The Panzerkampfwagen III Ausführung J1 (Panzer III J1) (Sd.Kfz. Index: Sd.Kfz. 141/1) is an up-gunned modification of the Panzer III J, which is the ninth variant of the Panzerkampfwagen III medium tank family (the "I" variant was skipped). From December 1941, some existing units of the Panzer III J variants were modified with the 50 mm Kampfwagenkanone (KwK) 39 L/60 tank gun to replace the earlier 50 mm KwK38 L/42 tank gun. They were originally known as the Panzer III J1 before being renamed the Panzer III L. Armoured vents were installed on the rear engine deck of tanks going to North Africa. This is somewhat comparable to when the Germans started modifying some of their older Panzer IV Fs with longer KwK40 L/43 guns in early 1942. The new improved Panzer IV F was initially known as the Panzer IV F2, before being redesignated as the Panzer IV G. The original Panzer IV F was then renamed Panzer IV F1.

Introduced in Update 1.43, the Panzer III J1 is an improved variant of the Panzer III J. Armed with the long-barrelled 50 mm KwK39 L/60 tank gun, players will notice a significant increase in firepower over the standard Panzer III J. Dealing with heavier armoured adversaries is much easier, and engagement range is greatly increased. However, with the appearance of early Soviet T-34 medium tanks and early KV-1 heavy tanks in battle, players must be cautious, as these tanks pose a severe threat to the Panzer III J1. Since the long-barrelled 50 mm KwK39 L/60 tank gun will struggle to penetrate Soviet early T-34 medium tanks and early KV-1 heavy tanks beyond close ranges, engagement must be much closer. Finally, the long-awaited electric power traverse system has arrived, addressing the fundamental weakness of the Panzer IIIs that has remained for the previous eight variants.