After weeks of planning and preparation, General Zhukov's offensive begins. The intention is to extend a pincer movement with armies from the Southwest Front (Army Group) lead by Vatutin and the Don Front, lead by Rokossovsky, attacking southward from the Don concentrating between Kletskaya and Kotovskiy. The Stalingrad Front (Army Group) under the command of Yeremenko, is to attack westward from the south of the city. The Soviets have assembled more than half a million men, 900 new T34 tanks, and masses of artillery and over 1,000 planes.

The northern arm of the pincer strikes first. The 5th Tank Army, 21st Army and part of the 1st Guards Army breakthrough near Kletskaya held by seven divisions of the Romanian 3rd Army. The attack is intense and rapid and the Romanians have no chances of withstanding the onslaught. Meanwhile in the Caucasus, the Soviet win an important battle near Ozdzhonikidze. Bad weather in the area ends most major operations, but Soviet small gains continue.

The Romanian troops conducted an almost miraculous defense and managed to hold the line for one day. The situation was hopeless however, they were outnumbered some 3 to 1 (almost 7 to 1 in tanks), and had little modern equipment to face the fresh units being sent in against them. On the 20th their line had been breached and huge numbers of Red Army divisions started streaming south.

Also on the 20th a second attack was launched to the south of the city against points held by the Romanian 4th Army, made up primarily of cavalry, and this army collapsed almost immediately.

The Soviet attackers met in a pincer movement near Kalach two days later, trapping 300,000 Wehrmacht soldiers of the 6th Army and about half of the 4th Panzer Army in and around Stalingrad, and shattering both Romanian armies in the process.

Hermann Göring promised that all the necessary supplies for the 6th Army could be delivered by the Luftwaffe. This would allow them to fight on while a ground force was assembled to re-open the line.

If this worked, the tables could be turned, with the Red Army units on the "far side" of the Don suddenly surrounded by troops in the city and newly arriving units from the west.

This strategy had been used to great effect the year before, but on a much smaller scale and during the summer.

Supplying the 6th Army would require 300 T to be delivered each day, and by any count the number of planes needed to achieve this was clearly not available. However the claim, once stated, could not be withdrawn, and Adolf Hitler backed Göring's plan and re-iterated his order of "no surrender" to his trapped armies.

The supply mission failed almost immediately. The winter weather offered few occasions when the planes could be flown in, with one or both ends of the flight-path covered in clouds and snow. On days with good weather about 280 T would arrive, but there were only two of these over the next two months. In general only 1/10th of the needed supplies were able to be delivered.