IJN "Number 13" Class Fast Battleship

[Triton]

Drawing of the Imperial Japanese Navy "Number 13"-class fast battleship. Although never officially named, the class is sometimes referred to as the Mikasa-class fast battleship. They are often classed as battlecruisers, but they were a larger, better protected and more powerful version of the Kii-class fast battleship. Four members of this class were planned, but construction was cancelled under the Washington Naval Treaty on November 19, 1923.

General Characteristics

Displacement: 47,500 tons normal
Length: 900 feet
Beam: 101 feet
Draft: 32 feet
Propulsion: Steam turbines, 22 boilers, 4 shafts, 150,00 hp, 30 knots
Crew: Unknown
Armament: 4 dual 18/45, 16 single 5.5/50 8 single 4.7/45, 8 24 inch TT (aw)

Ship List

Number 13 Would have been built at Yokosuka Navy.
Number 14 Would have been built at Kure Navy.
Number 15 Would have been built at Mitsubishi.
Number 16 Would have been built at Kawasaki.

Source:
The Ships That Never Were, a Collection of Cancelled Naval Projects 1918-1922 by Peter A Marshall

"World Battleships List: Japanese Dreadnoughts" at HazeGray
http://www.hazegray.org/navhist/battleships/ijn_dr.htm

 

[Flying Sorcerer]

Do you have a source for "The Ships that never were"? I haven't been able to locate it on Amazon. It sure sounds interesting.

 

[Triton]

Do you have a source for "The Ships that never were"? I haven't been able to locate it on Amazon. It sure sounds interesting.

I have been looking for the book as well without success. The drawings came from scans of Warships International No. 1, 1999 which cite The Ships That Never Were, a Collection of Cancelled Naval Projects 1918-1922 by Peter A Marshall as the original source.

 

[prolific1]

You know I could make a pretty cool painting of those two images if I had a high res copy of them and some reference as to the details needed.

 

[Tzoli]

I've updating my drawings of this class and in the near future (In a few weeks) I will post them here with more accurate and up to date data as you usually find on the net (For exampel their armament was (for the 46cm armed versions) 46cm/50 cannons (not /45 ones), 14cm/50 Guns and only 4x 12cm/45 AA guns)

 

[Colonial-Marine]

I'm a bit doubtful that this ship would have ended up at "only" 47,500 tons standard loading, especially if it was planned to use 50 caliber length guns.

 

[Grey Havoc]

An extensive integral armor scheme might possibly explain some of the planned weight savings.

 

[Tzoli]

only 305mm armour belt with 15 degrees inclination but you will see.
47.500 was not a valid displacement the smallest, Design A with 5x2 41cm (basically up armoured Kii) weighted 47.600tons
The 4x2 46cm/50 version, Design K weighted 49.000tons

 

[Tzoli]

The most accurate data comes from these official sources in the Hiraga archive:

Tables:

平賀譲デジタルアーカイブ · 二連、及三連41C/M砲塔搭載艦重量比較大体 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

平賀譲デジタルアーカイブ · 二連装、三連装及四連装41C/M砲塔搭載艦重量比較大体 大正八年十月二十七日 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

平賀譲デジタルアーカイブ · 二連装、三連装及四連装41cm砲塔搭載艦排水量比較大体 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

Alternative layouts for C and D:

https://iiif.dl.itc.u-tokyo.ac.jp/r...17#?c=0&m=0&s=0&cv=0&xywh=1889,1082,3656,1650

The two official drawings which seems to survived the past century:
Design D:

平賀譲デジタルアーカイブ · BATTLE SHIP "D" · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

Design H:

平賀譲デジタルアーカイブ · BATTLE SHIP "H" · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

 

[Grey Havoc]

We really need a thumbs up emote or similar.

 

[Tzoli]

Here is Design A of the No.13 preliminary series, It is basically an up-armoured Kii with 305mm belt of 15 degrees inclination rather 292mm of 12 degrees. Speed is basically the same but the extra armour and the engine to propell it meant an extra 5.000tons of displacement.

IJN No.13 Class Preliminary Design A by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 262,13 (wl) x 32,4 meters
Displacement: 47.600tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 152.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Design B was the first step towards something different something new, Triple turrets but placed in Kongo style layout being turbine rooms separated by the 3rd turret.

