The Development of the Nagato class Battleships

[Tzoli]

Part I: The British Ancestry
The design history of the Japanese Nagato class battleships, the world's first and fastest 16"/410mm armed battleships is long, and only partially documented. The sentence being the Nagato class not only the first indeginiously designed Japanese Battleship or the first Battleship entirely designed by Yuzuru Hiraga is not accurate. Before the first known Japanese design: A-102 which could be connected to the Nagato class in 1915/16 was born, the famous British ship building firm Vickers offered four proposals to the Imperial Japanese Navy in 1913 armed with 16" cannons: Designs 646,646A,647 and 647A. Designs 646 and 647 were 16"/40 while the "A" sub variants were 16"/44 armed proposals. Norman Friedman briefly mentions these offers with some info on dimensions and armament: 4 twin 16" turrets, 16x 6" secondary guns, 8 submerged torpedo tubes and other guns as on the Kongo eg 16x 3" guns. Other noteworthy feature the relative high speed of these proposals, outmatching any battleships of the time and reaching the same values as the first generation battlecruisers like the Invincible class.
It is very likely that these proposals heavily influenced the creation of the Nagato class battleships, both in size, speed and armament!

Vickers Design 646
Norman Friedman mentions and provides some data for this proposal in his book: The British Battleship 1906-1946. As a basis for the drawing I've chosen a modified and lengthened Queen Elizabeth class battleship with some alterations on the bridge and mainmasts as well as of course 16" armed turrets.

Vickers Export Design 646 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 184,4 (pp) x 28,65 x 8,7 meters
Displacement: 29.000tons (standard)
Armour: 305mm Belt
Engines: Unknown, likely 68.000shp
Speed: Unknown, likely 44-46km/h (24-25knots)
Armaments:
4x2 406mm/40 (16"/40) Vickers Mark A Cannons,
16x1 152mm/50 (6"/50) Vickers Mark S Guns,
16x1 76mm/40 (3"/40) Vickers Mark N Guns,
8x1 533mm Underwater Torpedo Tubes

Vickers Design 646A
Design 646A was a slight modification of the baseline design 646 using 406mm/44 cannons (16"/44) rather the shorter /40 calibre one. This difference in main weaponry together associated with a somewhat different turret carrying them resulted a net increase in displacement by 800tons to 29.800tons. For this design to not look like a longer barrelled Design 646 I've repositioned the mainmast, moving it just behind the 3rd turret as well as changing the main crane's facing and modelled the turrets after that used on HMS Hood: Mark II, previously I've used a somewhat enlarged turret of the Queen Elizabeth class eg the Mark I turrets and arranged the 3" Guns somewhat differently placing more on the main deck level.

Vickers Export Design 646A by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 184,4 (pp) x 28,65 x 8,7 meters
Displacement: 29.800tons (standard)
Armour: 305mm Belt
Engines: Unknown, likely 69.000shp
Speed: Unknown, likely 44-46km/h (24-25knots)
Armaments:
4x2 406mm/44 (16"/44) Vickers Mark A Cannons,
16x1 152mm/50 (6"/50) Vickers Mark S Guns,
16x1 76mm/40 (3"/40) Vickers Mark N Guns,
8x1 533mm Underwater Torpedo Tubes

Vickers Design 647
After the 646/646A designs that Vickers offered for Japan another pair was offered, this time with an added length of 4,5 meters likely to better achieve higher speeds and a net increase of 500tons, otherwise it has the same armament and armour as 646.

Vickers Export Design 647 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 188,98 (pp) x 28,65 x 8,7 meters
Displacement: 29.500tons (standard)
Armour: 305mm Belt
Engines: 68.5000shp
Speed: 48km/h (26knots)
Armaments:
4x2 406mm/40 (16"/40) Vickers Mark A Cannons,
16x1 152mm/50 (6"/50) Vickers Mark S Guns,
16x1 76mm/40 (3"/40) Vickers Mark N Guns,
8x1 533mm Underwater Torpedo Tubes

Vickers Design 647A
Like how the previously mentioned Design 646A was a slightly modified version of 646, the same applies to design 647A a modification of the baseline 647 variant
The changes are: longer calibre /44 cannons rather /40 ones, extra 1.250tons of displacement and 1.500shp more power to offset this extra tonnage.

