 1943 as Stab/JG Herrmann, and then finally redesignated on August 20, 1943 to Stab/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), and allow the fighters to visually acquire their targets, often against the fires and searchlights below. A few of the single seat fighters used by these new wings had special installations of the FuG 350 Naxos

Naxos radar detector

The FuG 350 Naxos radar warning receiver was a World War II German countermeasure to SHF band centimetric wavelength radar produced by a cavity magnetron...

radar detection gear to spot British bombers at night.

A lesser known fact is that the Luftwaffe used this technology just six weeks after the above-mentioned Hamburg raid. The German strips were cut into 80 centimetre by 1.9 centimetre lengths and first dropped during a raid on 7-8 October 1943. In a series of raids in 1943, and the 'mini-blitz' of Operation Steinbock

Operation Steinbock

Operation Steinbock was the nocturnal Second World War Luftwaffe offensive operation to destroy British military and civilian targets in southern England, between January and May 1944. The attacks were mainly in and around the Greater London area...

between February and May 1944, Düppel allowed German bombers to once again attempt to operate over London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

. Although theoretically effective, the small number of bombers, notably in relation to the RAF's now-large night fighter

Night fighter

A night fighter is a fighter aircraft adapted for use at night or in other times of bad visibility...

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 their Düppel.

Falklands War

Chaff was heavily used by British warships in the Falklands War

Falklands War

The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...

.

During the war, British Sea Harrier aircraft lacked their conventional chaff-dispensing mechanism. Therefore Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

engineers designed an impromptu delivery system of welding rods, split pins and string, which allowed six packets of chaff to be stored in the airbrake

Air brake (aircraft)

In aeronautics, air brakes or speedbrakes are a type of flight control surface used on an aircraft to increase drag or increase the angle of approach during landing....

well and be deployed in flight. It was often referred to as the "Heath Robinson chaff modification", due to its complexity.

External links

BBC: The History of Radar
Obituary of Joan Curran
Joan Curran
Lady Joan Strothers Curran was a Welsh scientist. She and her husband, Sir Samuel Curran, played important roles in the defense of the allied forces of World War II.-Biography:...

in The Independent, Feb 19, 1999 by Tam Dalyell

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Second World War

Falklands War

See also

External links