I made some notes for a Vietnam gone WW3 setting where USA/ARVN are at war with China/PAVN. I think it'd be great because the mixture of weaponry present in Vietnam is almost as interesting as World War II. You had Carbines like the M1/M2 and SKS, Battle Rifles like the M1 Garand and M14 and MAS-49, Assault Rifles like the Type-56/AKM and M16, and Submachine Guns were not irrelevant yet. The use of helicopters would add some interesting abilities like dropping off a squad or acting as a temporary reinforcement point, not to mention close-air-support that is more responsive than loitering airplanes.
US ARMY
U.S.G.I. - US Army riflemen, their superior marksmanship allows them to excel at ranged combat, but they can be overwhelmed by close range attacks.
5 men with M14 Battle Rifles, can upgrade to 3 M16 Assault Rifles.
Ability to throw M26 Fragmentation Grenade, and fire M72 LAW.
Notes: USGI are designed to be contrasted with PAVN Troops, using long range semi-automatic weapons as opposed to the rapid-fire assault rifles. Their upgrade to M16 rifles improves their firepower at all ranges and reflects the Army's attempts to catch up to their adversary.
PEOPLE'S ARMY OF VIETNAM (NORTH VIETNAM)
PAVN Troops - Low quality Infantry with high quality gear, inferior at long range but can overwhelm an enemy with superior firepower up close.
6 men with Type-56 Assault Rifles, can upgrade to 1 RPD Light Machine Gun.
Ability to throw Fragmentation Grenade, and use undetermined anti-tank projectile.
Notes: Same as mentioned above, but the addition of a magazine fed light machine gun (automatic rifle style profile) will improve their damage and allow them to hold their ground once the Americans get M16's.
ARMY OF THE REPUBLIC OF VIETNAM (SOUTH VIETNAM)
ARVN Riflemen - The backbone of South Vietnam, the ARVN Riflemen suffer from outdated equipment, but make up for it in availability.
5 men armed with four M1 Garands and one M1918 Automatic Rifle, can be upgraded to 4 M2 Carbines OR replace M1918 with M1919A6.
Ability to throw Mk II Fragmentation Grenade, Fire M72 LAW.
Notes: The ARVN are equipped with US war surplus from past conflicts, they're heavily contrasted by the more modern PAVN. The free stock BAR helps lesson the blow of casualties against superior firepower, and they can be reconfigured for aggressive or defensive tactics with their upgrades.
PEOPLE'S LIBERATION ARMY OF CHINA
Skirmish Troops (T1) - Light infantry tasked with probing enemy positions and holding captured territory.
6 men armed with Type 56 Semi-Auto Rifles (SKS)
Abilities to be determined. May have some 'retreat from suppression' ability to emphasize their probing role.
Frontline Troops (T2) - Highly trained and devoted volunteers, these soldiers are best used to exploit gaps in enemy defences.
6 men armed with Type 56 Automatic Rifles.
Ability to throw Fragmentation Grenade.
Notes: The use of 2 stages of infantry is an interesting and unique concept, like Grenadiers and Panzergrenadiers or Conscripts and Shock Troops. The conceptual use is for Skirmish Troops to probe and engage the enemy while Frontline Troops take more aggressive actions. As the name suggests, Frontline Troops will become the predominant unit of the PLA by late-game.
Some other squads and units:
Check out Modern Combat for COH1 ;P
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cblanco ★ 
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VonManteuffel 
Heartless Jäger 
