 Complete the following phrase:  Between 13 November and 31 December, the 1st provided air defense for the 21st Army in its concentration areas for Operation Uranus, the Soviet counteroffensive at Stalingrad, the crossing of the Don River, the breakthrough of enemy defenses in the Kletskaya area, the insertion of mobile groups into the breakthrough, the pursuit and encirclement of German troops, and the blockade of the surrounded German troops at Stalingrad. From 1 January to 2 February 1943 the division provided air defense for the army during 