IJN No.13 Class Preliminary Design B by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 265,17 (wl) x 32,4 meters
Displacement: 48.200tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 153.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
4x3 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Next is Design C with 3x2,2x3 41cm turrets but in the Hiraga there were two layout variants: 2-3-3-2-2 and 3-2-2-2-3:

IJN No.13 Class Preliminary Design C by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design C Alternative by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 268,22 (wl) x 32,4 meters
Displacement: 50.000tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 156.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
2x3,3x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[airman]

Which names of these ships were proposed ? Any suggestions ?

 

[Tzoli]

No that is why they are called Number 13 class as the last 4 of the 8-8 fleet after the two Nagatos, two Tosa/Kagas, four Kiis and four Amagis.
But my idea for them based on if they were considered as Battleship (Province names):
IJN Tajima IJN Bingo IJN Hitachi IJN Chikugo

or as battlecruisers (large mountain names):
IJN Norikura IJN Ena IJN Hotaka IJN Azuma

 

[airman]

No that is why they are called Number 13 class as the last 4 of the 8-8 fleet after the two Nagatos, two Tosa/Kagas, four Kiis and four Amagis.
But my idea for them based on if they were considered as Battleship (Province names):
IJN Tajima IJN Bingo IJN Hitachi IJN Chikugo

or as battlecruisers (large mountain names):
IJN Norikura IJN Ena IJN Hotaka IJN Azuma

Nice suggestion , i have seen the reference and probably could had been names like first suggestions : they were super-battleships based on Tosa .

 

[Tzoli]

Not precisely. Kaga/Tosa was started as an improved Nagato in 1918/19 a modified Tosa was designed with base characteristics of the Kii, Amagi too based on Kaga and BC version of Nagato, then No.13 was begun as an improved Kii.
And Nagsto likely was based on a Vickers export design for Japan (4x2 16")

 

[Tzoli]

Like Design C, Design D too had two variants, the alternative showing a different placement of the 3rd and 4th version. Otherwise this proposal was similar to the Fuso and Ise classes some 10 years prior.

IJN No.13 Class Preliminary Design D by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design D Alternative by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 271,27 (wl) x 32,4 meters
Displacement: 52.700tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 160.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
6x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Dorknought]

The BC were named for temples as apposed to just big mountains.

Top of the list for BC would be:
Aoba, Kinugasa, Myōkō, Nachi, Ashigara, Haguro, Chōkai or Maya. Furutaka and Kako were rivers as per cruiser naming conventions.

These ships would nominally be replacement for the turn of the century 1st generation Armoured Cruisers so these could be reused:
Asama, Tokiwa, Yakumo, Azuma, Izumo, Iwate

Under the law No13 were BC so the above are more likely but if Battleships, they tended to be coastal provinces:

Standout ones are Yamato, Musashi and Shinano (Owari, Kii, Suruga and Omi were the Kii Class (No.9, 10, 11 and 12) but as an 8-8 replacement and convincing the population that these ships are ncesessary upgrades then names from the pre-dreadnoughts would be likely: Iwami, Hizen, Sagami, Suwo, Tango, Asahi, Shikishima, Fuji.

The Japanese never reused names from ships that were lost so Yashima, Hatsuse and Kawachi will be off the lists.

 

[Tzoli]

Furutaka and Kako were started as light cruisers so river names are appropiate.

And no, the Battlecruiser namesakes were Mountains as evident with the Kongo and Amagi classes and listed in every sources.
Also your logic of coastal provinces do not stand as 95+% of Japan's provinces are coastal so statistically it is very likely a new battleship gets a coastal province name.
Yet Japan had IJN Yamashiro, IJN Shinano, IJN Kawachi, IJN Yamato (I know it is the old name of Japan but still an inland province)

As for re-using names, the IJN did not built enough capital ships to gotten with the issue of re using older names.

 

[Dorknought]

Yamamoto Naming Proposal

On April 23, 1895, the then Minister of the Navy, Yamamoto Gonbei, wrote and sent to the Emperor a proposed system for naming IJN ships.

