Germany's armored forces had sustained heavy casualties. It was unusual for a Panzer division to field more than 100 tanks, and most averaged only 70–80 serviceable tanks at any given time. After the fighting around Kharkov, Heinz Guderian embarked on a program to bring Germany's mechanized forces up to strength. Despite his efforts, a German panzer division could only count on an estimated 10,000–11,000 personnel, out of an authorized strength of 13,000–17,000. Only by June did a panzer division begin to field between 100 and 130 tanks each. SS divisions were normally better equipped, with an estimated 150 tanks, a battalion of self-propelled assault guns and enough half-tracks to motorize most of its infantry and reconnaissance soldiers – and these had an authorized strength of an estimated 19,000 personnel. At this time, the bulk of Germany's armor was still composed of Panzer IIIs and Panzer IVs, although the SS Division Das Reich had been outfitted with a number of Tiger I tanks. The 4th Panzer Army was commanded by General Hermann Hoth, while the First Panzer Army fell under the leadership of General Eberhard von Mackensen. The 6th, 11th and 17th Panzer Divisions were commanded by Generals Walther von Hünersdorff, Hermann Balck and Fridolin von Senger und Etterlin, respectively. The SS Panzer Corps was commanded by General Paul Hausser, who also had SS Division Totenkopf under his command. Red Army Since the beginning of the Red Army's exploitation of Germany's Army Group South's defenses in late January and early February, the fronts involved included the Bryansk, Voronezh and Southwestern Fronts. These were under the command of Generals M. A. Reiter, Filipp Golikov and Nikolai Vatutin, respectively. On 25 February, Marshal Rokossovsky's Central Front also joined the battle. These were positioned in such a way that Reiter's Briansk Front was on the northern flank of Army Group South, while Voronezh was directly opposite of Kursk, and the Southwestern Front was located opposite their opponents. Central Front was deployed between the Briansk and Voronezh Fronts, to exploit the success of both of these Soviet units, which had created a gap in the defenses of the German Second Panzer Army. This involved an estimated 500,000 soldiers, while around 346,000 personnel were involved in the defense of Kharkov after the beginning of the German counterstroke. Like their German counterparts, Soviet divisions were also seriously understrength. For example, divisions in the 40th Army averaged 3,500–4,000