Panzerkampfwagen III of Army Group South advances through the Kuban Steppe to the Caucasus Mountains during Operation Blue. Intending to secure the oil fields in Baku in the Azerbaijan Soviet Socialist Republic, Reichchancellor Adolf Hitler ordered Army Group South to complete the operation quickly and was frequently frustrated with their progress. Only ten percent of the Red Army was in the south; the limited number of prisoners convinced Hitler that the Soviets were running out of manpower. 1st Panzer Army under Generalfeldmarschall Paul Ludwig Ewald von Kleist (August 8, 1881 - November 13, 1954) attacked Rostov, which fell on July 28, 1942. Learning from their mistakes, the Red Army withdrew without losing large formations in encirclements. On August 9, 1st Panzer Army reached the foothills of the Caucausian mountains, having advanced more than 300 miles. The 6th Army was stalled in taking the city of Stalingrad, rendering these gains negligible for the Germans. On August 21 a Nazi flag was installed on Mount Elbrus, the highest point of Caucasus. Hitler comments that his Army's ambition should be to defeat the Russians rather than conquer mountains. By September the Sixth Army is engaged in protracted urban street fighting in Stalingrad.