Panzer PzIII German WWII Medium Tank..
The first medium tank developed by Nazi Germany was the Pz. III, which did not enter active service in large numbers until 1939. The Pz. III was initially armed with a 37-mm antitank gun and two machine guns. It weighed about 20 tons, had a top road speed of 25 miles per hour, and carried a crew of five. About 100 Pz. III's fought in the Polish campaign and about 350 in the invasion of France. The need for greater firepower and more protection was apparent by 1941, so newer versions were given a 50-mm gun and fitted with armour 30–50 mm thick. The Pz. III could accommodate these improvements because it had been designed with a larger turret and a 12-cylinder, 300-horsepower engine.

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The 1,500 Pz. III's that took part in the invasion of the Soviet Union in 1941 outfought most Soviet tanks but were in turn completely outclassed by the new Soviet T-34, which had a lethal 76.2-mm gun, sloping armour, and excellent speed and mobility.

Even Pz. III's fitted with a high-velocity 50-mm gun and protected by armour 50–70 mm thick could not cope with the T-34, so the tanks were taken out of service on the Eastern Front, though they continued to fight in the Mediterranean theatre into 1943. By the time production was halted early that year, about 5,660 Pz. III's had been built.

Panzerkampfwagen III (PzKpfw III), more commonly referred to as the Panzer III, was a tank developed in the 1930s by Germany and used extensively in World War II. It was designed to fight other AFVs, serving alongside the infantry-support Panzer IV. It soon became obsolete in this role and for most purposes was supplanted by up-gunned Panzer IVs, though some would continue to be used for infantry support until late in the war.

Development & History of the PZ III Panzer Tank
On January 11, 1934, following specifications laid down by Heinz Guderian, the Army Weapons Department drew up plans for a medium tank with a maximum weight of 24,000 kg and a top speed of 35 km/h. It was intended as the main tank of the German Panzer divisions, capable of engaging and destroying opposing tank forces.

Daimler-Benz, Krupp, MAN, and Rheinmetall all produced prototypes. Testing of the prototypes took place in 1936 and 1937, leading to the Daimler-Benz design being chosen for production. The first Panzer III A came off the assembly line in May of 1937, and a total of ten, two of which were unarmed, were produced in 1937. Mass production of the tank, then in model III F, began in 1939.

Between 1937 and 1940, attempts were made to standardize parts between Krupp's Panzer IV and Daimler-Benz's Panzer III.

Much of the early development work on the Panzer III was a quest for a suitable suspension. Several varieties of leaf-spring suspensions were tried on ausf A through D before the torsion-bar suspension of the ausf E was standardized. The Panzer III, along with the Soviet KV heavy tank, was one of the first tanks to use this suspension design.

The Panzer III was intended as the main battle tank of the German forces. However, it proved to be inferior to the T-34 tank of the Soviet Union and was replaced by an upgunned version of the Panzer IV, which could carry a high-velocity 75 mm gun. Additional frontal armor meant the Panzer III during 1941 and 1942 was impervious to most British and Russian anti-tank guns at all but close ranges when shot at from the front. The sides were still vulnerable to many enemy weapons including anti-tank rifles.

The unusually heavy rear armor of the Panzer III was a weight penalty that was not in line with its combat value. Although several tanks of the early war period had heavy rear armor, in general the design trend during the war was to thin the side and rear armor as much as possible, concentrating heavy armor in the frontal area. For example, the Panther III tank had very heavy frontal armor but thin side and rear armor.

A column of Pz-IIIs advancing across the Russian plain leave a trail of devastation

The Panzer III was intended to fight other tanks and a high-velocity 5 cm gun was initially called for. But the infantry were being equipped with the 3.7 cm anti-tank gun, and it was felt that in the interest of standardization the tanks should carry the same. As a compromise, the turret ring was made large enough to accommodate a 50 mm gun should a future upgrade be required. This single decision would later assure the Panzer III a much prolonged life in the German army.

The Panzer III models A through C were powered by a 230 hp, 12-cylinder Maybach HL 108 TR engine, giving a top speed of 20 mph and a range of 95 mi.

Mobility:
The Panzer III was used in the campaigns against Poland, France, the Soviet Union and in North Africa. Some were still in use in Normandy and Arnhem in 1944. In the Polish and French campaigns, the Panzer III formed a small part of the German armored forces. By the time of the German invasion of the Soviet Union (Operation Barbarossa), the Panzer III was numerically the most important German tank. However, Soviet tank units were mainly composed of the much lighter-armed and armored T-26 and BT tanks. This, along with superior German tactical skill, crew training, and the good ergonomics of the Panzer III all contributed to a rough 6:1 favorable kill ratio for German tanks of all types in 1941.

The Panzer III was a good, but not outstanding, tank in terms of armor, armament and mobility. However, it was well-designed in that it had a three-man turret crew (gunner, loader and commander), leaving the commander free to concentrate on commanding the tank and maintaining situational awareness. Although other medium tanks of the time also had this feature, most tanks of the late 1930s had fewer than three men in the turret crew. These other tanks, which may look impressive on paper, lacked this key element of "fightability".

The French Somua S-35 was a classic example of a tank that appeared to be the equal of the Panzer III on paper, with a good gun and strong armor, but with its one-man turret crew it was hopelessly outclassed by the Panzer III.