Hitler’s Directive No. 45 of July 23, 1942, revised the original plan of the German summer offensive in southern Russia. According to the directive, the offensives in Stalingrad and the Caucasus were equally important and would be pursued simultaneously. Army Group A [Heeresgruppe A] was to occupy the oil fields of the Caucasus, while Army Group B [Heeresgruppe B] was to conquer Stalingrad, an important industrial city and rail hub on the Volga River. In 1940, Stalingrad (named Zarizyn until 1925, and Volgograd since 1961) had a population of 450,000. The battle for Stalingrad began on August 19, 1942; on August 23, the 6th Army, under the leadership of General Friedrich Paulus, was ordered to take the city. Bitter fighting ensued and losses were extraordinarily high. The battle for Stalingrad lasted until February 2, 1943, ending in a crushing German defeat.