The initial order was for 900 but that was later increased to 2,700.
In February 1941, Hitler ordered that all PzKpfw IIIs were to have the 50 mm KwK 39 L/60 guns. There were difficulties in getting a supply of them so the army ordnance department continued to use the 50 mm KwK L/42 guns as they felt it would be enough to handle any enemy tank. Once Hitler learned that the shorter gun was being used, he ordered the long version installed and they were starting in December 1941.
Early production had the 50 mm KwK L/42 gun.
Hull was lengthened, and the engine deck received an extension to the rear. Smoke candles had armor added and were moved to below the tail pipe. The driver received a new visor. Hull machine gun mounted in ball-mount. The access hatches in the upper front hull were changed to single piece hatches. Air intakes for the brakes and final-drive cooling were mounted on the upper hull in the front.
From April 1942 there was 20 mm of spaced armor added to the gun mantlet and/or the front superstructure.