“The resulting occlusion,” the directive said, “was primarily from water filling the nasopharynx, breathholding, and much less frequently the oropharynx being filled — rather than the ‘sealing’ effect of the saturated cloth.” The drowning experience, in other words, wasn’t simulated; it was real.

That C.I.A. interrogators actually employed this method is consistent with videotapes of waterboarding sessions. A 2004 review of these since-destroyed videos found that instead of using the wet-cloth technique, interrogators “continuously applied large volumes of water.” The review, by the C.I.A.’s inspector general, noted that this “differed” from what the Justice Department had authorized. The agency’s method, a psychologist-interrogator told the inspector general, was “more poignant and convincing.”

The medical service instructed physicians to manage waterboarding’s dangers by combining the practice with sleep deprivation and shackling of detainees in stressful positions; this, the service advised, could “prolong the period of moderate use of the waterboard by reducing the intensity of its early use.”

The service conceded in the recently released text that the abuse its doctors helped to plan put detainees at deadly risk. Inhalation of water, spasm of the larynx, hypothermia and lung and limb infections are among the hazards physicians were told to watch for.

The role of physicians included assessing the comparative efficacy of abusive methods. The medical service judged extended sleep deprivation “most effective” because of its “demonstrably cumulative” contribution toward “demonstrating helplessness in an unpleasant environment.” But it concluded that confinement in tiny boxes worked poorly since this offered “a respite from interrogation,” and it expressed skepticism about the effectiveness of waterboarding.

Some of the agency’s doctors challenged the torture program’s efficacy and questioned why the psychologists who created it served in conflicting roles as both its managers and evaluators. There were objections, as well, to the ethics of putting behavioral science to such brutal use. But the program’s advocates prevailed, and the medical service instructed its physicians accordingly. There have been no public indications that any refused to go along.