In general, names of battleships and first class cruisers shall be selected from names of provinces within the Empire or from names of shrines traditionally dedicated to the protection of the nation.
Names of other warships shall be selected from names of country and provinces within the Empire.
In addition, names can be selected as appropriate in accordance with previous practice, such as the names Shikishima, Asahi, Akitsushima, Yashima, and Fuso, without regard to ship type.

After some refinements, involving such details such as how long after a ship is stricken is its name usable for a new ship, the guidelines that would basically remain intact until the demise of the IJN were established.

History and Technology - Naming of Warships in the Imperial Japanese Navy - NavWeaps

www.navweaps.com

Significance in Japanese religion
Folk religion has continued throughout the ages to be a very major force in the life of the Japanese people, particularly the aspect of the association between religious beliefs and practices with sacred mountains. This practice of mountain worship holds a significant place in Japanese beliefs and had become widespread throughout Japan’s history. It has been observed that nearly every high mountain top has had its own dedicated shrine at one point, with some receiving pilgrimages every year from thousands of worshippers. This collection of diverse phenomena linking religious activities and beliefs with sacred mountains is referred to as sangaku shinkō.

Three Mountains of Dewa - Wikipedia

en.wikipedia.org

 

[Tzoli]

This still not apply as Battlecruisers and heavy cruisers were named after mountains not shrines, light cruisers after rivers and so on:
I know Japanese people has deep connection to mountains and other natural things.

The system used through the end of World War 2 is as follows.

Ship Type	Source(s) of Names
Battleships	Country/province names
Battlecruisers	Mountain names
First class cruisers	Mountain names
Second class cruisers	River names
Coast defense ships	Old names retained (no new construction)
First class destroyers	Meteorological phenomena
Second class destroyers	Plant names
Torpedo boats	Bird names
Submarines	Numbers

From the Japanese Wiki of the Kongo class:
命名の由来
この頃の日本艦船の命名慣例によれば戦艦には旧国名が名付けられているが、本級はまず装甲巡洋艦（一等巡洋艦）として計画されたことから、同型艦全て山岳名が名付けられている。

Origin of the name
According to the naming convention of Japanese ships around this time, the old country name was given to the battleship, but since this class was first planned as an armored cruiser (first-class cruiser), all ships of the same type are named mountain names.

And the goes for each ship.
Yes mountains with more spritualistic value or history preferred over others but the ships still not named after Shrines. Every source agrees on mountains even Japanese ones.

 

[Tzoli]

Next is the E design introducing the quadruple turret into the IJN:

IJN No.13 Class Preliminary Design E by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 262,13 (wl) x 32,4 meters
Displacement: 46.600tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 150.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
3x4 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Continue with Version F where the forward quadruple turret got replaced by two twins increasing the survivability of the forward armaments:

IJN No.13 Class Preliminary Design F by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 268,22 (wl) x 32,4 meters
Displacement: 48.400tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 154.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
2x4,2x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Design G is a different approach with the aftermost turret got replaced by two twins but also a firepower increase was in order by a twin turret forward to 14 barrels:

IJN No.13 Class Preliminary Design G by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 262,13 (wl) x 32,4 meters
Displacement: 52.800tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 162.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
2x4,3x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Next is Design H another 14 gunned variant but in only 4 turrets: 3 quadruple and one twin, basically an added twin version of E:

IJN No.13 Class Preliminary Design H by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 269,75 (wl) x 32,4 meters
Displacement: 50.600tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: 158.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
3x4,1x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

And now the last of the 41cm armed versions and the ultimate such armed designs the I and J with 4 quadruple turrets!

IJN No.13 Class Preliminary Design I/J by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 274,32 (wl) x 32,4 meters
Displacement: 54.000tons (standard) on J 50.000tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes, On J 279mm Belt and 102mm Deck
Engines: 165.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
4x4 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

And finally the 46cm armed versions begun with Design K. The official hiraga archive sketches shows that the Breyer stlye drawing of this class showing Nagato style arrangement and single funnels was wrong, but when Breyer collected his data he might not had access to the complete archive.
I've also made a slightly modified version with Y shaped funnel and impred AA guns (4x2 rather 4x1 12cm and added an extra pair of twin 40mm Vickers AA guns)

IJN No.13 Class Preliminary Design K by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design K V2 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: unknown, I've chosen 271,27 (wl) x 32,4 meters
Displacement: 49.000tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: Unknown, probably 158.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
4x2 460mm/50 Type 5 / 5th Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Grey Havoc]

Great job!

