The Allied airmen who were shot down over Germany and passed through the interrogation center at Oberursel had all been trained to give name, rank and serial number and nothing else. A great many of them nonetheless told Hanns Scharff a good deal more than that, and most of them did not realize they had.
Scharff was not a professional intelligence officer. He was a businessman who had lived in South Africa, spoke fluent English, and ended up in the job by accident. He interrogated hundreds of captured Allied fliers, including several senior aces, and his results were exceptional. He never used physical coercion, and he regarded shouting as a confession of failure.
His method had a small number of components.
He read everything first. Before meeting a prisoner he assembled a dossier from crashed aircraft, previous interrogations, intercepted mail, American newspapers and unit histories, so that he arrived knowing squadron names, commanding officers, base gossip, and details of the prisoner's own life.
He then presented himself as already informed. The conversation was not a series of questions but a friendly, well-briefed monologue with gaps in it. He would recount what he knew about the prisoner's squadron, sometimes with a deliberate small error, and the prisoner — who believed the information was already in German hands and that correcting a trivial detail cost nothing — would supply the correction.
He was genuinely kind. Walks in the woods. Real coffee. On at least one documented occasion, a flight in a German aircraft. He treated the prisoner as a fellow professional, and the affection several of the men later expressed for him was not an act on their part.
Granhag and colleagues have since operationalized this and tested it experimentally, comparing what they call the Scharff technique against direct questioning. Their consistent finding is twofold: the Scharff approach yields more new information, and — the important part — sources subjected to it substantially underestimate how much they revealed, while sources questioned directly overestimate it.
That second finding is the technique's real product. Direct questioning tells the source exactly what the interrogator wants, which allows a deliberate decision about what to withhold. The illusion of knowing it all removes the decision entirely, because there appears to be nothing to protect.
Cialdini's principles are visible throughout — reciprocity from the hospitality, liking from the genuine warmth, and the confirmation-seeking dynamic that makes correcting an error feel like an insignificant act rather than a disclosure.
The defensive lesson is uncomfortable, because the natural counter — refuse to talk to anyone friendly — is neither practical nor what the mechanism turns on. What matters is the assumption that information already known cannot be given away. It can. Confirmation is intelligence: knowing something and having it confirmed by a person in a position to know are different states, and the second is what elicitation is buying.
Cross-ref: SUE and elicitation chapters