41 cm/45 (16.1") 3rd Year Type
40 cm/45 (16.1") 3rd Year Type
Updated 30 June 2012

These were the first large-caliber guns designed entirely in Japan.  They were mounted afloat only on the Nagato class, but had been planned for use on the Kaga, Amagi and Kii classes of the early 1920s, all of which were canceled as a result of the Washington Naval Limitation Treaty.  Those completed guns and mountings intended for the canceled ships were then used for the modernization of the Nagato class during their 1930s rebuilds.  One of the old turrets removed from Mutsu was installed as a static display at the Japanese Naval Academy at Etajima.  Three twin turrets originally intended for Akagi and Tosa were instead used as coastal artillery, covering the southern entrance to the Sea of Japan on Tsushima, Ikishima and at Pusan, Korea.

These guns were generally similar to British wire wound guns of the time but were of lighter construction, being about an inch (25 mm) less in diameter at the muzzle than the 15"/42 (38 cm) Mark I.  This may indicate that they were not wire wound over their full length.  Used a Welin screw breech but with an Elswick 3-motion short-arm mechanism, which resembled that used on the British 18"/40 (46 cm) guns of 1917.  The breech block needed to be withdrawn straight back into the carrier before it could be swung.  A total of about 40 guns were manufactured at the Kure and Muroran Ironworks.

Mutsu was destroyed by a main magazine explosion on 8 June 1943.  The Japanese attempted to salvage the wreck both during and shortly after the war but it was not until 1970 that a successful effort was begun.  Two guns recovered from Turret 3 are now displayed at the Yamato Museum in Kure and at the Museum of Maritime Science in Tokyo.

Originally designated as 41 cm/45 3rd Year Type.  Redesignated as 40 cm/45 3rd Year Type on 29 March 1922.  Actual bore diameter was 41.0 cm (16.14 inch).

Some of the APC shells for these guns were converted into aircraft bombs and then designated as Type 99 (Model 1939) No 80 Mark 5.  It is believed that one of these destroyed USS Arizona BB-39.  In 1942 the design was modified and bombs built to this new design were designated as Type 2 (Model 1942) No 80 Mark 5 Model 1.


Bow Turrets of Battleship Nagato

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Gun Characteristics
Designation 41 cm/45 (16.1") 3rd Year Type (Model 1914)
40 cm/45 (16.1") 3rd Year Type (Model 1914)
Ship Class Used On Nagato, Kaga, Amagi and Kii Classes
Date Of Design 1914
Date In Service 1921
Gun Weight 100 tons (101.6 mt)
Gun Length oa 741.7 in (18.840 m)
Bore Length 720.24 in (18.394 m)
Rifling Length 615.3 in (15.629 m)
Number Of Grooves (84) 0.161 in deep x 0.345 in (4.1 mm x 8.754 mm)
Lands 0.259 in (6.58 mm)
Twist Uniform RH 1 in 28
Chamber Volume 28,505 in3 (467.11 dm3)
Rate Of Fire 1.5 - 2.5 rounds per minute

1) Firing cycle was 21.5 seconds at low elevations, which probably means at the loading angle of +3 degrees.

2) US Naval Technical Mission to Japan report O-54(N) states that guns meant to be loaded at high elevations had "ridges around the compression slope, to aid in gripping the projectile rotating bands and prevent the projectile from slipping back after seating."

3) The post-war US survey of Japanese Seacoast Artillery states that the coastal artillery turrets could fire 1 round per gun per minute.

Type Bag
Projectile Types and Weights
(see Notes 1 and 2)
Prior to World War II
   APC Type 3 - N/A, but probably 2,205 lbs. (1,000 kg)
   APC Type 5 - 2,205 lbs. (1,000 kg)
   APC No. 6 / Type 88 - 2,205 lbs. (1,000 kg)

World War II
   APC Type 91 - 2,249 lbs. (1,020 kg)
   Common Type 0 HE - 2,069 lbs. (938.5 kg)
   Common Type 3 IS - 2,072 lbs. (940 kg)
   Illum - N/A

Bursting Charge APC Type 91 - 32.8 lbs. (14.89 kg)
Common Type 0 HE - 97.7 lbs. (44.3 kg)

Others - N/A

Projectile Length APC Type 91 - 68.4 in (173.85 cm)
Common Type 0 HE - 55.1 in (140 cm)
Common Type 3 IS - 70 in (160 cm)

Others - N/A

Propellant Charge World War I:  494 lbs. (224 kg)

