It was envisaged in the mid-1930s that each German tank battalion would have three companies of relatively light medium tanks and one company of better armed and armoured medium tanks. The former eventually became the Panzerkampfwagen III (PzkPfw III) or SdKfz 141, while the latter became the Panzerkampfwagen IV (PzKpfw IV) which was to remain in production throughout World War II. In 1935 the Weapons Department issued contracts for the construction of prototype vehicles against the lighter concept to Daimler-Benz, Krupp, MAN and Rheinmetall-Borsig. At an early stage it was decided to arm the tank with a 37-mm gun which would fire the same ammunition as that used by the infantry anti-tank gun, but provision was made that the turret ring diameter be large enough to permit the upgunning of the vehicle to 50 mm if this should be required. Following trials with the prototype vehicles the Daimler-Benz model was selected, although the first three production models, the PzKpfw III Ausf A, PzKpfw III Ausf B and PzKpfw III Ausf C were built only in small numbers, differing from each other mainly in suspension details, In September 1939 the vehicle was formally adopted for service, and mass production was soon under way. The PzKpfw III was first used in combat during the invasion of Poland, The next production models were the PzKpfw III Ausf D and PzKpfw III Ausf F, the former with thicker armour and a revised cupola, and the latter with an uprated engine and only six road wheels. In 1939 it was decided to push ahead with the 50-mm model and this entered production in 1940 under the designation PzKpfw III Ausf F. This was followed by the PzKpfw III Ausf G version with similar armament but more powerful engine. For operations in North Africa the vehicles were fitted with a tropical kit, while for the proposed invasion of England a special version for deep wading was developed. The latter were never used for their intended role but some were successfully used during the invasion of the USSR in 1941. The PzKpfw Aus H introduced wider tracks and a number of important improvements.
The 50-mm L/42 gun was inadequate to cope with the Soviet T-34 tank, so the longer-barrelled KwK 39 L/60 weapon was installed. This had a higher muzzle velocity, and vehicles fitted with the weapon were designated PzKpfw III Ausf J. Many vehicles were retrofitted with the 50-mm gun, and by early 1942 the 37-mm version had almost disappeared from front-line service. The next model was the PzKpfw III Ausf L, which had greater armour protection, pushing its weight up to just over 22 tonnes, almost 50 per cent more than the weight of the original prototype. The PzKpfw III Ausf M and PzKpfw III Ausf N were fitted with the 75-mm L/24 gun which had been installed in the PzKpfw IV; a total of 64 rounds of ammunition were carried for this gun. Production of the PzKpfw III was finally completed in August 1943. The chassis was also used as the basis for the 75mm assault gun (Gepanzerte Selbstahrlafette für Sturmgeschütz 7.5 cm Kanone or SdKfz 142), of which a few were used in the invasion of France in 1941; production of improved SP guns on PzKpfw III chassis continued until the end of World War II. Other variants included an armoured recovery vehicle, an armoured observation vehicle (Panzerbeobachtungswagen) and a command vehicle (Panzerbefehlswagen III), A total of 15,000 chassis was produced for both the tank and assault gun applications.
The layout of the PzKpfw III was basically the same in all vehicles, with the driver at the front of the hull on the left and the machine-gunner/radio operator to his right. The three-man turret was in the centre of the hull, the commander having a cupola in the centre of the roof at the rear. The engine was at the rear of the hull, and the suspension, which was of the torsionbar type from the PzKpfw III Ausf E, consisted on each side of six small road wheels, with the drive sprocket at the front and the idler at the rear; there were three track-return rollers.
Specification PzKpfw III Ausf M Crew: 5 Weight: 22300 kg (49,160 lb) Dimensions: length (including armament) 6.41 m (21 ft 0 in);length (hull) 5.52 m (18 ft 1.5 in); width2.95 m (9 ft 8 in); height 2.50 m (8 ft 2.5 in) Powerplant: one Maybach HL 120 TRM 12-cylmder petrol engine developing 300 hp (224 kW) Performance: maximum road speed 40 km/h (25 mph); maximum road range 175 km (110 miles); fording 0.8 m (2 ft 8 in); gradient 60 per cent; vertical obstacle 0.6 m (2 ftO in); trench2.59 m (8 ft 6 in)