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
Pre-dreadnought Kawachi about 1918
Japanese 12" (30.5 cm) APC Projectile on
display at the Mikasa Museum in 1990
Display at Yamato Museum in Kure, Japan
Photograph copyrighted by Teimu Mig and used here by his kind permission
From left to right:
|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)|
|Twist||Uniform RH 1 in 28|
|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.
|Projectile Types and Weights
|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
|Propellant Charge||Large chamber: 250 lbs. (113.4 kg)
Small Chamber: 227 lbs. (103 kg) 80C2
|Muzzle Velocity||2,657 fps (810 mps)|
|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)|
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
|Train||About +150 / -150 degrees|
|Note: These mountings generally resembled the British BVII(S) mounting used for the 12"/40 (30.5 cm) guns on the King Edward class.|
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