The inadequacy of this armament was only fully realised in 1941 after the appearance of the T -34 on the Russian front. This very advanced Russian tank had a shock effect on the leaders of the German Army. While it was still calculated on 17th July 1941 that the raising of a proposed 36 tank divisions would require 7992 Pz Kw IIIs a note dated 29th November 1941 after the introduction of the Russian T-34 shows a complete reversal. At this period doubts were already being expressed as to the efficacy of armoured forces and Hitler had personally described the Pz Kw III as an unsuccessful design. It must however be made clear that for its time this vehicle was extremely advanced and that if Guderian's original demand for a 5 cm long-barrel gun had been met at the outbreak of war the Pz Kw III could have been, in 1940 and 1941, the best fighting tank of all the belligerent powers.
A memorandum dated 21st July 1941 and issued by the Inspector General for Transport stated that additional capacity and manufacturing areas would be made available to extend tank production and that these would include, among others, a Daimler-Benz factory, the Krupp vehicle works, Fross-Bussing in Vienna, Tatra in Kolin, Framo in Hainichen as well as parts of MAN, Henschel, Hanomag, Auto-Union and NSU.
It was thus not until 1941 that the order was given for the introduction of the 5 cm gun (KwK 39) L/60 calibre (barrel length 300 mm) for Pz Kw III. Using the "Panzergranate 40" this weapon produced a muzzle velocity of 1180 mps. Production Pz Kw IIIs so equipped were designated J (Sd Kfz 141/1), type description 8/ZW. In addition all Pz Kw IIIs returned to Germany for general overhaul after April 1941 were refitted with this weapon. In contrast to the 99 rounds which could be carried for the 5 cm gun L/42 only 78 rounds could be stowed for the L/60. Small technical differences distinguished the J version from its predecessors. The reverse gear change, which was secured by a spring-loaded pedal, had been worked by a button with a wire pull, but from the Model J onwards a hand lever was used. The internal expanding brakes too for this and for subsequent models were activated concentrically, whereas formerly an eccentric disc, which fitted under the upper brake shoes, had been used. Levers were introduced to replace the steering pedals which had operated the brakes in earlier models. The total weight of Model J was 21.5 tons and the overall length was increased to 556 mm. On 1st July 1941 a total of 327 Pz Kw IIIs with the 3.7 cm tank gun and 1174 with the 5 cm tank gun were available to the German Army. By 1st April 1942 the number of the 3.7 cm vehicles had fallen to 131, but a total of 1893 machines with the 5 cm gun was now available. The estimated monthly production for January 1942 was scheduled to be 190 machines, but because of delivery problems with the guns and the armoured housings only 159 were in fact built.
This model L (type 9/ZW) was introduced at the end of 1941 and had increased frontal armour on the turret and 20 mm "spaced armour" plates on the mantlet and superstructure front. By increasing the front and the turret front armour to 70 mm, the combat weight was raised to 22.3 tons. The MG ammunition stowage was increased from 2000 to 4950 rounds.
Pz Kpfw III Ausf L mit Waffe 0725. This was an experimental gun based on the Gerlich principle, which involved the use of a tapered-bore barrel of 75/55mm, and a skirted projectile, the skirts of which were squeezed down as the projectile passed along the bore of the barrel, thereby increasing the velocity of the projectile. The rounds used had a core of tungsten-carbide, the shortage of which caused the discontinuance of the experiment.
As an experiment the 0725 gun with a conical barrel was fitted into the Pz Kw III, but because of high barrel wear the promising trials of this weapon could not be continued. The model M (type 10/ZW) which appeared in 1942 had a total weight of 23 tons and the price of this vehicle (without weapons) was RM 96,183. The following totals of Pz Kw IIIs with the 5 cm L/60 gun were produced: 1941-40; 1942- 190; 1943-22. After 1943 Pz Kw III variants were equipped with 5 mm thick side plates, known as aprons or skirt armour to increase protection against hits from anti-tank rifles and hollow-charge ammunition. The aprons, which fitted on to longitudinal rails on both sides of the vehicle, were removable and could be fitted around the turret (Army Technical Pamphlet 1943, No 433). The width of the vehicle, which was first shown on 19th March 1943 in Rugenwalde, was 341 cm. For tank units on the Eastern Front a wider track was issued in 1944 (Army Technical Pamphlet 1944, No 256), the so-called "Ostkette" (literally Eastern track). This was intended to increase the cross-country capabilities of the Pz Kw III and its variants in snow and on soft going. This was simply a makeshift, for the track with its extension on one side could only be used with safety in flat country. The width with the Ostkette fitted was 326 cm.