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.
Due to the introduction of the upgunned and uparmoured Panzer IV, the Panzer III was, after the Battle of Kursk, relegated to secondary roles, such as training, and it was replaced as the main German medium tank by the Panzer IV and the Panther. The Panzer III chassis was the basis for the turretless Sturmgeschütz III assault gun, one of the most successful self-propelled guns of the war, and the single most-produced German armored fighting vehicle design of World War II.
The Panzer III was used in the campaigns against Poland, France, the Soviet Union and in North Africa. A handful were still in use in Normandy, Anzio, Finland and in Operation Market Garden in 1944.