Some obvious tortures require highly specialised equipment. In medieval times, the Iron Maiden of Nuremburg was used to kill victims slowly and painfully. The device was a coffin-like box which stood vertically and was fitted inside with numerous spikes. The victim was placed inside the Maiden, and it was then closed. Closing, it forced the spikes into the victim’s body, but not far enough to be immediately fatal. The victim, impaled in dozens of places, would slowly bleed to death, with every dying twitch adding to the accumulated agony. The rack in its original form was a platform with rollers at each end. Cords around the rollers were tied to the ankles and wrists of the victim. The rollers were slowly ratcheted around, stretching the victim until eventually the major joints pulled apart. Inexperienced or malevolent operators might pull the limbs off entirely. In the early history of settlement at Botany Bay, troops used the cat-o’-nine-tails to win obedience and respect. It was a whip with nine leather thongs; each thong was beaded with small pieces of lead. It strips the victim to the bone very quickly. The navy had used it for a long time. The Russian version has hooks on the end of each strap, the better to tear the flesh away.

Torture has two main purposes. The first is to inspire general terror and thereby induce obedience and respect for the law and the government. To achieve this purpose, the torture must leave obvious marks. Flaying, piercing, crippling and branding were considered useful in this endeavour, and examples abound. In the early days of the American colonies, branding was popular. For example, convicts were branded with initials to signify the nature of their crime: SS for slave stealers, B for blasphemers, and so on. They were branded on the hand so that their infamy would be clear when they raised their hand on taking an oath – a practice which still survives in American courts.

Although torture has been used for this purpose in most countries at some time in their history, the results have not been good. Across the ages, the use of obvious torture to inspire obedience and respect seems to have been a failure.

Nowadays, torture is generally thought to be repugnant, and it is banned by the Torture Convention. This idea under-pins the major theme of Rejali’s book. It is this: since torture is wrong, but we feel impelled to use it, then it must be done by stealth.

Rejali makes out a powerful case to show that stealthy torture is used by virtually every country in the world. In 2000 a Cambodian policeman said to his victim: ‘This won’t leave marks; no one will believe you.’ That is the guiding philosophy of modern torturers. It reveals a profoundly important truth: we condemn torture but we use it, so it must be plausibly deniable. There is an important variation of this response: we condemn torture but redefine its meaning so we can continue to practise it. This is a method recently favoured by the Americans.

Instruments like the Iron Maiden, the rack and the cat-o’-nine-tails have a small disadvantage for modern users: they are designed for a specific purpose, and the purpose is unmistakable. For stealthy torture, the equipment needed must be apparently benign or demonstrably suitable for legitimate purposes.

Whether torture is obvious or stealthy, the second main reason for using it is to acquire information. The need for information is sometimes urgent, sometimes not. When the need is urgent – the ticking bomb hypothesis – some commentators are tempted to urge the legitimacy of torture. Just when it seemed possible that human rights were being taken seriously, the attack on the United States happened. It is in this context, in the ‘post 9/11 world’, that the discussion of torture has re-emerged, like some vanquished beast climbing out of its crypt. Some advocates now openly embrace the possibility of authorising torture as part of the ‘war on terror’. Since many embraces spring more from desire than from understanding, condoning torture to extract information urgently has no rational justification. There is virtually no empirical evidence that torture extracts reliable information. Rejali takes trouble to analyse documented cases of torture for information (French Algeria in the 1950s, Northern Ireland in the 1970s, Iraq and Guantanamo recently) and demonstrates that, generally, the quality of information was lower than that obtained by orthodox, lawful police methods. This is intuitively true: most of us would say whatever was necessary in order to bring an end to the pain. This is why courts refuse to admit confessional evidence extracted by force.

Nevertheless, with a devotion which is quite touching, the ticking bomb theorists cheerfully advocate torture without calculating the cost or the benefit. At the same time, they claim a sort of decency because they reject the idea of obvious torture, the sort that leaves embarrassing marks or mutilation. Rather, they promote ‘clean’ torture. This was the approach adopted in the United States Department of Justice, when they gave the nod to forms of torture which fell short of causing organ failure or death. Western democracies are a bit squeamish when it comes to obvious torture. Other countries have progressively shifted their focus away from obvious torture to ‘clean’ torture, not because of any new-found sensitivity but because human rights NGOs are everywhere on the lookout for bad practices, and foreign aid can be adversely influenced by a bad report.

