46cm/45 Type 94 Main Battery Guns were the largest guns mounted on a warship. The guns were 18.1 Inches (46 centimeters) in diameter, larger than the largest guns mounted on the warships of other navies. The guns were mounted on the Yamato-class battleships, Musashi and Yamato.
The guns mounted on the Musashi and the Yamato were mounted in three triple gun turrets, totaling in nine guns mounted per ship. During World War II, the 46cm guns were purposefully called 40cm/45 Type 94 Naval guns in an effort to deceive other nations into thinking the guns were smaller than their true size. 27 guns were built, with two thirds being lost with Musashi and Yamato.
The effective firing range of the guns were 16 miles (25km) with the maximum range being 26 miles (42km.) Each of the shells shot by the 46cm guns weighed over a ton and a half. Each turret on a Yamato-class battleship weighed about 2,510 tons, a greater tonnage than that of a typical Flecther-class destroyer of the United States Navy. The rate of fire of the guns was 1 to 2 rounds per minute. The muzzle velocity of the guns were around 780 m/s (2600 ft/s)
Sources: Myself, Wikipedia