 

[ngv]

fantastic work as always. To go off topic how long does one of these take to draw up?

 

[Tzoli]

From nothing many hours/days, but if I only had to modifey an existing drawing only a few hours

 

[Tzoli]

Design L is the next step mounting 10 46cm cannons in 5 twin turrets:

IJN No.13 Class Preliminary Design L by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design L V2 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: unknown, I've chosen 277 (wl) x 32,4 meters
Displacement: 56.900tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: Unknown, probably 165-170.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
5x2 460mm/50 Type 5 / 5th Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Next is the 12 gunned 46cm version, Design M:

IJN No.13 Class Preliminary Design M by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design M V2 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: unknown, I've chosen 274,4 (wl) x 32,4 meters
Displacement: 57.200tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: Unknown, probably 165-170.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
4x3 460mm/50 Type 5 / 5th Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

And the last of the known No.13 preliminary designs, variant N which only a very small sketch about the number of turrets exists:

IJN No.13 Class Preliminary Design N by Tzoli on DeviantArt

www.deviantart.com

IJN No.13 Class Preliminary Design N V2 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: unknown, I've chosen 277,1 (wl) x 32,4 meters
Displacement: Unknown, probably 60.000tons (standard)
Armour: 305mm Belt inclined at 15 degrees, 114mm Deck, 76mm Slopes
Engines: Unknown, probably 170-175.000shp Gihon Steam Turbines, 4 shafts
Speed: 56km/h (30knots)
Armaments:
3x3,2x2 460mm/50 Type 5 / 5th Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 120mm/45 Type 10 / 10th Year Type AA Guns,
8x1 61cm Above Water Torpedo Tubes

 

[Tzoli]

Regarding these ABC designs as part of the Kii class or the No.13 class:
Part of translation from the book
世界の大艦巨砲　八八艦隊平賀デザインと列強の計画案
- The World's Largest Ship Cannon 88 Fleet Hiraga Design and Plans of Great Powers
ISBN 978-4-7698-2955-3

https://7net.omni7.jp/detail/1106673851

/Proposed Installation of Quadruple-Gun Turrets
The previous chapters have described the battleships and battlecruisers of the Eight-Eight Fleet. The purpose of them was to clarify the whole picture of the Eight-Eight Fleet Plan based on new facts from the Hiraga materials, and one of the results was a new ship type for the Amagi class battlecruiser, with a fused chimney silhouette. There is no doubt that Hiraga was responsible for all of this work, including the revision of the Nagato class and the numerous proposals for the Kaga class battleship and Amagi class battlecruiser, and the vast amount of his documents is the best evidence of this.
I mentioned this again because a very small number of people have objected that these basic plans are in the hands of different persons. Of course, even through the work was done by Hiraga, he did not do it all on his own. Naturally, his subordinate shipbuilding officers and engineers must have been ordered to do the work. However, as long as it incorporates Hiraga's design philosophy and intentions, it should be called a Hiraga design.
In March 1919, the Amagi class basic plan B64 was approved, as mentioned above, and of course the next step was to begin planning for a new battleship to follow the Kaga class.
As for the Eight-Eight Fleet Plan, four battleships and four battlecruisers remained in the plan. In October of the same year, Hiraga submitted his opinion on the proposal of the quadruple-gun turret "in relation to the last six-ship of the Eight-Eight Fleet". However, the latter part "in relation to the..." seems to be supplemented by the editor of the Hiraga manuscripts, and the original document is only the "quadruple-gun turret proposal". The Nagato, Kaga, and Amagi classes continued to adopt the use of a twin-gun turret for their main guns, but from around this time, discussions on the use of turret with three or more guns began to gain momentum.
One of the reasons for this was the question of whether Japan could continue to use twin-gun turret confronting the new American battleship, the South Dakota class, which is equipped with four triple-gun turrets of 16-inch 50-caliber guns.
Proposals and opinions on the next generation of battleships were made by both fleet and shipbuilding officers, and study meetings were held several times from March 1920 onward.
Therefore, there are many related documents from this period in the Hiraga materials. During this period, Hiraga himself seems to have gained knowledge of the opinions about the limit of technical possibilities from specialists of military engineers, and one of his conclusions must have been to submit his opinion on the proposal of the quadruple-gun turret. In Hiraga's opinion, the quadruple-gun turret should be adopted because of the advantages of the ship's design and gunnery capability, but there were not enough decisive factors to convince anyone.
In July 1920, the long-awaited budget for the completion of the Eight-Eight Fleet was approved, and all pending battleships and battlecruisers were ready for construction. Construction of Tosa, for which the budget had already been approved, began in February of the same year, and Kaga in July. Similarly, construction of the Akagi and amagi began in December.
In October, the Engineering Headquarters was again renamed the IJN Technical Headquarters. In December, Hiraga was officially appointed the chief of basic planning, and Kaizo Yamamoto was promoted to the head of the fourth department. And the basic plan for the next battleship Kii class was approved on September 4.
The basic plan for the Kii class was completed with minimal modifications to the Amagi class, and was approved as the proposal number B65, without going through several trials of proposals as before.
It is thought that, in order not to waste time without deciding the main gun and turret design for the next capital ship, only the first and second ships of the Kii class were built as the modified Amagi class for the time being, and the new main gun was to be applied to the third and later ships of the Kii class and the four battlecruisers No.8, 9, 10, 11.
However, the basic plan number B65 used here was used again for the Super Type-A Cruiser.

