While taking a class on war and the Clausewitzian principles found there in, I had a chance to learn about where the term "stormtroopers" actually came from. Hitler was not the first to use the term in Germany. It comes from the German Sturmabteilung or "Storm Division." Sometimes they were called Sturmtruppen. They were initially used in WWI in trench warfare.
There was a German officer but the name of Oskar von Hutier who realized that the way the Allies and the Germans fought trench warfare was extremely ridiculous. First, a heavy artillery barrage would start and then after that swarms of infantry would try to overtake the enemies trenches. If anyone has studied the battles of WWI, one would note the tremendous casualties taken just to defend or invade a few hundred yards of trenches.
Hutier decided to recruit the most elite members of the infantry and form them into small units. During the heavy artillery barrages, he would send these shock troops or "storm troops" right behind the barrages. To the Allies, these troops appeared out of the "storm." Their job was to hurl explosives at communication depots, officer encampments, and artillery posts to weaken enemy positions. It was a dangerous job but proved to be successful. Later Hitler used to moniker to create a group of para military thugs that would later become the SA.
Connection to Star Wars...
Many Star Wars theorists claim that George Lucas made the empire seem like Hitler's Third Reich hence all the Imperial officers with the Nazi like appearances. This of course has never been proven. Others argue that the Stormtroopers in SW were supposed to be elite. If one reads the Expanded Universe, one will learn that they were elite and were very feared. The Empire does have its regular infantry.
However, throughout the movies we see them as bumbling idiots or keystone cops. Yet they are still feared throughout the galaxy.