The standard foot soldier is the lowest ranking unit of the bunch. They are usually the first line of defense and are equipped with medium grade armor. Usually they carry around the AK-74u or the Mossberg 590

 Whenever there is a need for containing hazardous materials, the scientist is key to figuring out constructive solutions. Although they have virtually no ballistic armor, which makes them easy targets, they usually are well equipped with the notorious PPSh-41

 The squad leader is usually the head of the squad. They give out strategic orders and feed intel back to headquarters. They usually sport the AK-74u or SKS as well as a few hand grenades.
 

 This unit specializes in areas with heavy radiation and nuclear waste. They are sent in to protect the Scientists while they continue to research the affected areas. You will see them equipped with the deadly AMX-50K 

 These combat veterans are well equipped, highly trained and are heavily armored. This is the only unit that wont die easily from head shots, so bring out the big guns! They carry the infamous AKM along with night vision, among other high-tech gear.

 The expert marksman usually engages enemy targets from concealed positions or at distances. Snipers are equipped with high-precision rifles (like the SVT-40) and often relay information back to their squad leader. They usually maintain their position at higher ground.