Like hell it has. How many times did they have to waterboard SKM? 183 times? That tells me it doesn't work for shit. If it was proven to work, they shouldn't have had to do it more than once or twice. the fact is that the FBI got all the actionable intel from SKM in a mattter of hours, and once the waterboarding started, they got nothing from him but false confessions.
In the "real world," going back to the Spanish Inquisition, waterboarding has been considered torture. Was Torquemada looking for intel? No, he was looking for confession of sins, after which the sinner would be burned at the stake. but the copmfssion hadf to be "pure" and not the ramblings of a mortally wounded prisoner, so he preferred the "water cure" as he referrred to it, because it left no wounds, mandated that no more than 8 quarts be used, and that a physician be present to ensure the confession was "pure." Tomas de Torquemada was a mass murderer considered by historians to be on the same level as Hitler and Stalin. Do you really want to defend the use of a torture technique favored by one of the most heartless and cruel religious fanatics in history as an "enhanced interrogation technique" when all the evidence and history says otherwise?
Here's some more history, but a lot more current and involving the US of A: after WWII, the US government prosecuted, convicted and HANGED two Japanese officers as war criminals for waterboarding American and Australian prisoners, and no defense of "we were only interrogating them" was accepted. We gave them "a nice, fair trial and a damn fine hangin'," to paraphrase Judge Roy Bean, in a somewhat different set of circumstances (that's what he told some accused cattle rustlers before their trial. Oopsie. Unfortunately for the rustlers, there was no time for appeal. Bummer, dudes.)
The attermpted defense of torture as interrogation techniques is not only morally abhorrent, but ignorant, showing several things about the would-be defender: not the least of which is the "moral relativism" so often decried by the right when they think they perceive it in the left, just one more example of the ethical hypocrisy inherent in the right, whose favorite worldview is that their end justifies their means, because their hearts are "pure" (where did we just hear that?). but their adversaries are evil, so their means are criminal, but it's okay to use their means on them, and they're not criminal when we use them, becsause we are God's chosen (excerpt that's exactly what every other fanatic slimeball says, including Islamic terrorists and Hitler and Torquemada. But guess what? In th eresl; world, you are judged by your actions, and you don't get credit for being less of an asshole than the other guy. If you do something assholish and barbaric to your dversary, you're swtill a barbaric asshole,and it doesn't matter that he did it to you first and/or worse. If you perform the act of a mass-murdering barbarian, you are no better than as mass murdering barbarian, regardless of what he did to you.