File:80cm Gustav shell.jpg - Wikimedia Commons

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 Gustav, Wiki

File:DoraSchwererGustav.jpg - Wikimedia Commons

Artillery wagon - Factorio Wiki

The Powder Toy - Schwerer Gustav Rail gun by AviatorGuy

24 cm Theodor Bruno Kanone (E) - Wikipedia

File:Schwerer Gustav Oorlogsmuseum Overloon 5-10-2021 12-19-20.jpg

File:800 mm gun gustav in Soviet Union 1941.jpg - Wikimedia Commons

Gustav Gun - The Largest Gun Ever Built, Page 2

Schwerer Gustav - Hitler's giant gun - How it worked and why it turned out to be a disaster