In November, 1942, three months after the battle of Stalingrad began, the Soviet Union, launched Operation Uranus, a counterencirclement of the German forces in and around the city, in two prongs.
The larger, northern prong debouched from the south bend of the Don heading southeast, and four days later reached the appointed rendezvous point at Kalach, 40 miles west of Stalingrad, which contained the main German line of communications.
A day or so later, the smaller, southern prong of the attack was launched from the west bank of the Volga, on a northwesterly course with Kalach three days distant. About one day into the advance, it was counterattacked, and briefly halted by the German 29th Motorized Division, before this division was redeployed to resist the northern thrust. But had the Germans known what was going on, they might have reinforced the 29th Motorized, and at least stopped the southern thrust from arriving at Kalach to complete the encirclement.
Suppose this had happened. Was the capture of Kalach by the northern group sufficient by itself to isolate the Germans? Is there reason to believe that the northern thrust would have been able to complete the encirclement on its own by marching past Kalach to the Volga if this were not the case? Or would the Germans have been able to escape from Stalingrad if they had managed to stop the southern thrust from reaching Kalach?