One of Mutsu’s salvaged 16″/45 guns outside the Kure Maritime Museum in Kure, Japan. From my trip to the museum in 2015.

Caveat: The information contained in this post is of a very general nature. More detailed (read: technical) information can be found in the U.S. Naval Technical Mission to Japan or on the excellent website (see references section). This post focuses on the 16″ naval guns and is not an overall evaluation of the Nagato-class battleships.

Let’s examine the guns of the Nagato-class battleships and the first 16″ guns to be mounted aboard a battleship.


According to the U.S. Naval Technical Mission to Japan (1946), both of the guns and the mounts were designed by Admiral I. Muto in 1918 and 1919, respectively. Around 16 mounts were constructed (U.S. Naval Report O-47 (N), 1946, p. 22). About 40 guns were manufactured, either at Kure or Muroran Iron works. Six guns, mounted in twin turrets, were purposed as coastal defense guns for the southern entrance to the Sea of Japan. These turrets were mounted on the islands of Iki and Tsushima, as well as at Pusan, Korea (Campbell, 1985, p. 181).

Upon their commissioning in 1920 and 1921, the Nagato and Mutsu were the first battleships in the world to carry 16″ guns. Since the guns fired a heavier shell, the original plan of twelve guns was reduced to eight. The guns were arranged in four twin turrets with turrets #2 and #3 superfiring (Stille, 2013, p. 127). Prior to their cancellation under the Washington Naval Treaty, these guns were also intended to be mounted on the Kaga, Tosa, Amagi, Akagi, Takao, Atago, Kii, Owari, Suruga, and Omi (Campbell, 1985, p. 181). The Amagi was heavily damaged during the Great Kanto Earthquake in 1923 and was scrapped, while the Kaga and Akagi were converted to aircraft carriers.

There are multiple early designs of the Yamato-class which note a main battery of 16.1″/45. Garzke and Dulin (1985) note that the Japanese briefly considered using the 16.1″/45 guns on the Yamato-class battleships, but they were expecting to fight more enemy ships at longer ranges than European battleships. Eventually, the 18.1″ guns were chosen over the 16.1″ due to their greater performance characteristics (p. 88).

Gun Characteristics

Ship Class Used On:Nagato-class battleships
Date In Service: 1921
Gun Weight: 100 tons (102,000 kg) w/breech
Gun Length (overall): 741.73 in (18.84 m)
Bore Length: 720.24 in (18.294 m)
Twist:uniform RH 1 in 28
Chamber Volume:~28,505 cu in (467.11 cu dm)
Rate of Fire:1.5-2.5 rounds/minute
Nagato class battleship (1:100 scale) at the Kure Maritime Museum.

The guns were similar in construction to the British 15″/42 caliber Mark I and lighter in weight. They were wire-wound, although possibly not for their full length given that the external diameter of their muzzle was an inch less than the British 15″ Mark I. The breech was a Welin screw-type with an Elswick 3-motion short arm mechanism that resembled the British 18″ guns of WWI (Campbell, 1985, p. 181).

Mount Characteristics

Weight:1,004 tons (1,020 mt)
Elevation:-5 to +30 degrees (originally), -3 to +43 degrees (modernized), -2 to +35 (coastal defense guns)
Elevation Rate:5 degrees/second
Train:About -130 to +130 degrees
Train Rate:3 degrees/second
Loading Angle:+3 degrees
Armor Thickness:(on new turrets) 18.1″ face; 11″ side; 7.5″ rear; 9.8″ – 9″ roof
Nagato in 1924.
A view of the Nagato’s bow turrets.

Much like the guns and turrets on the Kongo, Ise, and Fuso-class battleships, the turrets for the 16.1″ guns resembled the British 15″ Mk. 1 mountings used on the Queen Elizabeth and Royal Sovereign-classes (U.S. Naval Report O-47 (N), 1946, p. 24).

