The limitations consist simply of applying the right medium at the right time. Radio broadcasts need be made only when receiving sets are known to exist. Written material should be dropped only to areas in which at least some people can read. (The OWI in China, at the request cf CBI Forward Echelon Headquarters, made up the leaflet showing pictures only. This was designed for the aboriginal hillmen between China and Tibet--to tell them to rescue downed American pilots. Broadcasting to these people would have been as profitable as spitting in the ocean. None of them could read, much less understand radio.) The probable number of listeners or readers should be calculated conservatively, taking enemy policing, amount of enemy interest, customs of the people, tension among enemy troops or civilians and other appropriate factors into account. Occasionally propaganda media exceed the expected limitations. The Americans and British dropped leaflets on Berlin. The leaflets had little key numbers in the corners, showing to which series they belonged, and could thus be arranged in series. The Germans prohibited civilians from picking up the leaflets. The Nazi authorities followed up the prohibition by sending the _Hitlerjugend_ and _Hitlermädel_ out to pick up the leaflets and turn them in for destruction. The boys and girls did their job with gusto. Vast quantities were turned in for destruction. What the Nazis discovered--too late, too late--was that the schoolchildren had begun collecting the leaflets, using the key numbers to make up perfect sets. Some numbers were rarer than others, so that the Hitlerite children swapped Allied leaflets all over Berlin, trying to make up attractive albums. Mother and Father--who did not dare pick the leaflets up off the street for fear the Gestapo might be watching--found a convenient file, reasonably complete, in the room of little Fritzl or Ermintrude! The most hopeful British or American planner could not have counted on such a happy result. =Maximum Performance of Personnel.= Another limitation, to be found in any psychological warfare operation, is that imposed by the types of personnel available. It would be a rash commander who assumed that he had air support because he saw airplanes--without knowing whether air crews were available. A microphone does not make a propagandist. Personnel using the speaking voice have to be good speakers; merely knowing the language is not enough. Writing personnel must be up to the level of professional writers. On the other hand, the available personnel must not be driven above its limits of performance: often an attempt to do a too-professional job will defeat the propaganda. (When the Japanese pretended to be perfectly American, and used the corny obsolete slang of the 1920's, they aroused more contempt than they would have done had they confined themselves to rather bookish, plain English.)