/Methods to Complete the Construction of the Fleet
A memorandum dated February 2, 1920, "Method to Complete the Construction of the Fleet by 1927", stated that the four battleships to be ordered from now on should be the same as the Kaga class and the four battlecruisers should be same as the Amagi class, and the battlecruiser started construction in 1920 should be replaced with battleship, and the materials (steel plates) for it should be ordered immediately from abroad. In other words, it was stated that about 10,000 tons of steel plates equivalent to one Kaga class ship should be ordered immediately.
This memorandum indicates that the naval authorities at that time felt a sense of urgency regarding the timing of the completion of the Eight-Eight Fleet.
Under these circumstances, the basic plan of the next battleship Kii classwas decided in September of the same year. Hiraga's thought was that the same type as Tosa was too ineffective, so he planned the Kii class as a modified version of the Amagi class.
As shown in the table on page 129, hull dimensions, engines, and armament are all the same. Only the armor plan was revised to increase the thickness of the waterline armor belt by 1.5 inches, and the barbette, fore defence bulkhead, conning tower, armor deck, and smoke route by about 1 inch.
This increased the displacement by 1600 tons, slightly increased the waterline length and length between perpendiculars due to the change in draft, and slightly changed the ship's breadth due to the increase in the side armor plates. Also, speed was reduced by 0.25 knots.
As a result of these revisions, it is concluded that the Kii class has the same armor and armament as the Kaga class, but has an advantage in speed.
The Kii class is generally interpreted today as four ships of the same type, but as mentioned above, the IJN Technical Headquarters intended to plan the third and later ships as a new type. On October 12, 1921, the construction order was issued for only two ships, the Kii at Kure Arsenal and the Owari at Yokosuka Arsenal. At this time, it was already one month before the Washington Naval Conference, and of course the construction of these two ships were destined to be cancelled before their keel laying.
In August 1921, Hiraag left behind a memorandum in which he stated the following regarding the extent of improvements that could be made to battleships and battlecruisers currently under construction or planned, based on the assumption that the Washington Naval Conference would impose limitations on future capital ships.
Kaga and Tosa cannot be revised because their construction is already underway, Amagi and Akagi can be revised if decided immediately, Takao and Atago can be revised since they are not yet under construction, and the Kii type can also be revised.
Specifically, for the Amagi class, the thickness of the waterline armor belt was increased by one inch, the armor deck was increased from 3.75-inch to 4-inch, and the turret canopy was increased from 5-inch to 6-inch. The weight increase due to these revisions is expected to be 634 tons, and the speed is estimated to decrease by 0.125 knots to 29.825 knots.
As for the bar berbette, it is stated that no revision was possible because the order had already been placed with England. The fact that barbette armor of the Amagi class was made in a foreign country is mentioned in the memorandum, which suggests that the amount of work could not have been handled by steelworks of the Kure arsenal. Was there any problem with confidentiality?
As for the Kii class, the armor belt was increased by half an inch to 12-inch, the rear waterline armor belt was increased by one inch to 10-inch, and the thickness of the main gun turret front shield was changed from 12-inch to 13-inch, resulting in an increase of 130 tons to 43,990 tons and a speed was calculated as 29.625 knots.
In the explanation of the Kii class to the Congress, the construction cost of one vessel was requested at 37,269,000 yen and the displacement was 41,000 tons (909 yen per ton). The actual construction cost was expected to be nearly double this amount.