The turrets were powered from a hydraulic ring main and the training gear worm drive suffered from wear. Elevation on the guns was done by a cylinder and piston attached to the rear of the slide. The rammers were mounted on a continuation of the gun slides and the guns could be loaded at any angle up to 20 degrees. A double longitudinal bulkhead separated the guns in the turrets and also the working chamber where the shells and charges were transferred from the lower to the upper hoists. The shell handling rooms were situated above the powder magazines. The gun loading cage was offset from the gun bore so that it could pivot around a horizontal axis. The powder was separated from the shell in a flash-tight compartment. This rotating loading cage thus allowed the shell and powder to be rammed without having to move the cage in the hoist. It simply rotated to bring each into line with the bore (Campbell, 1985, p. 182).

(U.S. Naval Report O-47 (N), 1946, p. 26)

While the turrets were technically known as “any angle loading turrets,” the guns were never loaded at elevations greater than 20 degrees and the breech could not be opened at elevations above 25 degrees. Reportedly, there were serrations on the compression slope of the gun to grip the driving band of the shell when it was loaded at high angles to prevent the shell from slipping backward, however, these serrations were not verified when the Allies inspected the captured Nagato due to poor lighting (Yes, that’s the actual reason given.) (U.S. Naval Report O-47 (N), 1946, p. 25 – 27).

Ammunition Types

Projectile Types & Weights:Type 88 APC: 2,205 lbs (1,000 kg) (pre-WWII shell)
Type 91 APC: 2,249 lbs (1,020 kg)
Type 0 Common HE: 2,069 lbs (938.5 kg)
Type 3 Common AA: 2,072 lbs (940 kg)

Illumination B-1: N/A
Bursting Charge:Type 91 APC: 32.8 lbs (14.89 kg)
Type 0 Common HE: 97.7 lbs (44.3 kg)
Type 3 Common AA: N/A
Projectile Length:Type 91 APC: 68.4 in (173.85 cm)
Type 0 Common HE: 55.1 in (140 cm)
Type 3 Common AA: 70 in (177.8 cm)
Propellant Charge:494 lbs (224 kg) (pre-WWII)
483 lbs (219 kg) in four bags
Muzzle Velocity:Type 88 APC: 2,592 fps (790 mps)
Type 91 APC: 2,559 fps (780 mps)
Type 0 Common HE: 2,641 fps (805 mps)
Type 3 Common AA: 2,641 fps (805 mps)

Illumination B-1: 2,297 fps (700 mps)
Working Pressure:19-19.5 tons/sq. in (3,000-3,070 kg/sq. cm)
Barrel Life:About 250-300 rounds
Ammo stowage/gunAbout 90 rounds
A display of shells in the Large Exhibits Room of the Yamato Museum in Kure, Japan. I have labelled the shell types. The 4th shell from the left is a 16″ shell that would’ve been fired by a 16″/45 gun.

The Type 91 AP Shell

(Photo Credit: U.S. Naval Technical Mission to Japan Report O-19 “Japanese Projectiles General Types”, p. 31.)

The Type 91 armor piercing shell was manufactured in multiple different calibers and all were painted white with an orange band indicating the center of gravity. The red and green tip on the windshield indicates that the projectile is base-fuzed. The 16″ Type 91 projectiles had a fuze delay of 0.4 seconds which would be triggered upon impact with the water and allow time for the shell to impact the target (U.S. Naval O-19, 1946, p. 32). In order for the ships to visually identify the fall of their AP shells, each had a specific color of dye bag that would color the shell splashes. Pink dye was assigned for the Nagato and black dye was assigned for the Mutsu (DiGiulian, 2020, para. 17).

David Evans and Mark Peattie (1997) write that the Type 91 shell stemmed from firing tests on the incomplete battleship Tosa in 1924. From these tests the Japanese came upon the concept of underwater shots ( 水中弾 suichudan). During the gunnery tests, it was discovered that 16″ shells fired at 20,000 meters, entering the water at an angle of 17 degrees, and 25 meters short of the target would penetrate the hull below the armor. Further testing showed that a shell with a flat head could enter the water at 17 degrees as far as 80 meters from the target and still penetrate. Best results were shown to be at a distance of 40 meters from the target (p. 263).

