As basic infantry, riflemen often take the brunt of an assault. They are armed with assault rifles that just entered widespread use at the beginning of the war (AK-47 in the Soviet Union and the M16 among the Allies) and usually don't wear much protection - usually only fatigues and steel helmets.
As the weakest, cheapest unit, they are useful as scouts (due to their good speed) and as early warning sentries (since they can be posted in remote locations).
Red Alert Universe
Although the game manual says the Allied soldiers are armed with M16s and Soviet soldiers with AK47s, the game code identifies both weapons as M1 carbine, which would also be more realistic for the time period