I'm looking for websites, books, etc. that detail specific techniques used to withstand torture. Everything I've found on Google is geared towards recovery from past torture/ritual abuse, rather than techniques used while torture is taking place to stay sane. I know that military personnel are taught this kind of thing, but I can't seem to find a resource that gives details on what they are taught.
I've got a character who is an experienced spy, and he is waterboarded and interrogated/emotionally abused early on in my story. I want to establish how horrific the torture is, but I also want him to come across as someone who's been tortured before and knows how to deal with it.
Any help would be appreciated!