After the September 11th attacks and for much of the war on terror, the CIA widely used waterboarding as a form of “enhanced interrogation” to get information from suspected terrorists. Waterboarding is widely considered a form of torture and raised a lot of ethical and moral concerns about how we were conducting ourselves in this war on terror. Questions that were raised: Is waterboarding torture? If so, is torture ever justified?
For a basic description of the technique take a look at the wikipedia page.
In 2008, Vanity Fair writer, Christopher Hitchens, volunteered to be waterboarded because he did not believe the technique constituted torture. Below that is the article he wrote about his experience and below is a video of his experience that changed his mind on the technique.