These guns and mountings were Armstrong designs and were similar to British designs of the early 1900s such as the 12"/45 (30.5 cm) Mark X with small changes. The pre-dreadnoughts Kashima and Katori, both built at Elswick, used guns built by Armstrong. Later pre-dreadnoughts were built in Japan and were armed with both Armstrong and Japanese-built guns. 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 Mikasa 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.

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)
Official Designation: 45 caliber 41st Year Type 30 cm Gun
Ship Class Used On 1 Katori, Tsukuba, Satsuma and Kurama Classes
Satsuma and Kawachi Classes
Mikasa as rebuilt 2
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 3 N/A
Rate Of Fire about 2 rounds per minute 4
  • ^During repairs after being captured by the Japanese, ex-Retvizan now Hizen, ex-Peresvet now Sagami, ex-Orel now Iwami and ex-Pobieda now Suo were rearmed with Japanese 12"/45 (30.5 cm) Armstrong guns. The secondaries on all ships were replaced with 6"/45 (15.2 cm) and 3"/40 (7.62 cm) Armstrong guns.
  • ^Mikasa sank at anchor the night of 11/12 November 1905 following ammunition and torpedo explosions. She was raised during the summer of 1906. An inspection determined that her guns had been ruined by their long immersion in salt water and needed to be replaced. 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.
  • ^Some of these guns had smaller chambers and powder charges, but apparently retained the same muzzle velocity and range tables.
  • ^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 1a 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)
  • ^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).


Range of Naval APC projectiles
Elevation Range
20 degrees 23,100 yards (21,120 m)
Range of Coastal Artillery APC projectiles
Elevation 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
  • These mountings generally resembled the British BVII(S) mounting used for the 12"/40 (30.5 cm) guns on the King Edward class.

Additional Pictures

Other Resources

Images at The Vickers Photographic Archive

See photographs 4415, 4416, 4618 and 4923 .


"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
"Warships of the Imperial Japanese Navy, 1869-1945" by Hansgeorg Jentschura, Dieter Jung and Peter Mickel
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
02 November 2016 - Converted to HTML 5 format
13 August 2019 - Added IWM photograph of Ikoma, reorganized notes
05 February 2022 - Added note about Japanese rearmament of captured Russian ships
28 May 2022 - Corrected typographical error and noted replicas on Mikasa