My Science School

On New Year’s Eve, 1986, one of the most disastrous fires since the Second World War killed 97 people in a hotel in Puerto Rico. Workers at the hotel, the Dupont Plaza in San Juan, had become angry over the lack of a pay settlement, and two of them used methylated spirit to set fire to cardboard boxes and other rubbish in an empty ballroom.

Within 15 minutes the flames had engulfed the entire ground floor and trapped hotel guests on the top floor of the 21-storey building. Many of the 1400 occupants had to be rescued by helicopter. As well as the 97 dead, there were 140 people injured.

Investigators from the US Bureau of Alcohol, Tobacco and Firearms were on the scene while the fire was still raging. When they examined the charred remains of the furniture in the ballroom later, they discovered traces of the methylated, spirit and decided that the fire had been brought in to interview hotel staff.

Eventually, three employees were arrested – one charged with lighting the fire, one with assisting him, and the third with supplying the spirit. All three were convicted and given prison terms ranging from 75 to 99 years.

Fire investigators are among the first on the scene after a fire has been put out. Their first task is to preserve and record the remains. Sometimes it is clear that an arsonist has been at work: fires may have been started at several points, or someone might have been spotted running from the scene just before flames were noticed.

The next task is to locate the place or places where it was most intense. The spread of the fire must also be tracked. Much can be learned by looking at smoke patterns and damage to surfaces. Metals and glass can be useful guides. A metal rail will distort or melt according to its proximity to the hottest part of the fire. The density of cracks in glass usually corresponds to the intensity of heat.

Expansion of metals can also be revealing – a steel joist 33ft (10m) long and heated to 932  (500  will expand by 2 ¾ in (70mm). the depth of charring in wood or in layers of carpet also gives an indication of the heat or duration of a fire.

Against this must be balanced factors which help to spread fire. Lift shafts, air vents and stairwells give a chimney effect, raising hot gases to other parts of a building and creating secondary seats of fire. The investigator can be confused by localized fires caused by broken gas pipes or stored fuel. Exploding aerosol cans can create fireballs several feet across.

Having found the seat of the fire, the investigator will look for signs of the cause – empty petrol can leave by an arsonist, charred wiring that indicates a faulty electrical connection, even a fragment of carelessly discarded match.

Forensic scientists are skilled at examining fragments of burnt materials. After one of Italy’s worst fire disasters, the burning of the Statuto Cinema in Turin on February 12, 1983, in which 64 young people died, the projectionist was able to point to the site where the flames first appeared. Fire inspectors discovered the remains of old wiring which had started the blaze.

When remains of the wallpaper, carpeting and upholstery were sent for forensic examination in Rome, scientists found that contrary to Italian fire safety regulations none of these had been fireproofed. After a lengthy trail, the cinema owner, the supervisor of the redecoration work and two local fire officers, who had declared the cinema to be safe, were all sent to prison for between four and eight years.

If no cause of a fire is apparent the investigator might find that a dead body was a murder victim, suggesting the fire was started to cover up the crime. A human body is extremely difficult to burn away completely and the remains can tell investigators a great deal. There could be more intense burning of the body than its surroundings, suggesting that it had been set alight first, or evidence of asphyxiation in the remaining lung tissue, indicating that the person had been strangled.

The fire which killed 31 people at King’s Cross Underground Station in London in November 1987 was first believed by some to be arson. It began on an escalator and was fanned by the draught of air coming from the train tunnels below ground. Investigators finally concluded that it began in accumulated fluff and grease under the escalator, almost certainly ignited by a discarded match. Smoking had been banned on underground trains in July 1984, but many people lit cigarettes on the escalator as they were making their way out of the station.

 

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The lie detector is an assembly of three different instruments. Their outputs are fed separately to the lie detector and recorded as separate traces on a graph.

One instrument, the pneumogram, records breathing patterns. A rubber tube is strapped across the chest, and instruments measure fluctuations in the volume of air inside the tube, which are brought about by variations in breathing.

The second instrument, the cardiosphygnometer, detects variations in the blood pressure and pulse rate. The information is picked up by a bladder and cuff placed over the upper arm, in the way that doctors check blood pressure.

