Designed as an infantry-support tank, the Panzer IV was not originally intended to engage enemy armor—that function was performed by the lighter Panzer III. However, with the flaws of pre-war doctrine becoming apparent and in the face of Soviet T-34 tanks, the Panzer IV soon assumed the tank-fighting role of its increasingly obsolete cousin. It was the most widely manufactured and deployed German tank of the Second World War.
Robust and reliable, it saw service in all combat theaters involving Germany and has the distinction of being the only German tank to remain in continuous production throughout the war, with over 8,800 produced between 1936 and 1945. Upgrades and design modifications, often made in response to the appearance of new Allied tanks, extended its service life. Generally these involved increasing the Panzer IV's armor protection or upgrading its weapons, although during the last months of the war with Germany's pressing need for rapid replacement of losses, design changes also included retrograde measures to simplify and speed manufacture.
In Setember 1939, and production of the Ausf. D started. This variant, of which 248 vehicles were produced, reintroduced the hull machine gun and changed the turret's internal gun mantlet to an external one. Again protection was upgraded, this time by increasing side armor to 20 mm (0.79 in). As the German invasion of Poland in September 1939 came to an end, it was decided to scale up production of the Panzer IV (Sonderkraftfahrzeug 161 / Sd.Kfz. 161).