46 cm/45 Type 94
A Type 94 naval gun being calibrated on Yamato during construction
Type	Naval gun
Place of origin	Japan
Service history
In service	1940–1945
Used by	Imperial Japanese Navy
Wars	World War II
Production history
Designer	C. Hada[1]
Designed	1934
Manufacturer	Kure Naval Arsenal[1]
No. built	~27
Specifications
Mass	147.3 tonnes
Barrel length	21.13 m (69 ft 4 in), 46 calibers
Diameter	46 cm (18.1 in)
Shell	AP Type 91: 1,460 kg (3,218.7 lb) HE Type 0: 1,360 kg (2,998.3 lb) AA Type 3: 1,360 kg (2,998.3 lb)
Calibre	46 cm (18.1 in)
Breech	Welin breech block
Recoil	Hydraulic recoil mechanism
Carriage	Yamato-class battleship
Elevation	+45/-5 degrees. 10°/s
Traverse	300°, 2°/s
Rate of fire	1.5 - 2 rounds/min
Muzzle velocity	780 m/s (2,600 ft/s)
Effective firing range	25 km (16 mi)
Maximum firing range	42 km (26 mi) at 45° elevation

The Japanese 46 cm/45 Type 94 naval gun (四十五口径九四式四〇糎砲, Yonjūgo-kōkei kyūyon-shiki yonjussenchi-hō) was a 46 cm (18.1 in) naval gun, the largest calibre gun to ever be mounted on a warship. Only two ships carried them, the Imperial Japanese Navy's World War II battleships Yamato and Musashi. They were designated as a much smaller 40 cm (16 in) gun in an effort to hide their true size.

The gun was designed in accordance with the prevailing Japanese naval strategy of Kantai Kessen, the Decisive Battle Doctrine, which presupposed Japan would win a war by fighting and winning a single, decisive naval action. Essential to that victory was being able to out-gun and out-fight its adversary. No other ship built could match the firepower and broadside weight of a Yamato-class battleship.

In spite of this, there were no battleship-to-battleship engagements involving either completed vessel of the Yamato-class and an enemy warship. Both were sunk by aerial attack.

Description

The 46 cm (18.1 in) 46 cm/45 Type 94 naval rifle was a wire-wound gun. Mounted in three 3-gun turrets (nine per ship), they served as the main armament of the two Yamato-class battleships that were in service with the Imperial Japanese Navy during World War II. When the turrets and the guns were mounted, each weighed 2,510 tons, 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 most of the very large guns of other navies, they could fire special anti-aircraft shells (Sanshiki), referred to as "beehive".

Construction

Some 27 guns were built for the three battleships of the Yamato class. Only 18 were ever shipped, nine each aboard the Yamato and Musashi; the third vessel of the class, the Shinano, was converted into an aircraft carrier and sunk before it entered combat. The complex Type 94 barrels were constructed in three autofrettaged stages. A half-length tube was fitted over the first tube and shrunk onto it. The assembly was then wire wound and two additional tubes shrunk over the entire length of the gun tubes. A final inner tube was then inserted down the gun and expanded into place. This inner tube was then rifled to finish the gun. As designed, this gun could not cost effectively be relined but instead had to have the entire gun tube replaced due to wear.^[2]

Unlike previous designs the turrets were found to have nothing in common with previous British Vickers designs used in other Japanese battleships when examined by a US naval technical team. Each gun was independently sleeved allowing for separate elevation. The shell hoists and powder rams were found to be ingenious though unduly heavy designs that allowed a relatively rapid rate of reload.^[2] 180 shells (60 rounds per gun) were stored in the turret's rotating structure. The shells were stored vertically and an innovative system of geared mechanical conveyors was employed to move the extremely large and heavy shells from the shell rooms. The mechanical advantage required to move the heavy shells meant these conveyors operated extremely slowly but the 180 shells stored in each turret were considered sufficient for a surface engagement.^[3]

Range and flight time

With Type 91 AP shell

Impact angle and velocity

With Type 91 AP shell

• 
  A Type 1 armour-piercing shell at the Yasukuni Shrine in Tokyo.
• 
  Drawing showing internal structure of Type 91 armour-piercing shell.
• 
  High-explosive Type 0 shell.
• 
  Yamato's 46 cm/45 Type 94 naval gun shells.