Before the start of WWII, there were several types of guns each with their individual strengths and weaknesses. Some could fire in rapid bursts, some could hit incredibly hard, some were light enough to be handheld. A weapons designer named Hugo Schmeisser took it upon himself to create a weapon that had the best of those properties into a single weapon for Germany infantry units, the StG 44.
At first, Hitler opposed such a weapon, thinking that basic rifles would be enough for the troops to conquer the battlefield. However, after a demonstration of the effective power of this gun, he changed his mind and gave it the name Sturmgewehr which roughly translates to assault rifle.
Like many powerful German weapons, the StG came too little too late to have an effect on the outcome of the war. But the Sturmgewehr did have a strong influence on a Russian inventor named Mikhail Kalashnikov who improved upon its design to bring forth a weapon that endures to this day, the AK-47.
“Thank goodness hundreds of thousand weren’t pumped out earlier in the war. That would have cost a whole lot more American lives even if it wouldn’t have affected the outcome. And thank god the Japanese never came up with anything like that.”
– Captain Dale Dye, USMC (Military History Consultant and President of Warriors Inc.)
It was a very brutal weapon that led to the evolution of guns as a whole. Weapons experts go into further detail on the history of the StG 44 in this clip from Weaponology.