24 cm Theodor Bruno Kanone (E) - Wikipedia

Krupp 80 cm Kanone Schwerer Gustav (Dora) Railway Gun

Trivia: Gustav Max was based on Schwerer Gustav, the rail cannon made and used by the nazi germany, also considered the largest gun ever used in a war. : r/DuelLinks

Schwerer Morpho : r/EightySix

Dora/Schwerer Gustav K. (E) Rail Gun, World War II Wiki

Where is Schwerer Gustav (an 800 mm German railway gun) now? - Quora

SimplePlanes Schwerer Gustav

Which modern gun can outmatch the WW2 800mm Schwerer Gustav? - Quora

Heavy Gustav, World Conqueror 4 Wiki

File:Dora WTS.jpg - Wikimedia Commons

Schwerer Gustav 800 mm supergun firing position of 1942