/Turret Arrangement Differs from Foreign Ships
Now, the issue is the ship type after the third ship of the Kii class. As an appendix to Hiraga's opinion on the proposal of the quadruple-gun turret, the above-mentioned drawings A to M are attached, showing a turret arrangement.
Of these, A to H were variations with 10 to 16 41cm-guns mounted in twin-gun turret, triple-gun turret, quadruple-gun turret, or a mixture of these, and K to M were variations with 8 to 12 46cm-guns. The speed were all set at 30 knots.
All armament other than the main gun was the same as that of the Amagi class, and the thickness of the waterline armor belt was changed from 10 inches to 16 inches. The displacement was changed from 46,660 tons to 57,200 tons.
Of these, proposals D and H are shown separately in Figures 42 and 43, as more detailed figures are attached.
Proposal D is equipped with six twin-gun turrets and 52,700 tons displacement would require more than 150,000 shaft horsepower to achieve 30 knots speed at this size. Naturally, the weight related to main guns was largest among proposal A to H, reaching 11,154 tons (929.5 tons per gun).
The IJN experienced six-turret ships on the Fuso and Ise class, but the area covered by turret on the deck is large, and it is also disadvantageous in terms of powder magazine arrangement and blast protection. Even taking into consideration the advantages of a six-turret ship, such as high firing speed and low recoil per turret, the arrangement is not advantageous.
In contrast, proposal H has an arrangement with three quadruple-gun turrets and one twin-gun turret, making it a 14 41cm-guns ship. With a 56,000 tons displacement the weight related to the main gun was 10,294 tons, and the weight per one main gun was 735.3 tons, a decrease of 194 tons compared to the six-turret ship.
The effect of the quadruple-gun turret was significant, increasing the number of the main guns by two while reducing the displacement by 1,100 tons.
The arrangement of the twin-gun turret in the A-turret was a unique layout seen in Hiraga's design, which allowed for larger defensive distance on ship side by arranging a smaller-diameter turret in the bow, where the width of the hull was reduced. This layout was also used for the Kongo-replacement design in Showa period.
In contrast, shipbuilders in the U.S., England, Italy, and other countries have chosen a different perspective, that of ship stability, and have placed the multi gun turret in the A-turret position. Examples are the Nevada class, the Cavour class, and the King George V class. The only exception was the Austrian dreadnoughts, the Ersatz-Monarch class, which had twin-gun turret in the A-turret position and triple-gun turret in the B-turret.
However, we must not forget the fact that if the quadruple-gun turret is placed in the B-turret position, as in the H plan, the exposed barbed surfaces are large and the weight involved in the defense is high.
The quadruple turret in proposal H fixes two guns for each housing, which is different from the form of two twin-gun turrets joined together.
Since fire control can be carried out in each unit of two guns, it is said to be similar to the case of a twin-gun turret, and there should be few problems. However, the firing speed is inferior, and the simultaneous firing of four guns should be avoided because of the large impact on the hull structure.

