This map depicts the dramatic change of events as the Soviet Army implemented "Operation Uranus" against the German invaders at Stalingrad. By January of 1943, Soviet forces were surrounding what was left of the German Army.
Hitler, meanwhile, was dumbfounded that such a reversal of fortune could ever occur. He promoted General Paulus to Field Marshal, expecting that he would thereafter take his own life (since no German Field Marshal had ever surrendered).
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Map image, described above, online courtesy On War.