Vickers Export Design 647A by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 188,98 (pp) x 28,65 x 8,7 meters
Displacement: 30.750tons (standard)
Armour: 305mm Belt
Engines: 70.0000shp
Speed: 48km/h (26knots)
Armaments:
4x2 406mm/44 (16"/44) Vickers Mark A Cannons,
16x1 152mm/50 (6"/50) Vickers Mark S Guns,
16x1 76mm/40 (3"/40) Vickers Mark N Guns,
8x1 533mm Underwater Torpedo Tubes

 

[Tzoli]

Part II: The Japanese Designs

The design history as I've said earlier of the Nagato class battleships of the Imperial Japanese Navy is quite difficult to research, mostly because of missing material and the language barrier. While the language barrier could be overcome by translators and naval enthusiasts willing to translate Japanese texts, the missing material is the other major obstacle. It is known that the design number of the battleship class preceding the Nagatos, the Ise class had A-92, while Nagato's design number was A-114, which means we have a missing set of 21 battleship designs not accepted for construction. Research in the Hiraga archive resulted in two design which had such numbers: A-110 and A-112 which both had drawings.

Design A-102
First mention of the design A-102 was from an online source which describes this as the first known Nagato preliminary and which was similar to the "British Design".
Knowing that Vickers offered designs to the IJN in 1913 the Ise class started construction in 1915 I've created this drawing showing elements of both:
152mm secondary guns and similar arrangement as well, the first deck level and the aft supersturcture reminiscent to that of the Queen Elizabeth Class, hull shape and tripod bridge structure following that of the Ise class and finally of course the armament of 4 twin 41cm turrets that of the Nagato class.

Battleship Design A-102 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: Unknown
Displacement: Unknown
Armour: Unknown, likely 305mm Belt 25mm Deck and 51-76mm Slopes
Engines: Unknown, likely 70-75.000shp
Speed: Unknown, likely 45-48km/h (24-26knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
16x1 152mm/50 43rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
8x1 533mm Underwater Torpedo Tubes

Design A-110
The first Nagato preliminary design which I've found drawings of (at first partial then a complete one) in the Yuzuru Hiraga archive was design A-110. This preliminary proposal seems to be the first one designed by Yuzuru Hiraga showing his characterisitic pagoda style mainmast albeit only 6 and closely placed legs without a central elevator shaft. Japanese sources describe the bridge structure as very similar that of the Ise type eg a large circular base with likely similar or round bridge on top of it. At least one pair of 76mm AA guns were placed on the aft superstructure at a rather high level and good firing arcs, though close to the blast area of the 3rd turret when firing extreme forward. The tripod aft mast style meant that the boat crane either located on both of it's legs, on either side of the funnels or as I've depicted, on the hexapod mast forward. The Armour layout shows that the design was still pre-Jutland as evident of the thin 28mm deck armour, almost full hull length belt and deck armour, lacking only at the extreme ends eg the nose and stern but includes the steering room.

Original Hiraga documents:

平賀譲デジタルアーカイブ · 軍艦長門防禦装置後部改正案 · 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 · 一般艤装 軍艦長門後部改正案 二枚ノ内其一 · 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 · 一般艤装 軍艦長門後部改正案 二枚ノ内其二 · 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 · 軍艦長門大体計画改正案 · 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

