Why did proponents of the torture memo believe that waterboarding was an acceptable interrogation technique?

Central Intelligence Agency (CIA) was using waterboarding on extrajudicial prisoners and that the Office of Legal Counsel, Department of Justice had authorized the procedure among enhanced interrogation techniques. Senator John McCain noted that in World War II, the United States military hanged Japanese soldiers for waterboarding American prisoners of war. The CIA confirmed having used waterboarding on three Al-Qaeda suspects: Abu Zubaydah, Khalid Sheikh Mohammed, and Abd al-Rahim al-Nashiri, in 2002 and 2003.
 In its war on terror, the George W. Bush administration through Jay S. Bybee, the Office of Legal Counsel, Department of Justice, issued in August 2002 and March 2003 what became known in 2004, after being leaked, as the Torture Memos. These legal opinions (including the 2002 Bybee memo) argued for a narrow definition of torture under U.S. law.

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