It is surprising, and disturbing, to learn how much pain can be inflicted without leaving permanent marks. Plausibly deniable torture is simple. Rejali deals with all of the techniques, and identifies the styles of torture preferred by various modern democracies. The main forms of stealthy torture fall into the following categories: electrotorture; beating; water torture; dry choking; air; exhaustion exercises; positional tortures; positional devices; restraints; drugs and irritants; sleep deprivation; and noise. Each category contains a number of distinct tortures. Rejali deals with each category, and each form of torture in each category, with painful clarity.

It is disturbing to be reminded of the forms of ‘clean’ torture which have been practised during the six decades since the Universal Declaration of Human Rights in 1948, and which are still being used. Some forms are less obvious than others. The category ‘positional devices’ includes ‘wet sheeting’. The victim’s head is wrapped tightly in a wet sheet. As the sheet dries it tightens and compresses the head painfully. ‘Clean beating’ includes obvious things like beating with sandbags or rubber hoses, but it also includes a method used during the Vietnam war: the victim stands in a deep barrel of water, the torturer beats the sides of the barrel with a mallet, and before long the victim begins bleeding from the mouth, eyes and ears.

Positional tortures are very widespread. The technique sounds innocent enough: the victim is forced to remain fixed in a single position – standing, crouching or squatting. After a few hours, the pain is excruciating. Prolonged standing causes the limbs to swell to double their normal size. It is a matter of record that prisoners in Guantanamo Bay were forced to remain squatting for up to eighteen hours at a time. A victim forced to remain in a single position for many hours will be crippled for days afterwards, but the damage is not permanent.

Waterboarding has several forms. In its original form, the victim is strapped to a board and lowered headfirst into a tank of water. He is pulled out and drained just as he starts to drown. In a variation of this, the face of the immobilised victim is wrapped in cloth and water is poured continuously onto the cloth so that each breath takes water into the stomach and the lungs. In either case, the physiological need to breathe rapidly induces abject panic and terrible pain. Other water tortures include forcing water into the stomach of the victim until the stomach is distended to its limits, and then the victim is pressed or jumped on, expelling water from the mouth and the anus.

Dry choking involves drawing a plastic bag over the victim’s head and tying it around the neck. It is removed shortly before the victim asphyxiates. Variations include placing a gas mask over the victim’s face and shutting off the vent in the mask.

By far the most popular mode of ‘clean’ torture however is electrotorture. A suitably calibrated electric shock is devastatingly painful and physically disabling, because it causes all affected muscles to contract to their physical limits. Use of electrotorture spread quickly in the military because field communications used telephones powered by a magneto. A magneto is a small, hand-operated device which rotates a coil in a fixed magnetic field and thereby generates electricity. The same technique was previously used to power the lights on bicycles.

A magneto can produce an electric current powerful enough to be extremely painful, but not lethal. Torturers the world over have adopted electrotorture as a favoured method. The magneto is less common now than formerly, but modern torturers have a wide range of electrotorture methods to choose from. Law enforcement agencies have created a market for electrical devices for subduing suspects. In the full spectrum of police methods, stun guns and Tasers have their proper place. However, their availability as legitimate devices creates a real risk that they will be used for wrong purposes. Because stun guns and Tasers are products with a legitimate market, they are readily available, and their manufacturers are not particular about the identity of their customers. To the contrary, they are very active in generating and expanding the market for their products.

Seventeenth-century torture was characterised by the rack: the twenty-first century will be characterised by electrotorture. The enduring image of Abu Ghraib was that of the hooded man with wires attached to his hands. The world instantly recognised that a prisoner was being tortured with electricity. What was interesting about the Abu Ghraib revelations was the reaction of generals and politicians, who professed their horror and distaste that such things should occur. But they knew it already. Abu Ghraib was just another example of stealthy torture. The Americans have used stealthy torture for decades. It is a matter of record that prisoners in Guantanamo had been subjected to stealthy torture from the outset.

What was shocking about the photographs from Abu Ghraib was that they became public. In an age of ‘clean’ torture, publicity is as bad as the disfigurement caused by obvious torture. The Americans, caught between a belief that clean torture is effective and a wish to promote the ideals of freedom and justice, have tried to redefine torture in order to make their existing methods acceptable. What has been officially (but secretly) authorised at Guantanamo is far worse than what was shown in most of the Abu Ghraib photographs. The official horror at the Abu Ghraib photographs was not about decency, it was about publicity. Modern torture is secret and deniable. Abu Ghraib broke that cardinal rule.

Rejali’s book is tough reading. It takes you into dark territory, from which you cannot emerge unchanged. The sad truth is that torture may be a way for the angry or inarticulate to vent their rage about the world, but it is not effective as a means of gathering reliable intelligence. It is easier to understand the mind of the torturer, whose anger or sadism finds an outlet in torture, than it is to understand the politicians and generals who outwardly condemn torture while secretly condoning its use.