The third instrument is the galvanometer, which monitors the flow of a tiny electric current through the skin. The skin conducts electricity better when it is moist with perspiration. Electrodes are usually taped to the hand.

 

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Medical experts in the USA and Britain say that it is quite possible for a suspected person to beat the lie detector. The trick is to make the responses to the control questions appear as similar as possible to the responses to the real questions. For an answer to be classified as ‘deceptive’, it must register much more strongly than the control answers.

Dr David Thoreson Lykken, professor of psychology and psychiatry at the University of Minnesota Medical School, writes in his book A Tremor in the Blood that the interviewee could identify the control questions during the pre-test interview. He could then do something to increase his response to control questions during the test – something different each time so as not to arouse suspicion.

‘After the first control question, I might suspend breathing for a few seconds, then inhale deeply and sigh. While the second control is being asked, I might bite my tongue hard, breathing rapidly through my nose. During the third control question, I might press my right forearm against the arm of the chair or tighten the gluteus muscles on which I sit. A thumbtack in one’s sock can be used covertly to produce a good reaction on the polygraph.’

Dr Archibald Levey, of Britain’s Medical Research Council, who wrote a report on lie detectors for the British Government in 1988, says that meditation techniques can be used to achieve the opposite effect – by lowering the responses to all questions.

The interviewee could think himself into a relaxed state, concentrating on a different subject or imagining himself to be somewhere else.

 

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In the early 1980s at least a million people every year in the USA were subjected to lie-detector tests – most of them applicants for jobs. However, the tests resulted in some people being falsely accused of dishonesty. One such victim was a college student, Shama Holleman, who was dismissed by a New York department store after a test indicated that she might be a drug dealer and might have served a prison sentence. Both were untrue.

Since then, US companies have been prohibited from using lie-detector tests to screen employees. However, government agencies and some security services and drugs firms are still allowed to use them.

Other major users of lie detectors are police forces, who tests suspects and witnesses in criminal cases, through not in Australia where their use is illegal. More than 60 years after the invention of the lie detector its use remains controversial.

The lie detector works on the assumptions that people who tell a lie become stressed emotionally, and the stress speeds up their pulse and breathing rate, and makes them sweat. These effects can be detected by sensitive instruments.

The first person to use instruments to detect stress through bodily changes was an Italian criminologist, Cesare Lombroso, in the 1890s. He measured variations in pulse rate and blood pressure.

In 1921 the first modern lie detector using continuous monitoring was developed, in conjunction with the local police, by a medical student, John A. Larson, at the University of California, Berkeley.

Larson’s machine recorded simultaneously a person’s blood pressure, pulse rate and a rate of breathing. The results were recorded by three pens making ink traces on a continuous roll of paper. The machine, called a polygraph, was soon dubbed a lie detector.

Later the polygraph evolved into the modern instrument with the addition of a fourth measurement – that of the skin’s ability to conduct electricity, which varies according to the amount of perspiration.

Ideally, lie-detector tests are conducted under strictly controlled conditions. The person to be tested is wired to the machine and asked a series of innocent questions (called control questions), such as: ‘Is your name John Smith?’ (which it may or may not be). This is to elicit a response from the subject that will provide reference traces on the polygraph.

Then if the person lies, the polygraph should be able to detect the changes caused by the stress of lying, and record them.

One drawback is that some people are so nervous that they may appear to lie even though they are telling the truth.

Other people may be so much in control of their emotions that they will be able to lie without affecting their polygraph traces. But this is exceptional.

 

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The objective of a truth drug is to relax, a person’s mind so that he gives completely open and truthful responses to whatever he is asked – even if it means betraying his country.

Research into so-called truth drugs began in earnest during the Korean War in the early 1950s, following reports about ‘brainwashing’ interrogation methods carried out by the North Koreans and Chinese on prisoners of war. The US Air Force began a project to find a ‘truth serum’ so that American pilots could be given it and trained in how to resist brainwashing.

Experiments began with barbiturates, amphetamines, alcohol and heroin, but most of the drugs just helped the subjects to tell lies more skillfully.

Purge trials

Fear of mind-control techniques had been raised during Joseph Stalin’s notorious purge trails in the Soviet Union and the Eastern Bloc countries in the 1930s and 1940s. Defendants appeared in court in an apparently befuddled state, with glazed eyes, admitting to crimes that they could not possibly have committed.