Battleship Design A-110 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 28,95 x 9,14m
Displacement: 32.500tons (standard)
Armour: 305mm Belt 28mm Deck and 70mm Slopes
Engines: 60.000shp, 4-shafts
Speed: 45km/h (24knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Yuzuru Hiraga's Pre-Designs
The next four designs associated with the Nagato class design history labelled as A,B,C and D and they show what possible changes are required after examining the After Action Reports of the Battle of Jutland 1916 May 31.
Pre-Design A
The first version, Design A the maximum speed was increased to 27knots over the A-110's 24knots but for the cost increase to remain minimal and to not design and entire new hull, engine power was boosted by 33% from 60.000shp to 80.000shp and the sloped armour thickness reduced somewhat from 70mm to 51mm over machinery spaces. The savings in armour weight allowed a minimal 250ton increase in displacement despite the larger engine power. This first attempt shows the importance of high speed in a battle both chasing down or escaping from the enemy.

Original Hiraga documents:
Armour scheme:

平賀譲デジタルアーカイブ · 軍艦長門改正案比較 A. 327500TONS 27KNOTS 80,000S.H..P C. 33,800TONS 26.8KNOTS 80,000S.H..P · 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

Data tables:

平賀譲デジタルアーカイブ · Nagato改正案 大正5.8.8 · 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

Nagato Preliminary Design A by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: Unknown
Displacement: 32.750tons (standard)
Armour: 305mm Belt, 28mm Deck and 51mm at Machinery, 70mm at Magazines Slopes
Engines: 80.000shp, 4-shafts
Speed: 50km/h (27knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Pre-Design B
While Pre-Design A increased maximum speed of the A-110 study with reducing sloped armour thickness and likely overall armoured area to gain tonnage for larger engines, Pre-Desing B increased main deck armour from 28mm to 70mm while the displacement remained the same compared to A-110. This was likely achieved by reducing the armoured area of the ship notably abandoning the classical fully armoured hull and implementing the USN style all or nothing or partial all or nothing armour scheme where only the vital or vital plus some extra lengths were armoured and the rest of the ship eg the ends (everything forward of the 1st and aft of the 4th turrets) were unarmoured. Note that these armour thickness values were very close to the final Nagato design as built: 70mm Deck and 76mm Slopes.

Original Hiraga documents:
Armour scheme:

平賀譲デジタルアーカイブ · B. 32,500TONS 25KNOTS 60,000S.H..P D. 33,300TONS 26.9KNOTS 80,000S.H..P · 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 · B, C.及D 案 FORWARD SECTION AFT SECTION · 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

Data tables:

平賀譲デジタルアーカイブ · Nagato改正案 大正5.8.8 · 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

Nagato Preliminary Design B by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: Unknown
Displacement: 32.500tons (standard)
Armour: 305mm Belt, 70mm Deck and 70mm Slopes
Engines: 60.000shp, 4-shafts
Speed: 46km/h (24knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Pre-Design C
Pre-Design Variant C uses both aspects of the previous two proposals: increased engine power for higher top speed (Pre-Design A) and increased deck armour thickness to 70mm (Pre-Design B) to create a post-Jutland fast battleship. Of course these changes over the base A-110 design resulted in a hopping 1.300tons of extra displacement and slightly more than 1.000tons over the "A" proposal. As you can see on the original drawing the armour belt and deck now not entirely covers the hull, and the ends have rather light armour protection, mostly against destroyer calibre and near misses to stabilise hull displacement growth. It is more then likely that this Pre-Design C variant was chosen for further developed as overall we got very close to the Nagato as finished though there were still some differences: Partial All-or-Nothing armour scheme, above water torpedo launchers separated by a casemate, small base for the hexapod pagoda mast, and single pole mainmast aft.

