The winter of 1941-1942 basically immobilized both the German and Red armies. Cold, snow and mud made movement at scale virtually impossible. The German high command – at this point Hitler – planned Case Blue, an offensive to begin in July 1942 to attack and take the Caucuses oil fields and to also take Stalingrad. The German 6th Army reached Stalingrad on September 1st and the battle became one of street to street and house to house. The city was virtually destroyed by the fighting and the German Army controlled 90 percent. It became a battle of attrition. In November 1942 the Red Army unleashed a massive counter attack and virtually trapped the 6th Army in Stalingrad and cut off the supply lines. On January 1, 1943 the Soviet Commander asked for the surrender of the German forces but Hitler told the German Commander, Field Marshal Paulus, to stand to the last man. Paulus was captured on January 31st and the last German forces surrendered on February 2nd. On the 350,000 German troops that entered the city, only 90,000 were left to surrender.