Sodium pentothal, a barbiturate used by anaesthetists to relax hospital patients before surgery, is often described as a truth drug. Its use in this context is to help create a disoriented state in which the subject’s awareness of his surroundings can be manipulated.

The subject is given a strong dose of the drug which makes him unconscious. He is then injected with the stimulant Benzedrine to revive him, but only partially. With the subject in a state of semi-consciousness, a psychiatrist can use hypnotic techniques to change his perception of what is going on around him.

When this method was used on a suspected Soviet spy in West Germany in 1955, his mind was taken back to a stage where he believed he was talking to his wife at home, and he freely gave a detailed account of his undercover activities.

 

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A special form of carbon paper is used as a modern form of invisible ink. A spy lays the carbon paper on another piece of paper and writes his message. His handwriting is transferred invisibly onto the paper underneath, and can only be revealed when treated with a chemical. So it is possible to send messages by post ‘written’ on the pages of, say, women’s magazines.

This method was used by the Czechoslovakian spy Erwin van Haarlem, who in 1989 was jailed for ten years for his espionage activities in Britain. Since 1975 he had sent some 200 secret messages to his spymasters in Prague – many of them in invisible ink. The information included facts about British firms working on American’s Star Wars defence system.

Most chemical invisible inks need a second liquid – known as the reagent – to make them visible. One of the most popular inks is copper sulphate diluted with water. When the paper is later immersed in a weak solution of sodium carbonate (washing soda) and water, or ammonia and water, the writing appears blue.

A particularly sensitive chemical ink used by German spies during the Second World War involved chemicals used in photography. The ink was a solution of lead nitrate and water. The reagent was a small amount of sodium sulphide in water. It produces a shiny black print.

It was a crystal of concentrated invisible ink chemical, concealed in a hollow key that led a Second World War German spy, Oswald Job, to the scaffold. The ingenious hiding place was discovered when job was searched, and it led to his confession and execution in 1944.

 

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In the modern era of bugging, no conversation in office or home is safe from eavesdroppers. The bugging is usually done by smuggling a small but sensitive microphone into the room.

One type of bug uses a low-powered radio transmitter attached to the microphone to send its signals to a receiver a few yards away. Another type has the microphone connected to a receiver by a cable.

Although a wired-in system requires careful concealment of the cable, it has the advantage of not broadcasting a radio signal, which is easy to detect. And most rooms or offices have so much cable already installed that the extra wire goes unnoticed. The microphone can be designed to resemble a household appliance, like a light bulb, television or telephone.

Provided a listening post can be found within a reasonable radius of up to a kilometre and a half, every word spoken in the target room will be relayed over the wire. An existing cable, such as a spare telephone line, is usually used to carry the voices.

One of the reasons why diplomatic buildings are so closely guarded when under construction is the fear that a foreign intelligence agency might try to incorporated cable conduits into the fabric of the building. This occurred in Moscow in 1987, where all the steel beams delivered to the site of the Us Embassy were discovered to be hollow.

If an eavesdropper cannot gain access to a room, he can put a bug called a stethoscope to one of the walls from the outside. It is a simple microphone pressed to the wall, and rigged to an amplifier. Alternatively, a hole can be drilled through the wall from the outside, ending as a tiny pinhole on the inside of the room. A microphone in a tube is placed in the hole and connected to a tape recorder outside. A variation is the ‘spike’ which penetrates only part of the wall, but nevertheless picks up all the sounds in a room.

Inserting a device into a target room can be difficult if the room’s occupants know they may be spied on. So the laser has been exploited to help the eavesdroppers. A laser beam is focused on the window of the room. When a conversation takes place inside the room the glass in the window vibrates to the voice waves, and the microscopic movements of the glass can be detected by measuring the tiny variations in the length of the fixed laser beam. This information can then be converted back electronically into an intelligible form.

The cavity microphone is probably the ideal cordless device, requiring neither batteries nor maintenance. It consists of a capsule, about 1in (25mm) wide, containing a sensitive aerial and a diaphragm (a thin disc). When a radio beam is directed at the room from outside, the capsule is transformed into a radio transmitter that picks up sounds in the room, allowing any conversation to be overhead.

