Propaganda in the War.
Propoganda was used to arouse the citizen interest in the war, so it was most likely used before the US actually entered WWII, therefore it most likely went into wide usage in the 1940's through the end of the war.

During the second world war propaganda had two major players, the United States, and the Nazi party. Propaganda was used for a variety of reasons on both sides. IN the United States when war seemed inevitable the citizens still were against joining the war. In the early days of the war it was vital to gain citizen support. There was a massive propaganda spike in the US that was meant to encourage war support and excite the common people. It was also important as a call for aid in the factories and manufacturing. This called out the need of workers to supply the American forces with weapons, aircraft, and the like. The German forces had superior weaponry at this time, so gaining the upper hand number wise was crucial. There was also a huge anti-spy mission, information was vital and it could not be risked to be leaked. Many of the US propaganda posters adressed Hitler directly, using his name as that the personification of evil, rather than the war or Nazis in general. Propaganda of this magnnitude and tone was never before and never after been seen.

United States propaganda: This image shows the need for conservation and the demotion of Hitler as the personification of badness.
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external image shadow.jpg
This is an image representing that the "dark shadow" was closer than it apeared.
Pitures from:
http://library.thinkquest.org/C0111500/ww2/american/amerprop.htm