What if, good uncle Joe decides that during the battle of France is the right moment to stab Grofaz in the back. Yes during the Winter War the Red Army didn't do so we'll, but at Khalkhin Gol last summer, Zhukov proved that in the right circumstances and with an adequate strategy it could do quite a show. Stalin knows that Germany must finish with the western allies first and a great deal of the Whermacht will be deployed in the west. So with a few hundred thousand or maybe a few million workers, don't know how many is plausible, working around the clock, can they improve the rail network in soviet ococcupied Poland, to supply, maybe 3 million men with 5000 tanks and 5000 airplanes, before the summer of 1940? So in may 1940, when the germans are heavily involved in France, with the armored spearheads racing towards the English channel, Stalin decides that he won't get another chance like that an gives the order to "liberate" Europe. How much can they advance and how will the germans (Adolf) react ? I suppose that the french won't surrender in those circumstances.