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The Schwerer Gustav, or Heavy Gustav, was an 80-centimeter German railway gun, the largest caliber rifled weapon ever used in combat and the heaviest mobile artillery piece ever built, at 1,350 tons. It was conceived in the mid-1930s to break the French Maginot Line, whose forts were protected by up to seven meters of reinforced concrete and a meter of steel. Krupp engineer Erich Müller calculated that the job required a 30-meter barrel firing a seven-ton shell. Adolf Hitler visited Krupp in Essen in 1936, the plans were approved in 1937, Krupp delivered the first gun free, and the second, Dora, cost seven million Reichsmarks. Casting the barrel proved so hard that acceptance trials at Rügenwalde slipped to early 1941, long after Germany bypassed the Maginot Line and France surrendered.

The gun rode twin parallel tracks on 40 axles and 80 wheels, and since it could only elevate to 48 degrees, crews aimed it by building curved track. A 25-car train about 1.5 kilometers long carried the parts, and 4,000 men prepared each site, with 250 needing 54 hours to assemble it under the cover of two anti-aircraft battalions. In 1942 it went to the siege of Sevastopol, where a 16-kilometer rail spur was built, and opened fire in June. After 47 combat rounds and about 250 test shots its rifling was worn out and the barrel went back to Essen. Moved near Leningrad, it sat idle when that offensive was canceled. On April 14, 1945, German forces blew it up near Auerbach, and Dora was destroyed near Grafenwöhr on April 19.

• The gun took 30 to 45 minutes per round and could fire about 14 shots a day.
• Five shells knocked Fort Siberia out of action at Sevastopol.
• On June 6, 1942, nine armor-piercing shells destroyed the White Cliff ammunition magazine 30 meters below Severnaya Bay, and the blast sank a boat moored above.
• Its 4.8-ton high explosive shell carried 700 kilograms of explosive and left craters 12 meters wide and 12 meters deep.
• A planned successor, the Langer Gustav, meant to hit London with rocket-assisted shells from 190 kilometers, was damaged by RAF raids before completion.