Sturmgeschutz

Cossacks with a StuG. Any ideas about what appears to be a letter "C" on the back of it?

Apparently, the letter denotes the AFV belongs to a Panzer Group e.g. a "K" would denote Panzer Group Kleist, I have been unable to identify a Panzer Group "C"
https://mistertretiakpresents.wordp...rman-camouflage-and-tactical-markings-part-2/

This image however is of Romanian soldiers posing by a StuG on the road to Stalingrad. Their operations in Russia were later crushed by Soviet Operation Uranus, destroying their forces on the Don river and trapping them inside Stalingrad. These men likely died in the city.
http://knowledgeglue.com/100-amazing-and-graphic-images-from-the-eastern-front-ww2-page-4/