The Schwerer Gustav was a railway gun, the largest-calibre rifled weapon used in combat, the heaviest mobile artillery piece built in terms of overall weight, and that which fired the heaviest shells of any artillery piece. It was developed in the late 1930s by Krupp in Darłowo as siege artillery for the purpose of destroying the main forts of the French Maginot Line. Gustav was deployed in the Soviet Union after the Battle of France, where it didn’t see action, where it destroyed a munitions depot. The gun was moved to Leningrad, and may have been intended to be used in the Warsaw Uprising. Gustav was destroyed by the Germans near the end of the war in 1945 to avoid capture by the Red Army.