40 cm/45 Type 94 naval gun

The Japanese "40 cm/45 Type 94 naval gun" (四五口径九四式四〇糎砲) was the largest bore gun ever mounted on any warship. They were actually 46 cm (18.1 in) guns, but were designated 40 cm (15.7 in) in an effort to hide their true size.

Description
The built-up guns were mounted as the main armament of the Yamato-class battleships that were in service with the Imperial Japanese Navy during World War II. The turrets the guns were mounted in weighed 2,510 tons each, which is about the same tonnage as an average sized destroyer of the era.

The Japanese guns were of a slightly larger bore than the three British 18 inch naval guns built during World War I, although the shells were not as heavy. Britain had later designed the N3-class battleship with 18-inch guns but none were built, leaving no Allied naval guns to compare with the Type 94. Unlike the very large guns of other navies they could fire special anti-aircraft shells (Sanshiki) referred to as "beehive".