Forms of waterboarding vary but generally consist of immobilizing an individual on his or her back - head inclined downward - and pouring water over the face to induce the sensation of drowning.
Other techniques include dunking prisoners head-first into water, as was used by Chadian military forces in the mid 1980s. The Khmer Rouge, responsible for the deaths of approximately 1.5 million Cambodians during the 1970s, strapped victims on inclined boards, with feet raised and head lowered, and covered their faces with cloth or cellophane. Water then was poured over their mouths to stimulate drowning.
Waterboarding, long considered a form of torture by the United States, produces a gag reflex and makes the victim believe death is imminent. The technique leaves no visible physical damage.
Republican presidential candidate John McCain, who was tortured as a prisoner of war in North Vietnam, considers waterboarding a form of torture. McCain has been quoted as saying that waterboarding is "no different than holding a pistol to his head and firing a blank."
After World War II, U.S. military commissions prosecuted several Japanese soldiers for subjecting U.S. soldiers to waterboarding, according to Human Rights Watch. In 1968, a U.S. soldier was court-martialed for water boarding a Vietnamese prisoner.
But in October 2006, Vice President Dick Cheney confirmed the United States had used the controversial technique to interrogate senior Al Qaeda suspects, and he said the White House did not consider waterboarding a form of torture.
In the aftermath of September 11, fewer than 100 terrorists have been held in the CIA's secret prisons, and fewer than one third of those have been subjected to what CIA Director Michael Hayden calls "special methods of interrogation," and what others called torture.
"The intelligence they produce is absolutely irreplaceable," Hayden said. "It's been crucial in giving us a better understanding of the enemy we face as well as leads on taking in taking other terrorists off the battlefield."
The CIA says it no longer uses waterboarding.
Cheney confirmed waterboarding was used to interrogate Khaled Sheikh Mohammed, the senior Al Qaeda operative now being held in Guantanamo Bay, adding that the use of the technique was "a no-brainer."
"The Bush administration continues to astonish," said Larry Cox, Amnesty International USA's executive director. "Its own State Department has labeled water boarding torture when it applies to other countries. Yet in President Bush's legal wonderland, water boarding is renamed an enhanced interrogation technique. President Bush continues to assert that his administration is complying with U.S. and international law, yet every available fact has proven the contrary."