The Senate Armed Services Committee has a report on torture today that's filled with revelations. I haven't read it yet, but the Washington Post's report says:

1. The military derived its torture techniques from Chinese and North Koreans:

The techniques, including waterboarding, or simulated drowning, were drawn from the methods used by Chinese Communists to coerce confessions from U.S. soldiers during the Korean War -- a lineage that one instructor appeared to readily acknowledge.

2. The Pentagon turned to torture in part because interrogations were not producing sufficient evidence of the (largely fictitious) link between Iraq and al-Qaeda:

By late 2001, counterterrorism officials were becoming frustrated by the paucity of useful leads coming from interrogations -- a meager showing that was linked, according to one Army major, to interrogators' insistence on "establishing a link between al-Qaeda and Iraq," the report said. 

3. Some members of the military immediately recognized the legal and moral problems involved with torture, but were overruled:

One Army lieutenant colonel who reviewed the program warned in 2002 that coercion "usually decreases the reliability of the information because the person will say whatever he believes will stop the pain," according to the Senate report. A second official, briefed on plans to use aggressive techniques on detainees, was quoted the same year as asking: "Wouldn't that be illegal?"

--Jonathan Chait