The Type 91 shell was designed to be dual-purpose. It was capped to penetrate in the event of a direct hit. In the case of impacting the water short of the target, the windshield of the shell was designed to break off exposing the flat cap head and allowing the shell to maintain its trajectory through to water to the target and penetrate the hull underneath the belt armor. In line with the design of the shell, the Japanese fire control doctrine stressed shots falling just short of the target, if not achieving direct hits. It was also believed that if the shell passed underneath the target, the time-delay fuze would still allow it to detonate underneath the keel (Evans & Peattie, 1997, p. 263). There has been skepticism by experts with regard to whether or not the idea of underwater shots would have been very effective. Due to the top-secret nature of the shell and its use, underwater shots were never practiced in peacetime training. Furthermore, the shells were only effective at a range of about 20,000 meters and there were few gun battles historically which occurred at those ranges. Whether or not American intelligence was aware of the Type 91, U.S. battleships following the North Carolina-class were designed to resist underwater hits (Evans & Peattie, 1997, p. 263 – 266). Report O-19 of the U.S. Naval Technical Mission (1946) concluded that the Japanese “sacrificed the effectiveness of their AP projectiles on occasions of direct hitting (particularly against light armor) in order to achieve a doubtful hit through the water or a mining effect for which an AP projectile is singularly poorly designed.” (p. 1)

The Type 0 Common HE Shell

(Photo Credit: U.S. Naval Technical Mission to Japan Report O-19 “Japanese Projectiles General Types”, p. 10.)

Report O-19 of the U.S. Naval Technical Mission to Japan (1946) notes that there was nothing very unique to the Type 0 Common HE shells. The differences between the different calibers were the manufacturing requirements and available machinery. These shells were normally painted maroon in color and given timed fuzes for anti-aircraft use (p. 7 – 9).

The Type 3 Common Shell

Diagram of the Type 3 Common AA shell
(Photo Credit: U.S. Naval Technical Mission to Japan Report O-19 “Japanese Projectiles General Types”, p. 14.)

Many Japanese warships were equipped with a particular type of anti-aircraft shell for their main guns known as the Type 3 Common shell (三式焼霰弾 literally: Type 3 “burning hail” shell). The Type 3 shells for the 16.1″/45 guns had more than 700 tubes filled with an incendiary mixture. These had a time mechanical fuse and were designed to burst approximately 0.5 seconds after exiting the muzzle creating a 20-degree cone of flaming material. The incendiary material burned at approximately 3,000 degrees Celsius for five seconds and created a five-meter-long flame (U.S. Naval O-19, 1946, p. 8 – 14).

The Illumination B-1 Shell

Diagram of the Illumination B Shell. Note that this was only used on guns up to 36cm in caliber. The 40cm guns used the B-1 variant which was likely very similar to this apart from being a single emission type. (Photo Credit: U.S. Naval Technical Mission to Japan Report O-19 “Japanese Projectiles General Types”, p. 22.)

Battleships could be equipped with shoumeidan (照明弾 literally: illumination shells) to give them an advantage during long-ranged night combat. These were developed as a temporary expedient solution to the fact that Allied vessels possessed superior radar. The B shell was developed from the A variant which were simply star shells without a parachute. The B variant was a double emission illumination shell while the B-1 variant was a single emission. The B-1 shell had a maximum range of 24,200 yards and emitted 55,120 candle power (U.S. Naval O-19, 1946, p. 20).

Range & Armor Penetration

Note on Armor Penetration Values:

Garzke and Dulin (1985) derived the penetration values from “a detailed U.S. Navy empirical equation” modeled against U.S. Class B Homogeneous armor. The values are noted as not being precisely correct but should give an accurate measure of performance (p. 495). For a further examination of the Garzke and Dulin data, see the following article: The Garzke and Dulin Empirical Formula for Armor Penetration.

