This paper model is the Karl-Gerät (040/041) (aka Mörser Karl), a World War II German self-propelled siege mortar (Mörser) designed and built by Rheinmetall, the papercraft is created by lazylife, and the scale is in 1:72.
Karl-Gerät's heaviest munition was a 60 cm (24 in) diameter, 2,170 kg (4,780 lb) shell, and the range for its lightest shell of 1,250 kg (2,760 lb) was just over 10 km (6.2 mi). Each gun had to be accompanied by a crane, a heavy transport trailer, and several modified tanks to carry shells.
Seven guns were built, six of which saw combat between 1941 and 1945. It was used in attacking the Soviet fortresses of Brest-Litovsk and Sevastopol, bombarded Polish resistance fighters in Warsaw, participated in the Battle of the Bulge, and was used to try to destroy the Ludendorff Bridge during the Battle of Remagen. One Karl-Gerät has survived and the remainder were scrapped after the war. For further information please click here.
You can download this paper model template here: WWII German Self-Propelled Artillery 60cm Karl-Gerät Free Paper Model Download