One of these bugs was found in a model of the American Great Seal that had been presented to the US Ambassador by the Mayor of Moscow in 1952 and had hung over his desk for years.

 

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In November 1979, the British Prime Minister Margaret Thatcher announced to the House of Commons that one of the most respected men in the British art world, Sir Anthony Blunt, Surveyor of the Queen’s Pictures, had been working as a spy for the Russians.

Blunt had become a Communist in the 1930s and had worked for the British Security Service (MI5) during the Second World War, passing secrets to Moscow. In 1951 he helped two other British spies, Guy Burgess and Donald Maclean, to flee to Russia when they came under suspicion.

Blunt was an example of the type of spy known as a ‘mole’ – agents who are prepared to wait for years, building up their cover, until they get access to vital information.

Unlike more conventional spies who are recruited by their own country to undertake a mission in another, the mole is often someone who, usually for ideological reasons, has chosen to work for an alien cause. Having taken that decision, he deliberately manoeuvres himself into a position where he can inflict the most harm. And all the while he plays the part of a patriot.

Some moles are recruited by intelligence specialists known as case officers. Others recruit themselves by volunteering their services.

Probably the most renowned case since the Second World War was that of the four British spies Blunt, Burgess, Maclean and Kim Philby. All decided, while still at Cambridge University in the 1930s, to work secretly for the Soviet Union.

They were initially recommended by ‘talent-spotters’ who passed each onto a Soviet case officer who taught them the rudiments of espionage, and told them to give up their memberships of radical political groups. They were to make themselves as attractive as possible to official organizations.

Each man deliberately cultivated people in positions of influence whom he believed might assist him to find a useful job. Eventually Burgess and Maclean joined the Foreign Office, Philby the Secret Intelligence Service (MI6), and Blunt the counter-espionage service, MI5.

Once they were in their target organizations, the four men progressed to the most sensitive levels of government, gaining access to the most damaging information.

Maclean, Burgers and Philby all fled to Moscow and eventually died there. Blunt made a full confession to the British Security Service and was not prosecuted. He died in 1983.

A mole who spied against his own country purely for the money was Heinz Felfe, a former officer in the German SS who rose to an eminent position in the West German Federal Intelligence Agency in the 1950s.

In 1951, while looking for a job, he agreed to work for the Soviet secret service (later the KGB), for a salary of 1500 marks a month. At the same time he joined the Federal Intelligence Agency. For the next decade he worked as a double agent, feeding ‘disinformation’ about the KGB to the Germans and in return sending the KGB highly damaging information about the German spy network behind the Iron Curtain.

Suspicious about him finally arose when he bought a house which was too expensive for a man or one salary. When he was arrested in 1961 it was discovered that his activities had lost the West Germans 94 contacts behind the Iron Curtain, including 46 active agents. In 1963 Felfe was sent to prison for 14 years.

Another turncoat spy – who operated in the USA from the late 1960s to the mid-1980s – was John Walker, a former naval officer. His Russian spymasters paid him $1000 a week to run a family espionage ring, consisting of his brother Arthur, a retired Navy lieutenant commander, and son Michael, a seaman abroad the aircraft carrier USS Nimitz. Their activities enabled the Soviets to decipher countless top-secret communications and receive more than 1500 secret documents.

A quite different type of mole is the ‘sleeper’ who enters a foreign country on false documentation and burrows deep into the fabric of his adopted society.

Peter and Helen Kroger, US citizens of Polish extraction, were just a couple. Outwardly he was an antiquarian bookseller who, with his wife, led a comfortable suburban life at Ruislip in west London in 1961. In reality, the Krogers operated an illicit KGB wireless link with Moscow until they were arrested.

When the Kroger house was searched, even the most innocent-looking household item was revealed to be part of the paraphernalia of espionage. An apparently ordinary tin of talcum powder contained compartments for storing microfilms and a microfilm reader like a tiny telescope.

Renate and Lothar Lutze were deep-cover East German moles operating in West Germany before being arrested.