World War II:  483 lbs. (219 kg) 102 DC1 or 110 C2

Muzzle Velocity APC Type 3 - N/A, but probably 2,592 fps (790 mps)
APC Type 5 - 2,592 fps (790 mps)
APC Type 6 / Type 88 - 2,592 fps (790 mps)

APC Type 91 - 2,645 fps (806 mps) [new gun]
APC Type 91 - 2,559 fps (780 mps) [average gun]
Common Type 0 HE - 2,641 fps (805 mps)
Common Type 3 IS - 2,641 fps (805 mps)
Illum - 2,297 fps (700 mps)

Working Pressure 19 - 19.5 tons/in2 (3,000 - 3,070 kg/cm2)
Approximate Barrel Life 250 - 300 rounds
Ammunition stowage per gun About 90 rounds

1) IS is my abbreviation for the incendiary shrapnel round (sankaidan) intended for AA use.  Fuzes were usually set on the waiting tray in the working chamber.

2) The APC Type 3 was adopted in 1917.  This was superseded by the APC Type 5 which was adopted on 15 June 1925 and was in turn superseded by the APC No. 6 which was adopted on 17 November 1928.  APC No. 6 was essentially similar to the Type 5 in terms of armor penetration but was better protected from premature detonation and had enhanced underwater performance.  APC No. 6 was redesignated as the Type 88 on 6 April 1931.  On that same date, the improved APC Type 91 was adopted.  By World War II, APC Type 5 was only used by the coastal artillery units.  Dye was introduced in 1941 and Type 91 shells containing it were designated as Type 1.

3) Type 91 shells were all 6 / [infinity] crh with boat tail and two copper driving bands.  The diameter of the bourrelet was 16.11 in (40.919 cm).  AP Cap, cap head and windshield together weighed 358 lbs. (162.4 kg).

4) The propellant charge was in four bags.  Bags had a single 8.8 oz (250 gm) black powder igniter patch.

5) The Shômeidan B1 Illumination round had an illuminating power of 5.3 million candelas.  The maximum ballistic range was 24,900 yards (22,770 m).

With 2,249 lbs. (1,020 kg) APC
Striking Velocity
Angle of Fall
2.5 degrees
5,470 yards (5,000 m)
2,247 fps (685 mps)
5.7 degrees
10,940 yards (10,000 m)
2,001 fps (610 mps)
9.2 degrees
16,400 yards (15,000 m)
1,768 fps (539 mps)
13.5 degrees
21,870 yards (20,000 m)
1,624 fps (495 mps)
18.8 degrees
27,340 yards (25,000 m)
1,526 fps (465 mps)
25.5 degrees
32,810 yards (30,000 m)
1,516 fps (462 mps)
43.0 degrees 
(max elevation
of turret)
42,350 yards (38,725 m)
Elevation With 2,069 lbs. (938.5 kg) HE
Range @ 43.0 degrees 33,930 yards (31,025 m)
Aircraft Bombs
Type 99 (Model 1939) No 80 Mark 5
Type 2 (Model 1942) No 80 Mark 5 Model 1
Bursting Charge
49.4 lbs. (22.4 kg) TNA
78.7 lbs. (35.7 kg) TNA
Total Weight
1,757 lbs. (796.8 kg)
1,788 lbs. (811.2 kg)
Length oa
92.6 in (235.1 cm)
91.7 in (233.0 cm)
16.1 in (40.9 cm)
15.9 in (40.4 cm)
Nose thickness
19.17 in (48.7 cm)
11.97 in (30.4 cm)

1) These bombs were rated as being able to penetrate 5.9 inches (15 cm) of armor plate.  Height for this performance is not available but was probably around 10,000 feet (3,000 m).

2) An aluminum plug was used between the burster and the cap as a shock absorber.

3) Both types had two base fuzes to ensure detonation.

Mount / Turret Data
Designation Two-gun Turrets
   Nagato (4), Kaga (5), Amagi (5) and Kii (5)
Weight 1,004 tons (1,020 mt)
(see Note 1)
Original design:  -5 / +30 degrees

Nagato class as modernized:  -3 / +43 degrees

Coastal Defense turrets:  -2 / +35 degrees

Rate of Elevation 5 degrees per second
Train about +/- 130 degrees
Rate of Train 3 degrees per second
Gun Recoil N/A
Loading Angle
(see Note 2)
Original:  -5 to +20 degrees
As rebuilt:  +3 degrees

1) The turrets intended for the canceled ships had improved protection and were somewhat larger and roomier than the earlier ones used on the Nagato class.  For that reason, when the Nagato class were modernized during the mid-1930s, they were then given turrets taken from the unfinished battleships Kaga and Tosa.  The elevation of these later mountings was increased by deepening the gun wells and lowering the revolving structure further down into the ships.  The original Nagato class turrets had sighting hoods on the roof of the turrets while the later ones had sighting ports on the sides of the turrets.  This is consistent with British practice where their post-Jutland designs did away with hoods in favor of ports. The close relationship between the British and Japanese navies meant that the Japanese designers were well aware of this changeover and incorporated this knowledge into improving their own designs.

