What is an “Assault Rifle” and where did they come from? Reasonable questions and not too complicated to answer. To identify what an assault rifle is today we really should look into the past to see how they evolved.
Back in the First World War, our troops as well as those of the other forces, were armed with bolt action rifles. These were powerful rifles and each round had to be manually chambered by operating the bolt. These weapons were not well suited to the trench-style warfare of WW I.
During World War Two, the Germans used the same 98 Mauser while we adopted the M1 Garand. The M1 was very successful as a standard military rifle but when it came to close combat in cities and towns it was not ideal. What was really required was a rifle that was smaller, easier to operate in confined situations, and had a rapid fire capability.
The Germans developed one of the first “Assault Rifle” during WW II. It was a compact automatic rifle, utilizing a high capacity magazine and a small rifle type cartridge, but was not produced in sufficient quantities to make an impact on the war. The Russians also were developing a smaller, lightweight, rifle called the SKS. The SKS utilizes the 7.62X39 medium size cartridge as does the follow on AK-47. The AK-47 replaced the SKS in the early 1950s and became the ultimate assault rifle in Russia as well as many other nations throughout the world. You can select either semi-automatic or automatic fire. The AK-47 is still considered the finest service rifle of all time by many.
Here in the US, we stumbled around for a number of years trying to find the proper replacement for the M1 Garand and finally settled on the M-16. The M-16 is the military version of the AR-15 and both utilize the 5.56X45 cartridge. While the civilian AR-15 is a semi-automatic, the military version has used automatic, selective fire (either full or semi), or the 3 round auto, where the rifle fires 3 rounds for each pull of the trigger. The biggest problem with the M-16 is that it fires the 5.56X45 cartridge, which in civilian life is the Remington .223, a cartridge designed for varmint rifles. No matter what you want to call it, it is still just a 22 and does not compete with the more powerful 7.62×39. Still, the M-16 is considered as an adequate service rifle. It is lightweight, has reasonable range, lite recoil, large capacity magazine, and allows a soldier to carry more ammunition due to the small cartridge.
The AR-15, the civilian semi-automatic version of the M-16, is not really adequate as a big game hunting rifle, after all, it is only a 22. However, the AR-15 is found on shooting ranges from coast to coast and in competition with both civilian and military marksman throughout the country. As the standard military rifle of the United States, this assault rifle is now an American standard with both the military and the civilian shooters.