12"/45 (30.5 cm) Armstrong
12"/45 (30.5 cm) 41st Year Type
30 cm/45 (12") 41st Year Type
Updated 02 December 2015

These guns and mountings were Armstrong designs and were essentially similar to British designs such as the 12"/45 (30.5 cm) Mark X with small changes.  The pre-dreadnoughts Kashima and Katori, both built at Elswick, used Armstrong guns, but the other pre-dreadnoughts armed with these weapons were built in Japan.  These were the first large-caliber weapons manufactured in Japan.

When the Japanese pre-dreadnoughts Satsuma and Aki were laid down in 1905, they were intended to be the first "all big-gun" battleships in the world, predating the famous HMS Dreadnought.  However, the cost of the Russo-Japanese War nearly ruined Japan, so these ships were completed with only four 12"/45 (30.5 cm) guns and the amidships guns were reduced in size to 10"/45 (25.4 cm) as a cost saving measure.

Similarly, the later Kawachi class had a mixed battery of these 12"/45 (30.5 cm) guns in four amidships turrets but 12"/50 (30.5 cm) guns in the end turrets.  This was because an improved financial situation allowed Japan to buy a limited number of higher-performance weapons.  The improved financial situation also allowed the Japanese to replace the 12"/40 (30.5 cm) guns on older ships with the more powerful 12"/45 (30.5 cm).

Most of the ships carrying these weapons were scrapped following the signing of the Washington Naval Limitation Treaty.  Turrets and guns from Katori, Ikoma and Kurama were then used as coastal artillery to defend Tokyo Bay.

Redesignated as 41st Year Type on 25 December 1908.  Redesignated in centimeters on 5 October 1917.


Bow turret on Mikasa in 1990
Mikasa is now a historical museum at Shirahama Beach in Yokosuka
Picture copyrighted by Troy Prince


Pre-dreadnought Ikoma
Bain News Service Photograph
Library of Congress Photograph ID LC-DIG-ggbain-19712
Click on this picture for a larger image


Pre-dreadnought Kawachi about 1918
The 12"/45 (30.5 cm) guns are in the beam turrets with 12"/50 (30.5 cm) guns in the end turrets
Bain News Service Photograph
Library of Congress Photograph ID LC-DIG-ggbain-19717
Click on this picture for a larger image


Japanese 12" (30.5 cm) APC Projectile on display at the Mikasa Museum in 1990
APC projectiles like these were not in use during the Russo/Japanese War
Picture copyrighted by Troy Prince

Display at Yamato Museum in Kure, Japan
Photograph copyrighted by Teimu Mig and used here by his kind permission

From left to right:

30 cm main gun shell
20.3 cm AP shell
20.3 cm AP shell powder canister
12.7 cm high angle gun shell
25 mm machine gun shell

Images at The Vickers Photographic Archive

See photographs 4415, 4416, 4618 and 4923

Gun Characteristics
Designation 12"/45 (30.5 cm) Armstrong
12"/45 (30.5 cm) 41st Year Type (Model 1908)
30 cm/45 (12") 41st Year Type (Model 1908)
Ship Class Used On
(see Note 2)
Katori, Tsukuba, Satsuma and Kurama Classes
Satsuma and Kawachi Classes (Wing Turrets, only)
Mikasa as modified
Date Of Design about 1904
Date In Service 1908
Gun Weight 60 tons (60.2 mt)
Gun Length oa N/A
Bore Length about 540.0 in (13.716 m)
Rifling Length N/A
Grooves (72) N/A
Lands N/A
Twist Uniform RH 1 in 28
Chamber Volume N/A
Rate Of Fire about 2 rounds per minute

1) Some of these guns had smaller chambers and powder charges, but apparently retained the same muzzle velocity and range tables.

2) Mikasa sank at anchor the night of 11/12 November 1905 following ammunition and torpedo explosions.  She was raised during the summer of 1906.  Following inspection, it was determined that her guns had been ruined by their long immersion in salt water.  Mikasa was repaired over the next two years and her 12"/40 (30.5 cm) guns were replaced with the more powerful 12"/45 (30.5 cm).  She was recommissioned in August 1908.

3) The post-war US survey of Japanese Seacoast Artillery states that these guns fired 2 rounds per gun per minute.

Type Bag
Projectile Types and Weights
(see Note)
APC - 850 lbs. (386 kg)
HE - 850 lbs. (386 kg)
HC - 850 lbs. (386 kg)
Bursting Charge APC - about 42 lbs. (19 kg)
HE - about 85 lbs. (39 kg)
HC - N/A
Projectile Length N/A
Propellant Charge Large chamber:  250 lbs. (113.4 kg) 80C2
Small Chamber:  227 lbs. (103 kg) 80C2
Muzzle Velocity 2,657 fps (810 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition Stowage per Gun N/A (probably about 100 rounds)
Note:  The post-war US survey of Japanese Seacoast Artillery states that these guns fired 881.6 lbs. (400 kg) AP shells.  Whether this was the naval shell or a new Army projectile is not defined.  Muzzle velocity with a 250 lbs. (113.4 kg) charge was 2,650 fps (810 mps).
Elevation With 850 lbs. (386 kg) AP Shell
Range @ 20 degrees 23,100 yards (21,120 m)
Coastal Artillery With 881.6 lbs. (400 kg) AP Shell
Range @ 33 degrees 30,000 yards (27,430 m)
Mount / Turret Data
Designation Two-gun Mount
   Katori (2), Tsukuba (2), Kurama (2), Satsuma (4) and Kawachi (4)
Weight  about 200 tons (203 mt)
Elevation about -5 / +15 degrees

Coastal artillery:  0 / +33 degrees

Elevation Rate N/A
Train About +150 / -150 degrees
Train Rate N/A
Gun recoil N/A
Loading Angle N/A
Note:  These mountings generally resembled the British BVII(S) mounting used for the 12"/40 (30.5 cm) guns on the King Edward class.
Data from
"Battleships of the World:  1905-1970" by Siegfried Breyer
"Naval Weapons of World War Two" by John Campbell
"The Big Gun:  Battleship Main Armament 1860-1945" by Peter Hodges
US Army Report "Survey of Japanese Seacoast Artillery, 1946"
"Japan Saves the Mikasa;  Battleship Sunk at Sasebo Nearly a Year Ago at Last Refloated" article in The New York Times dated 8 August 1906
British Naval Heritage in Micronesia:  Tangible evidence of the armament trade from 1890 to 1937 by Dirk H.R. Spennemann
Iki fortress Kurosaki Fort

Page History

09 May 2008 - Benchmark
11 May 2009 - Replace poor side view photograph of Settsu with a better one of Kawachi, added photograph of Ikoma
30 June 2012 - Added gun details and information about use as coastal artillery
26 April 2014 - Adjusted link for Iki fortress to Wayback Archives
01 November 2015 - Added projectile photograph
02 December 2015 - Changed Vickers Photographic Archive links to point at Wayback Archive