In April 1942, Stalin overrode Stavka by ordering the Soviets' first serious counter-attack, an attempt to seize German-held Kharkov in eastern Ukraine. This attack proved unsuccessful. That year, Hitler shifted his primary goal from an overall victory on the Eastern Front, to the goal of securing the oil fields in the southern Soviet Union crucial to a long-term German war effort. While Red Army generals saw evidence that Hitler would shift efforts south, Stalin considered this to be a flanking move in a renewed effort to take Moscow. In June 1942, the German Army began a major offensive in Southern Russia, threatening Stalingrad; Stalin ordered the Red Army to hold the city at all costs. This resulted in the protracted Battle of Stalingrad. In December 1942, he placed Konstantin Rokossovski in charge of holding the city. In February 1943, the German troops attacking Stalingrad surrendered. The Soviet victory there marked a major turning point in the war; in commemoration, Stalin declared himself Marshal of the Soviet Union.