  • Shell Type & Weight: Type 91 APC 2,249 lbs (1,020 kg)
  • Muzzle Velocity: 2,559 fps (780 mps)
RangeElevationStriking VelocityAngle of FallArmor Penetration
5,470 yds (5,000 m)2.5 deg.2,247 fps (685 mps)3.4 deg.
10,940 yds (10,000 m)5.7 deg.2,001 fps (610 mps)7.5 deg.
16,400 yds (15,000 m)9.2 deg.1,768 fps (539 mps)11.8 deg.
21,872 yds (20,000 m)13.5 deg.1,624 fps (495 mps)17.5 deg.10.6″ (269 mm)
27,340 yds (25,000 m)18.8 deg.1,526 fps (465 mps)24.5 deg.
32,808 yds (30,000 m)25.5 deg.1,516 fps (462 mps)34 deg.8″ (203 mm)
41,995 yds (38,400 m)43 deg.
(Range data from Campbell, 1985, p. 181. Armor penetration data from Garzke & Dulin, 1985, p. 89. Blank spaces indicate no data available.)


Due to the IJN’s propensity for hoarding their battlewagons for the decisive battle, the Nagato and Mutsu rarely saw any combat despite participating in several operations. On 8 June 1943, while at anchor at Hashirajima, Mutsu‘s #3 turret magazine exploded. The explosion broke the ship in half and killed 1,121 of the crew. While the actual cause of the explosion forever remains a mystery, some speculate that it could have been caused by a faulty Type 3 Common shell, but tests have ruled that out. The Navy performed a perfunctory investigation, and probably out of convenience, placed the blame on a disgruntled crew member who was facing theft charges (Stille, 2013, p. 129 -130). Conversely, the commander of the First Fleet, Admiral Shimizu Mitsumi was aboard the Nagato and witnessed the explosion, noting that it had the color characteristic of the detonation of the Type 3 Common shells (Prados, 1995, p. 477 – 478). Whatever the cause, this ended the career of the Mutsu, although some of her guns were salvaged (as seen in the above photos).

The only time that the Nagato fired her main battery at an enemy was during the Battle Off Samar during the Battle of Leyte Gulf. As part of Admiral Kurita’s Center Force, the Nagato came upon the escort carriers, destroyers, and destroyer escorts of Taffy 3. Opening fire at a range of 20 miles, Nagato only marginally contributed to the battle by firing 45 shells from her main batteries and 92 shells from her secondary batteries before being forced to retire. Nagato claims to have damaged a cruiser, but it was most likely a destroyer since no American cruisers were present (Stille, 2013, p. 130-131). However, Nagato‘s gunner officer, Commander Inouye Takeo, says that he observed a hit on a carrier with the first salvo from the main battery at 7:01 am. Later on, at around 7:15, the Nagato engaged a destroyer with her 16″ guns (Prados, 1995, p. 670 – 671).

At the end of the day, there’s not much to say about these guns because there’s not much written about them apart from their technical specifications. They’re most notable simply for being the first 16″ guns mounted aboard a battleship. Unfortunately, the data on their armor penetration capabilities is extremely sparse. However, if the numbers are accurate, a comparison with later 16″ guns, such as the U.S. 16″/50 Mk. 7, shows that the Japanese 16.1″/45 3rd Year Type guns were greatly inferior in terms of armor penetration (unfortunately, only two values are given for the Japanese gun). This may be due to older technology, different ballistic properties, and a smaller propellant charge used in the Japanese gun. Whatever the case, these guns were pretty old by the time WWII rolled around.


Evans, D.C. & Peattie, M.R. (1997). Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy 1887-1941. Naval Institute Press.

Campbell, J. (1985). Naval Weapons of World War Two. Naval Institute Press.

DiGiulian, T. (2020). 41 cm/45 (16.1″) 3rd Year Type. Navweaps.

Garzke, W.H., & Dulin, R.O. (1985). Battleships: Axis and Neutral Battleships in World War II. Naval Institute Press.

Prados, J. (1995). Combined Fleet Decoded: The Secret History of American Intelligence and the Japanese Navy in World War II. Naval Institute Press.

Stille, M.E. (2013). The Imperial Japanese Navy in the Pacific War. Osprey Publishing.

U.S. Naval Technical Mission to Japan. (1946). Report O-19: Japanese Projectiles General Types.

U.S. Naval Technical Mission to Japan. (1946). Report O-47 (N) – 1: Japanese Naval Guns and Mounts, Article 1 – Mounts Under 18″.