Basically, the Ausf F was the same vehicle as the Ausf E. In fact, it was the result of an order to mass-produce an effective battle tank. In January 1939, the order was reduced by 250, after production orders had been placed for the improved models, Ausf G and H.
The basic change was to the ignition system. Early in the production run, cast air-intakes were added to the upper hull plate to allow air circulation for brakes and final-drive cooling. The majority were produced mounting the 3.7cm KwK, but approximately 100 were equipped with the 5cm KwK L/42 and external mantlet as original equipment. From August 1940 until 1942, many of the remainder were converted from the 3.lcm KwK to the 5cm KwK L/42 and external gun mantlet. Orders were also issued to up-armour the hull and superstructure, by adding 30mm plates, at the same time as the upgunning took place.
In late 1939 and early 1940, the Ausf F were issued to the Panzer regiments as quickly as they could be produced. On 10 May 1940, 348 Pz Kpfw III, mostly Ausf E and F, but with a few Ausf G, were with seven Panzer divisions on the Western Front. At this time, there were two light tank companies with each tank detachment, but the actual strength varied greatly between the seven Panzer divisions, ranging from five to seventeen Pz Kpfw III in each light tank company. The last Ausf F known to have been in action were with the 116th Panzer Division in June 1944. They are now on display at the Patton Museum at Fort Knox, Kentucky.