The Russians won because of the T-34 Tank, without it, they would have lost the war.
A German General who came across the T-34 for the first time, remarked, that if the Russians could build them on an assembly line, Germany would lose the war.
The T-34 was an excellent tank. That was the Soviet’s strong suit, no doubt there.
There was also the little matter of a huge number of Studebaker trucks which were built on an America-created assembly line in Iran from parts manufactured in the US and shipped to Iran. They were initially shipped assembled, but that required far more scarce ship transport than the parts, which could be shipped so much more compactly.Each truck was loaded with materiel needed by the USSR, and the keys were turned over to Soviet Army drivers who would travel in convoys through Iran to their destinations. After unloading, the trucks provided the Red Army infantry with vitally needed mobility.