2) The design of this mounting was very similar to that for the British 15"/42 (38 cm) Mark I.  For example, like the British gun, the rammers were mounted on a continuation of the slide and could ram at any angle of elevation.  Difficulties with this method, probably similar to those found by the British, led to the rebuilt mountings having a fixed loading angle of +3 degrees.  The mountings were powered from a hydraulic ring main.  The training gear used a worm drive which was subject to wear problems.  A double longitudinal bulkhead separated the two guns and also the working chamber.  This consisted of two flashtight bulkheads spaced about 20 inches (50 cm) apart.  A flashtight door in this bulkhead was the only access between the two sides of the turret.  The working chamber where shells and charges were transferred from lower to upper hoists was similarly subdivided.  Shell rooms were above the magazines.  The post-war US survey of Japanese Seacoast Artillery states that the coastal artillery turrets could be theoretically loaded at any angle up to +15 degrees but actually the loading angle could not exceed +5 degrees.

3) The US Naval Technical Mission to Japan report O-47(N)-1 states that "Japanese major caliber turrets (14 and 16-inch) are all of old design and were copied from the British-built turrets for the BB Kongo.  In general arrangement and in most details, they are similar to the British 15-inch turrets, but some improvements have been made by the Japanese . . .[including] Better flash tightness in gunhouses and working chambers.  All battleships were fitted with longitudinal flashtight bulkheads between the guns, and between the gun loading hoists in the working chambers. . . In the 16-inch turrets, the gunloading cages are designed to hold four one-quarter charges end to end, thus enabling a full charge to be rammed with a single stroke of the rammer."

4) Run out was by compressed air.  Gun elevation was by cylinder and piston attached to the rear of the slide.  Each gun loaded from a cage which contained the shell and all four charges laid end to end in a flash tight compartment.  This allowed the charges to be rammed in a single stroke.

5) The gun axes were 96 in (244 cm) apart.

6) The coast defense mountings are thought to be those originally intended for either Kaga or Tosa.  These turrets were more rectangular in appearance and were powered by individual oil hydraulic units rather than by a ring main as in the earlier turrets.  A post-war USN report states that the Tsushima battery lacked adequate fire control and communications equipment.

7) Armor thickness of original turrets given in "Nagato Details" by Sander Kindsepp:
    Face:  11.7 in (29.9 cm)
    Sides:  8.8 in (22.4 cm)
    Rear:  7.4 in (18.7 cm)
    Roof:  4.9 - 5.9 in (12.5 - 14.9 cm)
    Floor:  3.9 in (10.0 cm)

Armor thickness of modernized turrets given in "Naval Weapons of World War Two" by John Campbell:
    Face:  18.1 in (46.0 cm)
    Sides:  11.0 in (28.0 cm)
    Rear:  7.5 in (19.0 cm)
    Roof:  9.8 - 9.0 in (25.0 - 23.0 cm)

Coastal Defense Turrets given in "Survey of Japanese Seacoast Artillery, 1946" by US Army:
    Face:  12.0 in (30.5 cm)
    Sides:  12.0 in (30.5 cm)
    Roof:  4.0 in (10.2 cm)

Modernized turrets were given thicker armor plating during the 1930s rebuilds.

Data from
"Naval Weapons of World War Two" by John Campbell
"Battleships:  Axis and Neutral Battleships in World War II" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
"The Japanese Ships of the Pacific War" by The Koku-Fan
"Japanese Cruisers of the Pacific War" by Eric Lacroix and Linton Wells II
US Naval Technical Mission to Japan report O-19:  Japanese Projectiles General Types
US Naval Technical Mission to Japan report O-47(N)-1:  Japanese Naval Guns and Mounts-Article 1, Mounts Under 18"
US Naval Technical Mission to Japan report O-55(N):  "Defenses of Tsushima and Entrance to Sea of Japan"
US Army Report "Survey of Japanese Seacoast Artillery, 1946"
"Nagato Details" an unpublished paper by Sander Kindsepp
Special help from Rob Lundgren
Page History

19 April 2007 - Benchmark
11 May 2009 - Fixed typographical error
30 June 2012 - Added information about surviving guns, turret designs, armor thickness, use as coastal artillery and flashtightness of turrets