3d model pak 3 7 cm - PaK 3.7 cm Panzerabwehrkanone 36 German anti-tank gun WWII by De Espona

The PaK 36 (Panzerabwehrkanone 36) was a German anti-tank gun that fired a 3.7cm calibre shell. It was developed in 1936 by Rheinmetall and first appeared in combat that year during the Spanish Civil War. It formed the basis for many other nations' anti-tank guns during the first years of World War II. The KwK 36 L45 was the same gun but was used as the main armament on several tanks, most notably the early models of the Panzer III.

The PaK 36, being a small-calibre weapon, was outdated by the May 1940 Western Campaign, and crews found them all but useless against heavy allied tanks like the British Mk.II Matilda and the French Char B1 and Somua S35. A group of these guns claimed to have knocked out a Char by firing at its flank, but this is most likely made up. The poor performance against heavy enemy armour resulted in the PaK 36 being dubbed the 'Door Knocker'.