By 10 August, the Red Army had been cleared from most of the west bank of the Don, but Soviet resistance continued in some areas, further delaying Army Group B. The "Wehrmacht" advance on Stalingrad was also impeded by supply shortages caused by the poor state of Soviet roads. The "Luftwaffe" sent an ad-hoc force of 300 Ju 52 transport aircraft, enabling the Germans to advance; some bombers were diverted from operations to supply flights under the "Stalingrad Transport Region force". The Soviet defence at the Don forced the Germans to commit more and more troops to an increasingly vulnerable front, leaving few reserves to back up the Axis divisions on either flank. The Soviets made several counter-attacks on the northern flank of Army Group B, between Stalingrad and Voronezh. From 20–28 August, the 63rd Army and the 21st Army counter-attacked near Serafimovich, forcing the Italian Eighth Army to fall back. The 1st Guards Army attacked near Novo-Grigoryevskaja, extending its bridgehead. These and several other bridgeheads across the Don, opposed by the Eighth Italian and Second Hungarian armies, were a constant danger.