With the Senate Torture report in the news, one of the arguments against torture is that it is ineffective: torturing someone just makes them tell you anything they think will make the torture stop, leading to a lot of unreliable information that must now be investigated to find any, if, useful information. 

**Do we know of any historical assessments of the effectiveness of torture?** What were the Gestapo's views on torture, or those of the KGB? I read about [Hanns Scharff](http://en.wikipedia.org/wiki/Hanns_Scharff) the other day, a successful German interrogator during WW2 who expressly opposed the use of physical torture, but then on the other hand torture has been and is widely used.

It's maybe also worth to specify that this is about the effectiveness of torture for **extracting reliable information** one couldn't get without it, not whether torture is effective for punishing people or deterring others.