Gentlemen,
...Why did so many type's of assault weapons like the M1 Carbine, MP 44 Sten Guns Tommy Guns etc., Start to be built and used so early during WW 2.
Thanks again
Clancy
ps could use some help TIA
www.garandm1rifle.com

If you are referring to the need for fully-automatic hand-carried weapons, here is what I have learned. Shortly after the onset of WWII, there was a need to have a hand-carried weapon that could provide the same type of suppressing fire that a machinegun offered. The M1 Carbine was a alternative to the M1 Garand. Many SNCOs and officers carried the M1 Carbine instead of the M1 Garand. The .30 Carbine round was considered am intermediate round. It was effective in reaching targets out  to 150-200 yards. This was further than the 45ACP that was used in their 1911s. The Thompson M1 submachinegun was used sheerly for hard-hitting 45ACP suppressing fire. It was much lighter to carry than the BAR, not to mention the difference in the weight of the ammo that had to be carried. The STEN was created out of necessity. When the Brits started having problems getting more of the Thompsons (because the shipments were getting sunk), the need arose for something else and quickly. That is when they came up with the idea of making a  9mm submachinegun. Basically, using a couple of pieces of pipe, a couple springs, and a few other small pieces, thay came up with a fantastic, compact, highly effective weapon. Later on in WWII, the STEN was also made in Australia. Germany's contribution was the MP40 and the Sturmgewehr 44. The MP40 was their 9mm submachinegun and the STG-44 was their "Assault Rifle". This was a weapon that utilized the 7.92x33 Kurtz round (basically a shortened Mauser round) fed via a removable magazine, and was capable of selective fire. The STG-44 was to combat our M1 Garand. Unfortuantely for Germany, the weapon was short-lived. The MP40, however, was a fine weapon that was used by not only the Germans, but by the Brits and some U.S. troops as well. I hope this answered your question. Someone else may have additional info.

I think militaries started to realize that the volume of fire, especially at shorter ranges, was more important than long range accurate fire.  Inklings of what ALCLAD and its progeny would later confirm.