Born in Brandenburg, East Germany, in 1940, Renate Ubelacker, as she then was, got a job as a secretary in the West German Ministry of Defence in Bonn. Her work involved handling top-secret documents – including those dealing with NATO plans. In September 1972 she married Lothar Lutze, then a spy for the Ministry for State Security in East Germany. She succeeded in getting him a clerical job in the Defence Ministry.

For the next four years the couple gave vital information to the Russian-controlled East Germans. They were unmasked and arrested in June 1976. After spending three years on remand, Renate Lutze received a six-year sentence for spying and her husband was jailed for 12 years. She was released from prison in September 1981.

The most effective moles are those who are the very last to fall under suspicion. Burgess had been educated at Eton; Maclean’s father had been a Cabinet minister; Philby had joined SIS from The Times, and at the time of his exposure Anthony Blunt had been appointed Surveyor of the Queen’s Pictures at Buckingham Palace and had been knighted.

Some moles can be given a period of training before going into the field. For their own security it is vital for the moles to learn about secret methods of communicating with their own side and ways of spotting whether they are being watched.

The CIA operates a large base disguised as a military establishment at Camp Peary, in Virginia, USA; the French maintain a remote school high in the Alpes Maritimes in south-eastern France; while the Russian KGB have training centres near Leningrad.

However, it is occasionally impossible for a mole to undergo training, and he may have to be taught basic techniques while actually operating.

Oleg Penkovsky, a Russian lieutenant colonel, volunteered his services as a spy to the British in 1960. When he made a rare visit to the West in a Soviet trade delegation the following year, he was shown how to use a miniature camera and briefed on cipher systems. Instead of slipping away from his group, he simple pretended to go to bed early at his London hotel. In fact the British and Americans had hired the entire floor of the hotel directly above his room, and installed all the equipment necessary for the training sessions. The arrangement worked perfectly, and by the time he was due to return to Moscow Penkovsky was a fully fledged agent.

But his spying career was short-lived. Penkovsky was arrested by the KGB the following year and sentenced to death.

 

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On the eve of the Japanese attack on Pearl Harbor in December 1941, an apparently innocent weather forecast, ‘East wind rain, north wind cloudy, west wind clear’, alerted Japanese diplomats around the world that war was imminent.

The message is one of the simplest forms of code – a prearranged message which had a special meaning to those who received it.

Similar messages were broadcast by the BBC during the Second World War to the French Resistance. A sentence such as ‘Romeo embraces Juliet’ or ‘Benedictine is a sweet liqueur’ might convey prearranged information about the dropping of agents or supplies. The first line of a poem by the French writer Paul Verlaine (‘The long sobs of the violins of autumn’) told the Resistance that the D-Day landings were about to begin.

More complex codes replace words or whole phrases with other words or phrases. Alternatively, groups of unconnected letters may be used to create a whole dictionary of words and phrases. For example, the order ‘Provide supporting fire’ might be conveyed by the letters GYPHC. Long military reports can be transmitted in these five-letter groups – only intelligible to someone who can look them up in the correct codebook.

If a codebook falls into enemy hands, however, vital information can be intercepted without the sender’s knowledge. In the First World War the German naval codebook was recovered from the wreck of the light cruiser Magdeburg. Consequently many of the German High Seas Fleet’s most sensitive orders were read by the British. Even when the German Admiralty discovered its loss, it took weeks before it could supply every German ship with a new codebook.

The other major method of sending secret information is with ciphers. A cipher substitutes letters, numbers or symbols for the real letters of the alphabet. The Morse code is actually a cipher, conveying each letter by combinations of short and long signals which can be sent by radio bleeps, telegraph or signal lamps. The letter E, for example, is a single dot, while Q is dash, dash, dot, dash (- - . -).

Another common, and simple, form of cipher is worked out on a grid called a cipher box. The message ‘Enemy troops embark December first’ could be written in a grid of, say, six columns, alternately writing left to right and right to left.

The person who receives the message uses a similar grid to decipher it.

A weakness of the system is that the frequency of letters and combinations of letters remains the same as in normal language. E, for example, is the most commonly used letter in the English language, and Z is one of the least common. The combinations EE and OO occur frequently. Someone trying to break the cipher can assume the most-often occurring letter represents E, and so on.

