The Panzer III, or Mark III as it was referred to by its British opponents was the mainstay of the German panzer divisions for much of the war. In one form or another it was built and served throughout the 1939-1945 period, as did its larger stablemate, the Panzer IV.
First prototypes were produced in 1936-1937 and the design submitted by Daimler-Benz was selected for production. In common with German pre war practice, the first derivatives were produced in small numbers and used to test out various mechanical options, notably suspension systems.
Some of these saw action early in the war, although in such small numbers that the value of this was solely to gain practical experience. The first of the developments to go into series production was the Ausführung E, with torsion bar suspension and the 3.7cm KwK L/46.5. Nevertheless these were still only produced in small numbers as active service led to continuous upgrades to the armour and armament.
The principal, and final armament upgrade was the substitution of the 3.7cm gun by the 5cm KwK L/42 and later, higher powered versions. Production continued up to late 1943, with the final version (Ausführung N) reverting to the short-barrelled 7.5cm gun for close support work. By this time the Mark III had been totally superseded as a battle tank.
But this was not the end of the Panzer III story.
The basic chassis was proven and reliable, so it formed the basis of the totally new class of AFV called Assault Guns or Sturmgeschütz. Developed according to von Manstein’s recommendation in 1935, these rugged, simple AFVs became an ever more important part of the German armoured forces as the war progressed and German fortunes waned. Removing the rotating turret meant that the vehicle was simpler and cheaper to build, and could carry guns larger than the 5cm KwK. Experience in Russia led to the incorporation of the 7.5cm KwK L/43 and then the L/48. These continued in production up until March 1945. After the cessation of production of the Mark II, the chassis continued to be produced exclusively for Sturmgeschütz.