The Gustav Railway Canon, popularly known as Schwerer Gusta was a German 80-centimetre railway gun. It is the largest-calibre rifled weapon ever used in combat and the heaviest mobile artillery piece ever built. According to Wikipedia, The Schwerer Gustav weighed nearly 1,350 tonnes and was capable of firing 4.8 metric ton heavy projectiles at a distance of 47 km with a muzzle velocity of 820 m/s.

Background

In preparation for the Second World War, Adolf Hitler was eager to extend his power into Western Europe. His ambitions included the annexation of France. The French however had fortified their border with Germany. The Maginot Line was an impressive barrier of steel and concrete that for all intents and purposes should've been impenetrable.

In 1934, the German Army High Command (Oberkommando des Heeres (OKH)) commissioned Krupp of Essen to design a gun to destroy the forts of the French Maginot Line. The gun's shells had to punch through seven meters of reinforced concrete or one full meter of steel armor plate, from beyond the range of French artillery.
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