4th Panzer Army was the Soviet 6th Guards Army, which was composed of the 22nd Guards Rifle Corps and 23rd Guards Rifle Corps. The Soviets had constructed three fortified defensive belts to slow and weaken the attacking armoured forces. Though they had been provided superb intelligence, the Voronezh Front headquarters had still not been able to pinpoint the location where the Germans would place their offensive weight. Initial German advance XLVIII Panzer Corps The panzergrenadier division Großdeutschland (Walter Hörnlein), was the strongest division in the 4th Panzer Army. It was supported on its flanks by the 3rd and 11th Panzer Divisions. The Panzer IIIs and IVs of the Großdeutschland had been supplemented by a company of 15 Tigers, which were used to spearhead the attack. At dawn on 5 July, Großdeutschland, backed by heavy artillery support, advanced on a three-kilometre front upon the 67th Guards Rifle Division of the 22nd Guards Rifle Corps. The Panzerfüsilier Regiment, advancing on the left wing, stalled in a minefield and subsequently 36 Panthers were immobilized. The stranded regiment was subjected to a barrage of Soviet anti-tank and artillery fire, which inflicted numerous casualties. Engineers were moved up and cleared paths through the minefield but suffered casualties in the process. The combination of fierce resistance, minefields, thick mud and mechanical breakdowns took its toll. With paths cleared, the regiment resumed its advance towards Gertsovka. In the ensuing battle, many casualties were suffered including the regimental commander Colonel Kassnitz. Due to the fighting, and the marshy terrain south of the village, surrounding the Berezovyy stream, the regiment once more bogged down. The panzergrenadier regiment of Großdeutschland, advancing on the right wing, pushed through to the village of Butovo. The tanks were deployed in a Panzerkeil (arrow) formation to minimise the effects of the Soviet Pakfront defence, with the Tigers leading and the Panzer IIIs, IVs and assault guns fanning out to the flanks and rear. They were followed by infantry and combat engineers. Attempts by the VVS to impede the advance were repulsed by the Luftwaffe. The 3rd Panzer Division, advancing on the left flank of Großdeutschland, made good progress and by the end of the day had captured Gertsovka and reached Mikhailovka. The 167th Infantry Division, on the right flank of the 11th Panzer Division, also made sufficient progress, reaching Tirechnoe by the end of the day. By the end of 5 July, a wedge