So immensely complicated ciphers, involving numbers as well as letters, have been developed by mathematicians.

During the Second World War the German government used a cipher machine called Enigma. However often a particular letter was keyed, it would never repeat the same cipher letter. Each day a new basic setting was made, according to a schedule known only to the Germans.

A team of university mathematicians and linguists in Britain eventually unraveled Enigma’s ciphers in 1940. Their work played a major part in winning the war by giving Allied Headquarters an up-to-the-minute picture of the German plans in the North African campaign and the air war.

With the advent of computers, codes have become far more complicated and difficult to break. Complex programs use thousands of calculations, and without knowing the sequence of key commands, they could take thousands of years to decode.

 

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When a government official wants to make a confidential telephone call to, say, an embassy abroad he uses a voice scrambler. As the conversation travels between the two telephones it is nothing but incomprehensible noise to anyone ‘trapping’ into the line.

Most scramblers are electronic ciphering machines that invert the high and low tones of a human voice to make it unintelligible. Other scramblers conceal the voice in a background of continuous noise.

At one time scramblers were issued only to senior military commanders who had to exchange sensitive information over telephone lines that might be listened into by the enemy. Now scramblers have become more easily available, and are often used by international businessmen anxious to protect trade secrets from unscrupulous competitors. Modern technology has reduced their size so they fit into a briefcase.

Double unit

Scrambling requires two units, the transmitter and the receiver. The transmitter converts the caller’s speech into the unintelligible form and sends it down a normal telephone line. The receiver reverses the process so that the voice can be understood at the other end. Eavesdroppers tapping into the line will hear a highly distorted, synthetic noise that is hardly recognizable as human speech.

Most scramblers work by splitting the sound of the voice into five frequency bands which are then mixed through a complicated electronic process which moves and inverts them. In theory there are about 3840 possible combinations, but standard scramblers use 512 permutations.

Voice scramblers are not a complete safeguard against skilled eavesdroppers, as conversations can eventually be unscrambled. But the process is extremely time-consuming, requiring the use of specially programmed data processors and highly trained operators, so scramblers do give short-term protection.

In the early 1960s, the US Embassy in Moscow managed to pick up the scrambled conversations passing between the Politburo’s fleet of limousines. Although there was a long delay before the signals could be unscrambled, the exchanges contained some extremely useful political information – and quite a bit of Kremlin gossip. The operation eventually ended when new security measures were introduced.

 

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During the American War of Independence in the late 18th century some British units took to wearing buckskins in place of their traditional red coats. The men found that red made a good target for the American riflemen, whereas the dun-coloured buckskin was not so readily visible.

The use of such camouflage was taken further during the Afghan War in 1880. A colour known as khaki (the Urdu word for ‘dust’) was generally adopted to make the soldiers’ movements less obvious to the natives. Veterans who had served in India – and who had stained their white helmets brown with tea – knew that lack of visibility was the key to their survival in wartime.

During the Boer War of 1899-1902, however, British troops were still wearing bright scarlet uniforms. They had been traditional since the English Civil War, 250 years earlier, when Parliamentarian soldiers were provided with red coats simply because a large amount of red cloth was made the British soldiers easy targets for the Boer riflemen.

When the First World War broke out in 1914, dull colours such as khaki and grey had become the standard colour for uniforms, enabling soldiers from both sided to blend in with their combat surroundings.

Even so, the use of spotter planes left troops dangerously exposed on the ground. Camouflage netting and the ‘dazzle painting’ of weapons in zebra stripes was gradually introduced.

During some military manoeuvres on Salisbury Plain, the commander of a British army division – a survivor of the Boer War – told his men to attach pieces of foliage to their helmets, conceal their vehicles with drab netting and take advantage of the natural cover to hide themselves from aircraft.

The ruse was so successful that the division indistinguishable from the surrounding countryside. The idea of an entire unit losing itself in the landscape grew so attractive to the military command that camouflage gradually became accepted as an important weapon in the modern arsenal.

During the Second World War, camouflage was widely used as a technique of deception. As in the First World War, vulnerable installations such as fuel depots and munition stores were covered with netting so, from the air at least, they merged with the background. Decoys were deliberately displayed close by to draw enemy fire. Conspicuous area of water like the canals, used by bomber navigators as landmarks at night, were sprayed with coal dust to prevent them reflecting moonlight.

