https://militaryhistorynow.com/2017/05/07/the-great-wall-of-france-11-remarkable-facts-about-the-maginot-line/
https://www.businessinsider.com/6-largest-guns-ever-used-in-combat-2017-9
https://militaryhistorynow.com/2017/05/07/the-great-wall-of-france-11-remarkable-facts-about-the-maginot-line/
https://animals.sandiegozoo.org/animals/elephant
https://www.youtube.com/watch?v=Hf3fgfHoTOc
https://en.wikipedia.org/wiki/Maginot_Line
https://medium.com/war-is-boring/a-nazi-war-train-hauled-the-biggest-gun-ever-made-a05e20070ebd
https://www.tracesofwar.com/sights/12982/Sector-Sevastopol---Fort-Stalin.htm
http://html2.free.fr/canons/dora.htm (Google translate used.)
https://www.tracesofwar.com/sights/12996/Sector-Sevastopol---Fort-Molotov.htm
https://ww2db.com/weapon.php?q=A89
https://interestingengineering.com/schwerer-gustav-the-biggest-cannon-during-wwii