Like an Aryan Death Star, the Nazis' Gustav was the largest gun ever built and didn't leave much planet where it hit.
In 1939, Adolf "Baby Dick" Hitler needed to figure out how to get past the French Maginot line, a 1500km defensive wall of fortifications, tank barriers, artillery and machine gun nests running along the French-German and French-Italian borders. Before he figured out to simply run around the line via Belgium, Hitler schemed to destroy it outright. To that end, he recruited the Friedrich Krupp A.G. company of Essen, Germany to build him a weapon capable of doing so. By 1941, the Krupp company had designed and built the largest gun of all time, the "Gustav Gun."
Named after the head of the Krupp family, Gustav Krupp von Bohlen und Halbach, the Gustav Gun weighed in at a massive 1344 tons, so heavy that even though it was attached to a rail car, it still had to be disassembled before moving so as to not destroy the twin set of tracks as it passed over. This four-storey behemoth stood 4.5m wide and 43m long. Its 500-man crew, commanded by a Major-General (that's two stars), needed nearly three full days (54 hours, to be exact) to set it up and prep for firing. But when it did fire, whoowhee, hold on to your hat.
The Gustav had a bore diameter of 800mm (just under a yard) and used 1360kg, more than a ton, of smokeless powder charge to fire its two primary shell types: a 4800kg high explosive (HE) shell and a 7500kg concrete-piercing shell - roughly the weight of an unladen 71-passenger school bus, travelling at 823m/s.
With a maximum elevation of 48 degrees, the HE shell could hit a target 47km away, while the bunker-buster could nail anything within 37km - both with reasonable accuracy. The Gustav could basically fire a shell over the widest point of Long Island, New York, and hit nothing but water. If it did hit, the HE would leave a 9m deep crater while the piercing round could penetrate as much as 80m of reinforced concrete (or height of the Seattle Exchange Building).
The Gustav, luckily, saw only very brief action. It fired 300 shells on Sevastopol (at a rate of about 14 shells a day) and 30 more during the Warsaw Uprising of 1944 before being captured by Allied troops and chopped up for scrap. Its seven million Deutsch Mark sister, the Dora, was destroyed by the Germans themselves to keep it from falling into the hands of the Russians. The rest of the Nazis' evil War Machine would fall by 1945 after Allied forces finished curb stomping them back across the Rhienland.
Monster Machines is all about the most exceptional machines in the world, from massive gadgets of destruction to tiny machines of precision, and everything in between.