At the start of the war, the Springfield bolt action 1903 Model A3 was the standard issue rifle. It was an improved version of the one used in WWI. It was produced until early in 1944 even though the newer Semi-Automatic M-1 Garand was by that time the first line issue infantry weapon. In addition, the WWI vintage Browning Automatic Rifle (BAR) was issued as the squad automatic weapon. The Army issued one per 12 man squad. The Marines issued two.
The M-1 Carbine Semi-Automatic was issued to officers and other weapons crews as a personal sidearm a step above the 1911 Model Colt Semi-Automatic pistol. This carbine was made fully automatic later in the war and was redesignated the M-2. It was our first fully automatic assault weapon and was used by the airborne. It fired a .30 cal cartidge but was underpowered, falling in the class of a pistol cartridge. The M-1 and M-2 Thompsons were favored as a squad submachine gun but due to manufacture techniques there were never enough to go around to meet demand. The M-1 and M-2 Greasegun submachine gun was designed to fill theis gap and was issued to tank crews and infantry squads. The quality of this weapon was poor, but was cheap and easy to make. The 1903 Springfield (also manufactured by Remington and Smith Corona, yeah the typewriter people) saw service as a sniper rifle from WWII to Viet Nam. Until recently you could by one through the NRA Civilian Marksmanship program for $125 to $400 dollars with range qualification. They have all been sold and now go for as much as $1200.
You might notice the problems having weapons firing 3 different cartridges might have caused for logistics. The 1906 .30 caliber or .30-06 rifle cartridge for the M-1 Garand and 1919 Light Machine gun, the .30 carbine cartridge for the Carbine, and the .45 cal ACP for the 1911 Colt, Thompson and Grease gun.
Squads were also equiped with the 1919 .30 cal Browning Light machinegun. These were squad support weapons usually found in the Weapons Platoon. Theis platoon also included the M-2 Browning .50 caliber heavy machine gun. This was not frequently found in the line squad, but was used by the weapons platoon. The 1919 .30 cal medium machine gun was a water cooled version of the 1919 light machinegun with a water jacket and heavy tripod.
It is interesting to note that the Wehrmacht had an MG-34 or MG-42 as the squad weapon and the squad members simply provided security support and ammo for the gun. Our forces employed the automatic weapon in the opposite fashion. But now, our troops are employing tactics more in line with the WWII german tactics. We now have two M249s (the Minimi)per squad and they are the center for the two fire teams that make up the squad. The Marines have three I think, with 3, 3 man fire teams. High volume fire power is a wonderful thing…