During the North African campaign of 1940-3 a dummy railway line was constructed to resemble a new supply spur to a tank assembly point. It even carried a fake train, complete with freight wagons and flat cars, and an impressive-looking locomotive with a disused camp stove billowing smoke from a cardboard funnel.

The hoax diverted attention away from the genuine rail head which was used to support General Auchinleck’s offensive against Tobruk in November 1941. His main forces and fuel dumps were so well hidden that the enemy never found them.

Camouflage has also been used to reduce the visibility of aircraft and ships.

When the underside of a bomber is painted light blue, it merges with the daytime sky, and when painted black, with the night sky. Some planes are painted on top so that – when seen from above – they merge with the ground below. Similarly, the familiar outline of a warship can be distorted by skillful paintwork designed to reduce the silhouette and even give the impression of a less threatening outline, perhaps that of an unarmed merchantman.

A false bow wave painted onto the hull of a warship can mislead a submarine captain about the speed of his target, and a false water line can confuse the range.

Camouflage techniques have been used to deceive air reconnaissance. During the Falklands campaign in 1982, British commanders were advised that the beleaguered Argentine forces could not be resupplied because Port Stanley’s only airfield was serviceable, having been damaged by the RAF’s bombs. Reconnaissance pictures showed what appeared to be a deep crater across the main runway.

In reality, heavily laden Argentine planes flew in every night, under cover of darkness, right up to the day before the surrender. It was only discovered much later that each morning a group of raw conscripts – equipped with nothing more than buckets, spades and wheelbarrows – left a circular pile of earth on the runway. When viewed from a height, their handiwork resembled a bomb crater.

 

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In the late 1950s the American Central Intelligence Agency began sending Lockheed U-2 ‘spy-planes’ over the Soviet Union to take intelligence photographs. The U-2s flew at 80,000ft (24,000m) to be out of range of anti-aircraft fire, but it became clear that radar was not detecting them.

These extraordinary planes were little more than jet-powered gliders built of plastic and plywood. On takeoff they jettisoned their small outrigger wheels from the ends of their wings – and they landed on their main, retractable wheels in the centre.

It was not until May 1960, after more than four years of overflights, that the Russians shot one down using new radar equipment belonging to SA-2 surface-to-air missiles. And even then the U-2 did not receive a direct hit. A missile exploded close enough to put the fragile aircraft into an uncontrolled diver, and the pilot, Gary Powers, had to eject.

The success of the U-2s led to highly classified research work in the United States, known as ‘Stealth’, to create a military aircraft that was invisible to radar.

The U-2 had gone undetected for so long because it was made of non-metallic materials which absorbed radar waves rather than reflecting them back to the radar ground station as normally happens.

The Stealth programme aimed at designing high-performance military aircraft incorporating, among other features, a minimum of metal and with the exterior clad in highly absorbent tiles. The aircraft would be almost invisible to radar and could make most radar-controlled anti-aircraft systems obsolete.

Key targets

After being developed under a blanket of secrecy, the high-tech B-2 Stealth bomber was unveiled at the Northrop Company’s manufacturing plant in Palmdale, California, in November 1988.

An audience of invited guests and journalist was kept well away from the plane – which is designed to slip through enemy radar defences without being detected and then drop up to 16 nuclear bombs on key targets.

To help achieve radar invisibility, the bomber is coated with radar-absorbent paint on its leading edge.

A similar technology of radar invisibility is used underwater to foil sonar detection. Modern submarines are coated in a thick layer of a top-secret resin which is highly absorbent acoustically, and reflects only a minute amount of the energy transmitted by sonar detectors.

Ground clutter

Another technique used by aircraft to avoid radar is to fly at very low levels where there is a great deal of ‘ground clutter’ – radar reflections given off by buildings and other objects. Low-level aircraft can go undetected by most radar systems. But the latest, most sophisticated ground-defence systems are designed to discriminate between ground clutter and hostile planes. In addition, ground clutter is partly avoided by using ‘look-down’ radar systems, which track aircraft from other aircraft flying above.

 

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