For the invasion of Russia, codenamed Barbarossa, the German army assembled some 3 million men, divided into 105 infantry divisions and 32 Panzer divisions. There were 3,332 tanks, over 7,000 artillery pieces, 60,000 motor vehicles and 625,000 horses. The Panzer divisions’ heavy armour at that time comprised some 439 Pz.Kpfw.IVs, but for light armour it had to rely on obsolete light tanks.
For the Russian offensive the Panzer divisions had been slightly modified in armoured firepower and diluted in strength in order to form more divisions. The planners thought that by concentrating a number of Panzer divisions together they would be able to achieve massive local superiority.
These new Panzer divisions contained one tank regiment of two, sometimes three, Abteilungen, totalling some 150–200 tanks; two motorized rifle (schützen) regiments, each of two battalions, whose infantry were carried in armoured halftracks or similar vehicles, and a reconnaissance battalion of three companies (one motorcycle, two armoured cars). The motorized infantry divisions accompanying the Panzer divisions in the Panzergruppe were similarly organized, but badly lacked armoured support. The divisional artillery comprised of two field, one medium and one antitank regiment and an anti-aircraft battalion. These were all motorised and more than capable of keeping up with the fast-moving Panzers.
When the German invasion of Russian was finally unleashed on the morning of 22 June 1941 the Panzer divisions progressed exceptionally well and continued over the next several weeks penetrating deeply into Russia. By late July the German armies were fighting on a front more than 1,000 miles wide. The Panzer divisions had exploited the terrain and struck such a series of blows to the Red Army that commanders predicted that it was only a matter of time before the campaign would be over.
Inevitably the Panzer divisions were thinly spread out, and they were moving so fast that supporting units were barely able to keep pace with them. Nevertheless, between June and late September 1941, the panzer and motorized divisions were more or less unhindered by lack of supply. Neither did the terrain or weather conditions cause them problems. However, on 6 October the first snowfall of the approaching winter was reported. It melted quickly but turned the dirt roads to mud. Autumn had arrived. The Panzer divisions began to slow. Wheeled vehicles became stuck and had to be towed. The attack had been launched later than intended and preparations for bad weather were inadequate. There were no chains available for towing vehicles, no anti-freeze for engine coolant systems, and soldiers had no winter clothing.
In blizzards and temperatures which fell 30 degrees below zero, the Panzer divisions soon ran out of fuel and, within sight of Moscow, ran out of ammunition and were compelled to break off their attack. On 6 December plans to capture the Russian capital in 1941 had to be abandoned.
By 22 December only 405 tanks were operational in front of Moscow, 780 were out of action but repairable, 2,735 had been lost, and 847 replacements had arrived since 22 June. Less than 1,400 operational tanks remained. The heavy panzers had borne the brunt, and now the front was vulnerable to enemy tanks such as the new Russian T-34.
By the end of 1941 the battle-weary divisions of the Panzerwaffe were no longer fit to fight. Mobile operations had ground to a halt. Fortunately for the exhausted crews and supporting units no mobile operations had been planned for the winter of 1941, let alone for 1942. In the freezing temperatures most were pulled out of their stagnant defensive positions and transferred to France, to rest, reorganize and retrain.
In spite of the terrible problems that faced the depleted Panzer divisions, back in Germany production of tanks increased. To overcome the mammoth task of defeating the Red Army, more divisions were being raised, and motorized divisions were being converted into Panzergrenadier divisions. Although equipping the Panzerwaffe was a slow and expensive process, it was undertaken effectively with the introduction of a number of fresh new divisions being deployed on the front lines.
It was recognised by German High Command that it was not just the volume of tanks that was required; they needed heavier, stronger tanks too, to counter the Soviet T-34 medium and the KV-1 heavy tank, which were superior to anything the Panzerwaffe had available on the battlefield. Tank designers were busy discussing plans for the production of a heavy tank to be known as the Panzerkampfwagen VI Tiger Ausf. E, later shortened to Tiger I.