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Most postwar publications on German armor of WW II tend to overemphasize the importance of the Tiger and Panther. These vehicles, while undoubtedly making quite an impression on their opponents during their somewhat limited appearance on the battlefield, should be considered as derivatives of the PzKpfw III and IV. These two tanks established the reputation of the German armored forces, and demonstrated the most advanced technical and tactical features of their time. Production of the PzKpfw IV was originally intended to be on a limited scale. Only the designer Krupp was engaged, while the PzKpfw III production was divided among eight major companies. 
The PzKpfw IV was originally given a limited role as a 75mm gun (75mm Kw.K. L/24) support vehicle for the PzKpfw III, which was equipped with a 37mm gun,  to complete the quartet of basic pre-war tank models, but it became the vital backbone of the Panzer force, more of this type being built than of any other. The sound principles used in the design of the chassis allowed it to be progressively up-gunned and up-armored so that it was expedient to continue production up to the end of the war, when some 8500 had been built. The turret ring was sensibly constructed with sufficient diameter to permit up-gunning without radical re-design. The PzKpfw IV used leaf springs, in contrast to the PzKpfw III, Panther and Tiger, who employed a torsion bar suspension. As the up-gunning and up-armoring process continued, the forward springs remained constantly bowed under heavy pressure, causing the vehicle to yaw badly. 
Ausf. C with 30mm 'Zusatzpanzer' on the hull front
Ausf. C with improvised box on the turret rear
One man most instrumental in the design of the PzKpfw IV was the creator of the German Panzertruppe, Colonel-General Heinz Guderian, who had laid down the basic prerequisites for armored fighting vehicles as early as 1933-34. These were mobility, fire-power, armor protection and communication. A five-man crew was also considered essential, as this allowed for a distinct allocation of duties between the crew, an advantage both in training and and in battle, which gave German tanks their marked tactical superiority over their Allied counterparts despite other shortcomings. For example, in contrast to the German three-man turret crews that worked as a team, the French preferred one-man turrets, which required the vehicle commander to act as his own loader and gunner with the result that he performed neither of these functions well under pressure. 
In spring 1935, Krupp, Rheinmetall, and MAN all sent in designs to fit the specifications drawn up by the Heereswaffenamt. This vehicle was known under the cover designation of Battalionsführer Wagen (BW), and the Krupp design was chosen for production. Prototype trails took place at Ulm and Kummersdorf in 1937. As with the PzKpfw III, some pre-production models were built in small numbers for trails. Three models, Ausf. A, B and C, had been built by 1939, and the few vehicles available took part in the Polish campaign, painted in the usual dark blue-grey of the German Army. There was little variety in detail, and also in the period 1939-1941 little was changed, for in service the PzKpfw IV was fulfilling its role. With the outbreak of the war the design was 'frozen' and large scale production was ordered as the Ausf. D. However the PzKpfw IV was destined to supplant the PzKpfw III as the mainstay of the panzer divisions, for its larger size allowed more efficient up-gunning and up-armoring. 
PzKpfw IV Ausf. D with the short-barreled gun
Replacing the engine
The only opposition encountered in Poland came from 37mm anti-tank guns, and losses were light. As a result of experience in Poland, armor protection had to be upgraded, but plans to increase the superstructure front to 50mm were delayed, which resulted in the acquirement of 30mm 'Zusatzplatten' (supplemental armor) for the PzKpfw IV Ausf. E. During the invasion of France in 1940, the superior deployment of German armor proved decisive, and neither the protection nor the fire power was greatly improved. The same story was repeated during the Balkan campaign of 1941 and the first appearance of the PzKpfw IV in North Africa. During this time, the PzKpfw III had replaced the obsolete PzKpfw I and PzKpfw II and fought, already up-gunned with a 50mm gun, most of the tank battles. 
Against the PzKpfw III, the PzKpfw IV's production was modest, as in 1941 only 480 vehicles were produced, despite an order for 2160 vehicles to equip the planned 36 armored divisions. Originally the main assembly was at Krupp, with hulls and turrets supplied by krupp and Eisen, but due to Allied air raids new key war industries were relocated to areas not readily accessible to the bombers. One of the new tank factories taking on the PzKpfw IV production was Nibelungenwerken in Austria, were the production and assembly remained till the end of the war
 A bridge-laying version of the PzKpfw IV
 A British destroyer was sunk by a PzKpfw IV 
in the Boulogne harbor, May 23 1940 
The PzKpfw IV hull was a simple design, with high-quality steel plates made by the electric furnace process, and austenitic steel weld joints. Two bulkheads separated the hull into three compartments: driving, fighting and engine. The front driving compartment housed the transmission and final drive assemblies as well as seats for the driver and radio operator/hull gunner. The superstructure was bolted to the top flange of the hull, and the welded turret had sloped sides. The commander's cupola on the back of the turret roof had five observation ports equally spaced around it with the front port pointing directly forward in line with the main gun. 
The main power plant was the standard medium tank engine, the Maybach HL120 TRM, a 12-cylinder liquid-cooled petrol engine. Cooling air entered through louvres on the left hand side of the engine compartment, and was drawn over the engine by two fans. An exceptionally large filter provided clean air for the power plant. Track tension was adjusted by a large diameter idler wheel mounted on an eccentric axle at the rear of the vehicle. the suspension system consisted of fout bogie units per side, each of which was fitted with two rubber-tyred wheels. Quarter elliptic springs were mounted on the underside of the leading axle arm of each bogie. The other end of the spring rested on a shackle pin and roller, carried on an extension of the trailing axle arm. Four support rollers per side completed the suspension.

 
To PzKpfw IV   page 2
To PzKpfw IV   page 2