of surrender but Paulus did not respond, and resistance continued for the better part of the month. On 10 January, the Don Front launched "Operation Ring" to reduce the Stalingrad pocket beginning with a 55-minute barrage from 7000 rocket launchers, artillery and mortars. The defenders fought tenaciously, even as their lines slowly collapsed, causing the Don Front 26,000 casualties, and destroying half its tanks in the first three days of the operation. On 15 January Rokossovsky was promoted to the rank of colonel general. On 16 January the main airfield used to supply the beleaguered 6th Army fell, and then after a pause of a few days, the offensive was renewed capturing the last operational airfield and finally driving the German back into the city proper on 22 January. On that same day General Paulus asked Hitler for permission to surrender but was refused. On 26 January the Soviets had broken the surrounded Germans into two pockets, and on 31 January, the southern pocket collapsed and Paulus surrendered. Within four days the last significant group of defenders surrendered to Rokossovky's command, finally ending the battle that marked the high-water mark of the German advance during the Soviet–German war. 1943: Kursk After the victory at Stalingrad the Russian forces advanced to a position that created a bulge 150 km deep and 250 km wide into the German line, around the city of Kursk. This subsequently became known as the Kursk Salient. Rokossovsky's command was moved to the north of the salient and was re-designated as a new front, which was twinned with the Voronezh Front, holding the south approaches. In February 1943 Rokossovsky wrote in his diary: "I'm appointed commander of the Central Front. It means that Stalin has entrusted me to play the key part in the summer Kursk campaign." Both the Red Army and the Wehrmacht prepared to make a decisive offensive in the summer of 1943 at Kursk. The Germans planned to drive two thrusts, one through each flank of the salient, and unite them at Kursk in order to cut off substantial Soviet forces, recover from the strategic loss at Stalingrad, and curtail further Russian advance. The Russians, alert to the coming attack, put their offensive plans aside and prepared for defense in depth with mass antitank units in prepared positions. In late June one German bomb load in a night raid hit Rokossovsky's HQ, and he