The Panzer III was built by Daimler-Benz to the doctrine Heinz Guderian pushed in 1934: a dedicated tank killer working alongside Krupp’s Panzer IV, which carried a short 7.5cm gun for bunkers and infantry. Its biggest edge was a three-man turret that left the commander free to watch the battlefield from a cupola ringed with vision blocks, while the French SOMUA S35 had a one-man turret and early T-34s a cramped two-man turret. In the early stages of Operation Barbarossa in 1941, German tanks achieved a six-to-one kill ratio against older Soviet T-26 and BT tanks. Designers had also built the turret ring larger than the original 3.7cm gun required, anticipating a 50mm weapon.

Against the T-34 and KV-1, the 3.7cm gun failed, and the oversized ring allowed the 5cm KwK 38 and then the longer KwK 39 on the Ausf. J. But the chassis, torsion bars and transmission topped out around 23 tons as armor grew from 15 to 50 millimeters and Schürzen skirts were added on the Ausf. M. The Panzer IV’s larger ring took the long 75mm anti-tank gun, and the final Panzer III, the Ausf. N, received the Panzer IV’s old short 7.5cm gun. By 1943 the turreted tank was out of production and the chassis lived on as the StuG III assault gun, the most produced German armored fighting vehicle of the war, with about 18,000 vehicles built on the Panzer III chassis.

• Japan bought two Panzer IIIs, one with a 50mm and one with a 75mm gun, to reverse engineer, and they were obsolete on arrival.
• The early 3.7cm gun was chosen to share ammunition with the infantry’s 3.7cm anti-tank gun.
• Waterproofed Tauchpanzer IIIs with snorkel hoses were built for Operation Sea Lion and later crossed rivers underwater during the invasion of the Soviet Union.
• Removing the turret let the StuG III carry a bigger gun and thicker front armor while staying under the weight limit.
• At Factory No. 37 in Sverdlovsk, the Soviets rebuilt more than 200 captured Panzer III chassis as the SU-76I with 76.2mm guns.