Let's talk about torture. An expert interrogator can get information out of almost anyone. But not everyone, and for these stalwarts, there remains one option. But there are many people who resist torture unto death. While some people respond more to torture than to psychological pressure, the widespread use of torture is generally an indication of a lack of experienced interrogators. At Guantanamo Bay, and other locations where large numbers of terrorist suspects were interrogated, if was found that, kindness was more likely to open them up. A cheeseburger or heath care (like a hearing aid or eyeglasses) made the subjects so appreciative that they eagerly answered all questions put to them. Even those who had been warned by their leaders to say nothing, responded to kindness. Medical care was particularly appreciated, especially as many of these men had never received much of it.
At the start of the war on terror, America didn't have enough experienced, Arab-speaking interrogators to get much out of these suspects. So, using translators, interrogators had to improvise as they went along. All knew about the old "good cop/bad cop" routine, and that's where the positive effect of fast food and eyeglasses was discovered. Some of the hard-core terrorist suspects only responded to torture. It was initially believed that some of the true believers would resist physical pressure well. This never happened. And forget about lying to stop the torture. Interrogators have known, for thousands of years, how to insure that the extracted information is true (by having some questions you already have true answers for, or quickly checking out each answer.)
For thousands of years, torture has been a common practice. But a lot of that torture was done not just to obtain information, but more often to terrorize a population or, as fans of violent sports are reluctant to admit, to provide entertainment. Then the 20th century brought the scientific method to bear on the use of torture. When the objective was mainly to obtain information, be it military secrets or a confession from someone innocent of a crime, many new forms of torture were developed, perfected and widely used.
But one constant was the need for an expert interrogator. This has long been recognized. The infamous medieval Inquisition used a lot more quiet questioning than it did gruesome forms of physical torture. The 20th century torturers also perfected the art of psychological torture. The best criminal investigators have a large bag of interrogation techniques, which often obtain the desired information without any physical contact with the suspect.
The Soviet Union, over its seven decades of existence, literally wrote the book on non-physical torture. Part of this was due to the nature of the communist nations. They were police states and were constantly on the lookout for disloyalty. But the Soviet Union had another major advantage; it was able to create thousands of expert, career interrogators. These were men, and a few women, who spent decades perfecting their skills. The Soviet Union had several college level institutions that amassed and passed on vast amounts of knowledge and technique in the use of physical and psychological torture. Some of these schools are still operating.
Despite the considerable skills of the communist interrogators, they were not always able to get the information, or confessions, they wanted. But that's only because they practiced torture on so many thousands of people. There are always some who will remain silent unto death. Not too many, so the torturers continued confident that they would get what they wanted most of the time.
World War II saw an enormous amount of torture. The Nazis, who openly admired the superior interrogation skills of the Soviets, were more prone to use poorly trained investigators who went to physical torture quickly. The results were often dismal. Thousands of Russian and Allied victims took their secrets to their (usually unmarked) graves. The Soviets proved that, if you have the time (weeks or months) and skilled interrogators, you can break just about anyone. As for the few who resisted everything, a bullet in the back of the head was the usual result. The Soviet interrogators were not good losers.
One of the Soviet techniques that got more attention than success was the use of drugs to loosen tongues. The classic "truth serum" is sodium pentothal, which is basically an anesthetic. Much earlier, booze or drugs were used, with some success, to get people to loosen up and talk. Female spies have long used erotic behavior and sex to get men to spill secrets. Using anesthetics has the advantage of being administered in more controlled doses, and less likely to be fatal. The Soviets learned that if you disorient a subject long enough, they lose touch with reality, and the need to keep silent.
During the first few decades of the Cold War, there was something of a "drug race" between the United States and the Soviet Union to develop more effective drugs for use as interrogation tools. LSD, heroin and many exotic chemicals were used in the search for the perfect truth serum. There were no breakthroughs, but many people in the interrogation business still keep an eye on new developments in anesthesia.
And there are new things worth watching. Many new anesthetics don't knock you out as much as they put you in an altered state where you don't notice, or simply don't remember, the pain. Doctors often warn patients that they may want to use another form of anesthetic, because these new ones (using combinations of tranquilizers and sedatives in an IV drip) have a tendency to cause people to say things they'd rather keep secret. No one has admitted to using these new anesthetics for interrogation, probably considering success in this area as a valuable military secret. Or perhaps there is simply worry that such use will simply be outlawed for interrogation.
But when you have to get critical information in a hurry, like where a terrorist group has hidden a bomb (perhaps a small nuclear one) or biological weapon, most people will not quibble about the use of torture. In this case it is literally a matter of life or death. For this reason, most intelligence agencies stay current on torture techniques. Just in case. Even when laws are passed forbidding the practice, intelligence agencies just file away the data on torture techniques, certain that during some future crises, the order will be given to obtain desperately needed information using any means necessary.