/About the Last Battlecruiser of the Eight-Eight Fleet
The details of the Kii class is clear, as they are numbered and armor arrangements for them are drawn. However, how far had the plans of the last six ships of the Eight-Eight Fleet progressed?
The existence of these plans is not known even in the vast amount of Hiraga materials. In other words, there are no basic plans with official plan numbers for battleships after A127 and for battlecruisers after B65 in the Hiraga materials.
Hiraga's specific explanation of this is in his statement "On the New Ship Type", dated June 12, 1921.
The purpose of this statement was to advocate how the Yubari type light cruiser, which he had planned, had superior performance at a lower construction cost. In the last part of the statement, "On the last four battlecruisers of the Eight-Eight Fleet", he touched on this issue.
A summary of this is as follows.
"Considering the situation, these four ships are in the process of being fitted with 18-inch guns. No matter what obstacles there may be in the development of the 18-inch gun, it will eventually succeed, and we are eagerly awaiting a decision on the ship type.
This type is similar to the Kii class except that it is equipped with eight 45-caliber 18-inch guns,
1. Speed: 29 to 30 knots = target is 30 knots, but a decrease of up to 1 knot may occur due to economic considerations in hull design and should be left up to the designer.
2. Armor: Side armor belt must be able to withstand 16-inch shell at a distance of 12,000 meters on. Deck armor must be able to withstand 16-inch shell at a distance of 20,000 meters. Turret armor must be the same as side armor belt. Anti-torpedo protection must be able to withstand 200kg of explosives.
3. Cruising Range: 8,000 nautical miles at 14 knots
4. Capacity of mixed (oil and coal) fired boiler: Equivalent to the Kii class
Based on the above assumptions, we estimate that displacement will be abt. 49,000 tons, but for economic reasons, we would like to aim to keep it at abt. 47,500 tons."
The statement ends with an assertion of his theory that the four battlecruisers could be built at a lower cost by replacing the 5500-ton light cruisers that is scheduled to be built with the Yubari type.
In other words, at this point, Hiraga had not been ordered to draft basic plans for the last four ships (actually, it should be six ships).
Considering the fact that the basic plan was not ordered and the Washington Naval Conference was to be held after this point, it must be concluded that there was no concrete draft of the super Kii class basic plan.

/Is the Main Gun 18-inch or 16-inch?
In Hiraga's lecture given to the Crown Prince on December 18, 1924, he described the last four ships as follows.
"The remaining four ships of the Eight-Eight Fleet were still undecided, but they would be fast battleships with eight 18-inch guns, or at least twelve 16-inch guns with four triple gun turrets like American new battleships, and their displacement is to reach 48,000 tons. However, the Washington Naval Conference was held at the end of 1921 while this ship type was being developed."
It can be read from this that Hiraga's intention for the super Kii type was to be equipped with four twin 18-inch(46cm) gun turrets or four triple 16-inch(41cm) 50-caliber gun turrets.
The hull was designed to match the armament, and hull lines was decided to match the speed of 30 knots equipped with the necessary engine. It is notable that the armor plan was limited to protection against 16-inch guns, even when 46cm guns were installed.
One reason for this seems to be that the U.S. battleship under planned was designed to be equipped with 16-inch 50-caliber guns, so they decided the armor against 16-inch guns would be satisfactory.
However, the U.S. Navy was working on a prototype 18-inch gun at the time, and there was a possibility of switching the main gun of the new battleship to 18-inch if necessary, but this information was probably not available.
At the time, many study groups were held within the IJN to consider the main gun for the next capital ships. However, no definite conclusion was reached, and in the end, the choice was limited to either eight 46cm or twelve 41cm 50-caliber guns, both in four-turret ships, as Hiraga was aware.
Also at that time, the plan for larger diameter guns than 41cm in the IJN, 48cm 47-caliber gun under the secret name of "Type 5 36cm gun" was started around 1916. It was test-fired in December 1920, but the ninth shot caused damage to the barrel.
Thereafter, the gun housing part and ammunition loader were completed by 1923, but the project was discontinued. This experience suggests weapon engineers must have had some confidence in the practical application of the 46 gun, and it is assumed that Hiraga wished that too.
It is thought that Hiraga was waiting for the order to start the basic plan of the super Kii class for about one year from September 1920 the decision of the proposal of the Kii class to October of the following year the order for the construction of the Kii class. It is not so unnatural to think that he had some conception about super kii class in his mind during that period.

