here's some concept art of some basic variants of American infantrymen from the army and marines.
from left to right
the guys with the most basic kit, usually found guarding, and facilitating, installations behind the lines, or places that are deemed unimportant. they're also found manning emplaced heavy weapons, like machinegun nests, and artillery, when ecountered in combat. they don't have much in the way of self defense on the field since ideally, they should be manning heavy weapons, or guarding places where more effective weapons are withing reach.
they're usually armed with simple Springfield rifles or on some rare occasions Remington 8 semi-automatic rifles, the only serious piece of firepower they have are Flare-Rifles used by their signalers as makeshift grenade launchers in combat.
these are the front line guys they're basically found in the everyday combat situations.
they're usually armed with Springfields and some Remington 8s as they're basic loadout, for assault and CQB some of them are armed with Winchester 97 Trenchguns and rarely Thompson SMGs. they also make use of frag grenades and smoke grenades.
usually found alongside the field troopers, these guys provide basic fire support with sustained small arms fire and some special weapons.
usually encountered with Browning Auto Rifles, more heavily armed units can also be seen with Hotchkiss machine guns, and for some special objectives, they can sometimes be seen utilizing flamethrowers.
basic marine infantryman, generally used as assault troops.
besides the standard issue Springfield rifles, Remington 8 SLRs are much more common, also given Thompsons as regular kit rather than solely for assault loadouts. Browning auto-rifles are preferred over the Hotchkiss for its lighter weight amongst their support teams. for equipment some Flare-Rifles are used, along with frag, smoke, and, incendiary grenades.
they're assault troops that specialize in close combat, like trench raiding, building storming, and room to room combat.
their general fare is the Winchester 97, but Browning Auto 5s are also common for when they need real quick-fire.
for equipment they sometimes use body armor and gasmasks especially. they make use of frag, flash, and gas grenades, and demolition charges, along with specialized ammunition for their shotguns.
basically marine scout snipers
though scoped Remington 8 SLRs are commonly issued many of their snipers still prefer the Springfield for its range accuracy and power.
for equipment they're issued camo smocks and netting, along with a series of sighting equipment such as, artillery spotter scopes, high power scopes and limited infrared optics. they also make use of frag, smoke, and flash grenades, along with specialized ammunition for their sniper rifles.
elite assault troops. you know shits about to go down when they're around
needless to say they pretty much have the entire arsenal of weapons and equipment in their hands, if it's needed to get the job done, they can call it in.
they're usually deployed rappelling down assault zeppelins which also act as close air support for a time being.