Orders were given to get the 5cm KwK39 L/60 gun into a production series as quickly as possible which resulted in the Ausf J series being split between this gun and the 5cm KwK L/42. Originally, in August 1940, Hitler had ordered the L/60 gun, but the Ordnance Department did not implement the decision as the L/42 had recently been introduced and had proved successful. At his birthday demonstration in April 1941, Hitler saw the Pz Kpfw III Ausf J still without the long gun and insisted on its fitting as soon as possible. Events in Russia two months later proved the need for a more powerful armament.
The only differences between the Ausf J with the 5cm KwK L/42 and those with the 5cm KwK39 L/60, were the gun itself and the ammunition stowage which was reduced because of the increase in the shell length.
The Ausf J with the long-barrelled 5cm KwK39 L/60 were issued to the five tank detachments formed in early 1942 for the 3rd, 16th, 29th and 60th Motorized Infantry Divisions, and the 5th SS Motorized Infantry Division 'Wiking'. The remainder were used as replacements for the extremely high losses which had been sustained in Russia and North Africa. The long 5cm KwK was very useful in North Africa when engaging the Grant and Valentine tanks, but was of little value in a frontal engagement against a Russian T-34 or KV-1.