Supported by 2,035 Luftwaffe aircraft and 1,934 tanks and assault guns, the 1,370,287-man Army Group South attacked on 28 June, advancing 48 kilometers on the first day and easily brushing aside the 1,715,000 Red Army troops opposite, who falsely expected a German offensive on Moscow even after "Blau" commenced. The Soviet collapse in the south allowed the Germans to capture the western part of Voronezh on 6 July and reach and cross the Don river near Stalingrad on 26 July. Army Group B's approach toward Stalingrad slowed in late July and early August owing to constant counterattacks by newly deployed Red Army reserves and overstretched German supply lines. The Germans defeated the Soviets in the Battle of Kalach and the combat shifted to the city itself in late August. Nonstop Luftwaffe airstrikes, artillery fire and street-to-street combat completely destroyed the city and inflicted heavy casualties on the opposing forces. After three months of battle, the Germans controlled 90% of Stalingrad on 19 November.