Cheap, simple, and horribly effective, waterboarding dates back at least to the Spanish Inquisition as a way of extracting information by instilling extreme fear and pain without leaving visible marks.

The torture has come by many names — “tormenta de toca” to the Spanish Inquisitors, “showering” in 19th-century prisons, and “water cure” in the 20th century — and has taken many forms.

The technique, however, has hardly varied in the past 500 years. Its intention is to simulate slow drowning and terrify the victim into a confession.

In most instances, water is poured over the face and into the breathing passages, usually on to a cloth or plastic wrapping, causing the victim to feel that they are on the point of suffocation and death.

Torturers at the time of the Spanish Inquisition, in search of heretics, were particularly keen on using the toca — referring to the cloth placed over the victim’s mouth — with its echoes of Christian baptism.

Agents of the Dutch East India Company used a variation of waterboarding during the Amboyna Massacre of 1623 when twenty people, including ten employed by the British East India Company, were tortured and murdered.

In that case the torturers “poured the water softly upon his head until the cloth was full, up to the mouth and nostrils, and somewhat higher, so that he could not draw breath but he must suck in all the water”. The case prompted outrage in Britain.

Many of the world’s nastiest regimes have resorted to waterboarding, including the Gestapo and Kempeitai (the Japanese military police) during the Second World War, the Khmer Rouge, and the Pinochet regime, where the method was known, with grim euphemism, as “Asian torture”.

One waterboard used under Pol Pot, a flat board on which the victim was strapped, remains on display at the genocide museum in Cambodia. But the use of waterboarding is by no means restricted to rogue regimes.

The practice was technically illegal during the Vietnam War, but in 1968 The Washington Post ran a photograph of an American soldier taking part in the waterboarding of a captured Vietcong fighter, and described the technique as “fairly common”. The image led to a military investigation and the soldier was court-martialled and dismissed.

The technique of “slow motion drowning” inflicts intense mental and physical suffering, and can cause severe long-term damage to the lungs and brain, but it leaves no obvious physical marks on the body. As well as being deniable, this form of torture may be inflicted repeatedly.

There is also no doubt that waterboarding works, to the extent that it producing confessions. Whether the information extracted is of any value is more doubtful. A person on the point of drowning may tell the truth, or simply what he thinks the torturer wants to hear to stop the ordeal.

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