While looks like a civilian vehicle, the GAZ truck was a general-purpose workhorse for the Russian forces during WWII, and was used as a frame for a wide variety of uses, including troop transport and a radio truck, along with the above anti-aircraft model.
The truck probably looks like a civilian vehicle, since the GAZ-AA was based on the Ford Model-AA, with the AAA being converted for heavier work with the third axel.
WWII, being the war of silly ideas like the bat bomb and human-powered torpedoes (along with some actually effective and scary inventions) saw these deployed in light battalions supporting ski infantry (an idea which the Russians stole from the Finnish after they were thoroughly beaten by said infantry).
Before the USA entered WWII, they regularly supplied the Allies with equipment, thus, the iconic Sherman is shown here in Russian colors.
An interesting bit I learned from researching this project was that it's common practice to use a variety of camouflage in one force, so the style and profiles are less easily identified. The Sherman, being a tall tank, felt appropriate in a striped camo pattern resembling a winter forest.