 

[donnyjie]

my refs:

https://www.secretprojects.co.uk/threads/japanese-dream-project-battleships-and-never-built-battleships.29390/post-614214

It seems that Ishibashi takes all the last 6 ships of the 8-8 fleet as the "Super Kii-class", and Hiraga just focuses on the "Last 4 Battlecruisers". I think most of the content of Ishibashi's and mine does not have conflicts except for small issues about categorizations or something. Ishibashi is an authority in the field of IJN's warships.

About the differences:

The "Main Gun Research Conference" did prefer the 4xIII config to 3xIV for No.11 (or Super-Kii), for the quad-turret was hard to build. Hiraga liked the quad ones because of the advantage in fire control, but he had to bow to reality.


The lecture to the crown prince on 1924.12.18 may be this one:

平賀譲デジタルアーカイブ · 大正十三年十二月十八日 極秘 列強軍艦設計ノ大勢ニ就テ 海軍造船少将 平賀 譲 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

The content that Ishibashi said was on pp.33 of the online doc. I try to translate it.

The Remaining 4 Ships of the 8-8 Fleet
Although the remaining 4 ships of the 8-8 fleet are totally undetermined, they might be fast battleships having eight 18-inch guns, or at least like the US battleships, having four 16-inch triple gun mounts (12 in total), with a displacement of 48000 tons. We persisted to this goal according to the international situation, and in the end of the 10th year we kept studying this new type of ship, the Washington Treaty came. When checking back the studies above, it's found that the Nagatos and Tosas, bttleships slow in speed, and the Amagis, battlecruisers weak in armor, came closer to each other. The Kiis in fact have better defense and the same speed as the Amagis, which are indeed the fast battleships. The two types of warship eventually mixed in one.

Hiraga mentioned 3 obscure designs in it, but probably they were "Treaty" ones (Kongo Replacement) of 35000t displacement, according to the context. (①&② on pp.92, ③ on pp.94 of the online doc).

①&②:
Main Guns: ①2xIV+1xII 16", ②2xIII+2xII 16"
Armor: Resist 16" shell at a distance of 15000m<d<25000m, Underwater protections
Speed: 25kt

③:
Main Guns: 3xIV 16"
Speed: 25kt

And Hiraga also mentioned gun configs in a draft of this lecture, 4xIII 16", 3xIV 16", and 4xII 18" in the last 4 or 6 ships (Even Hiraga himself was not sure of the exact number?).

平賀譲デジタルアーカイブ · 〔「軍艦設計」講演用草稿〕 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

 

[Pirate Pete]

In Warship 2017, in Warship Notes, Aiden Dodson addresses some of the ‘myths and zombies’ of warship designs.
He says this as regards the ‘13’ design is concerned:

 

[Tzoli]

In Warship 2017, in Warship Notes, Aiden Dodson addresses some of the ‘myths and zombies’ of warship designs.
He says this as regards the ‘13’ design is concerned:

I doubt Hiraga would had put that much effort in it if it was his own personal work. There are at least two detailed drawings exists about the ABC designs. There are indeed own designs in the archive but those are mostly data pages without much detailed work like the designs preceeding the Myoko class: C-41,42 and 43

平賀譲デジタルアーカイブ · 妙高 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

平賀譲デジタルアーカイブ · 〔C41・C42要目比較表〕/〔C43要目表〕/他4件 · 東京大学学術資産等アーカイブズ共用サーバ

iiif.dl.itc.u-tokyo.ac.jp

https://www.secretprojects.co.uk/threads/cruiser-projects-and-designs-of-the-ijn.39136/

 

[Tzoli]

These 4 are also likely part of the Kii design process:
Design X:

https://www.deviantart.com/tzoli/art/Kii-Class-Battleship-Preliminary-Design-X-875754361

Design Y:

https://www.deviantart.com/tzoli/art/Kii-Class-Battleship-Preliminary-Design-Y-875858116

Design Z:

https://www.deviantart.com/tzoli/art/Kii-Class-Battleship-Preliminary-Design-Z-875439728

Lenghtened Kaga/Tosa:

Modified Kaga Class Battleship Kii Preliminary by Tzoli on DeviantArt

www.deviantart.com

 

[Cjc]

When would have this class have been built? And when would the next class have been started (presumably with 20 inch guns)?