The Schwerer Gustav or Heavy Gustav was a large-scale piece of siege artillery developed in Germany beginning in the late 1930s. Adolf Hitler was, at the time, looking for a solution that could defeat the French Maginot line, along the French-German and French-Italian borders. The Maginot line was a 1,500 km-long defensive wall, made up of tanks, concrete fortifications, and machine gun nests. Hitler recruited a German company, the Friedrich Krupp A.G. Company of Essen, to build a weapon that could defeat the Maginot line.
Two years later, in 1941, the Friedrich Krupp A.G. company completed the Gustav Gun, named after the head of the Krupp family. The railway-mounted weapon was the largest gun ever built. Fully assembled, it weighed in at 1,344 tons, was four-stories tall, 20-feet wide, and 140-feet long. It required a 500 man crew to operate it, and had to be moved to be fully disassembled, as the railroad tracks could not bear its weight in transit. It required 54 hours to assemble and prepare for firing.
The bore diameter was just under 3-feet and required 3,000 pounds of smokeless powder charge to fire two different projectiles. The first was a 10,584 pound high explosive shell that could produce a crater 30-feet in diameter. The other was a 16,540 pound concrete-piercing shell, capable of punching through 264 feet of concrete. Both projectiles could be shot, with relatively correct aim, from more than 20 miles away.
The Gustav Gun was used in Sevastopol in the Soviet Union during Operation Barbarossa and destroyed various targets, including a munitions facility in the bay. It was also briefly used during the Warsaw Uprising in Poland. The Gustav Gun was captured by the Allies before the end of World War II and dismantled for scrap. The second massive rail gun, the Dora, was disabled to keep it from falling into Soviet hands near the end of the War.