The Sturmgewehr 44 (StG44) was the world's first truly effective assault rifle. It was introduced by the German army late in WWII, and if the war had continued another year, the SG44 would have replaced every other rifle, light machine gun, and submachine gun in the Wehrmacht, including the antique Karabiner 98k and MP38. After the war the legacy of the StG44 resulted in the outright replacement of almost every infantry gun in the western world, serving as the direct inspiration for the Russian AK47, the most prolific gun in the world, and the indirect inspiration for practically everything else.
there is a media clip of one in use in the multimedia section