As there was a necessity to find out quickly if the prisoner was a "Linecrosser" just in case sabotage was part of the mission (see Israli "ticking bomb" principle) they would often use "field expedient" interrogation methods.
The whole idea was to get the information and leave the prisoner alive and unscarred for trial should one prove to be politically expedient.
The prisoner was placed on his knees with hands bound to ankles. The head was pulled back and soapy water was poured in the nose and mouth.
Simple and cheap procedure leaves no marks. Repeat as required until desired result is obtained.
There are also several interesting uses for hand cranked field telephones (90volt ringing current no burns.)