Original Hiraga documents:
Armour scheme:

平賀譲デジタルアーカイブ · B. 32,500TONS 25KNOTS 60,000S.H..P D. 33,300TONS 26.9KNOTS 80,000S.H..P · 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 · B, C.及D 案 FORWARD SECTION AFT SECTION · 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

Data tables:

平賀譲デジタルアーカイブ · Nagato改正案 大正5.8.8 · 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

Drawing:

平賀譲デジタルアーカイブ · 軍艦長門改正案(C) · 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

Nagato Preliminary Design C by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 28,95 x 9,14m
Displacement: 33.800tons (standard)
Armour: 305mm Belt, 70mm Deck and 70mm Slopes
Engines: 80.000shp, 4-shafts
Speed: 50km/h (26,8-27knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Pre-Design D
The last of the Pre-designs, variant D is a somewhat of a modified A proposal. The engine power of 80.000shp and thus the speed of 50km/ or 27knots was remained but main deck armour thickness is halfway between the 28mm of A-110 and Pre-Design A and the 70mm of Pre-Designs B and C being 51mm. This resulted in a slight reduction of displacement by 200tons over version C. This mere 200ton saving over the better protected variant C seems not worth the reduction in the defensive capabilities. None the less it shows a steady evolution of the Nagato class and how various proposals tried to solve the problems arised after the Battle of Jutland.

Original Hiraga documents:
Armour scheme:

平賀譲デジタルアーカイブ · B. 32,500TONS 25KNOTS 60,000S.H..P D. 33,300TONS 26.9KNOTS 80,000S.H..P · 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 · B, C.及D 案 FORWARD SECTION AFT SECTION · 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

Data tables:

平賀譲デジタルアーカイブ · Nagato改正案 大正5.8.8 · 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

Nagato Preliminary Design D by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 28,95 x 9,14m
Displacement: 33.300tons (standard)
Armour: 305mm Belt, 51mm Deck and 70mm Slopes
Engines: 80.000shp, 4-shafts
Speed: 50km/h (26,8-27knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Design A-112
The next step in the development leading to the Nagato class battleships was Design A-112, an improved and modified Pre-Design C.
The changes include:
- Complete all or nothing armour scheme, being the protected area only extends towards the ends of the 1st and 4 main turrets
- The saved armour weight went into thickening the slopes from 70mm to 76mm
- Adding a casemate deck behind the 2nd turret

These changes introduced on this design was remained for the rest of the development of the class. The Hiraga style close legged hexapod pagoda mast, the casemated deck which improves fighting capabilities as the the forwardmost casemates on design C would be very wet and the all or nothing armour scheme.

Original Hiraga documents:

平賀譲デジタルアーカイブ · 軍艦長門改正図 · 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

Nagato Preliminary Design A-112 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 28,95 x 9,14m
Displacement: 33.300tons (standard)
Armour: 305mm Belt, 51mm Deck and 76mm Slopes
Engines: 80.000shp, 4-shafts
Speed: 49km/h (26,5knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Design A-113
This is another drawing I've found in the Hiraga archive connected to the Nagato class development but no design number associated nor any other description apart from a hull stress diagram and side view. The hull sides eg the freeboard height is somewhat higher then on the previous versions indicationg more thought went into seaworthiness and to reduce water spray on the deck and it is actually very close to the final hull. The aft superstructure deck just behind the 3rd turret also shows a close resemblance to the final version. The aft turret were moved somewhat more forward reducing the armoured area, while there seems to be armour plates at the base of the forward funnel and the angle of the pagoda masts legs indicates higher platform height which might be the reason of saving weight by reducing the armour length.

Original Hiraga documents:

平賀譲デジタルアーカイブ · B.S."NAGATO" CURVES OF BENDING AND SHEARING STRESSES. · 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

Nagato Preliminary Design A-113 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 28,95 x 9,14m
Displacement: 33.300tons (standard)
Armour: 305mm Belt, 70mm Deck and 76mm Slopes
Engines: 80.000shp, 4-shafts
Speed: 49km/h (26,5knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

 

[Tzoli]

Part III: Final Design, Proposals, Refits and Modernizations

IJN Nagato As laid Down
IJN Nagato was laid down in 1917 August 28. with the original Hiraga hexapod pagoda mast bridge with closely placed legs.
While the previous proposal which I've labelled A-113, still had many common elements of the final Nagato, some changes still occured on the design:
The hexapod pagoda mast of shorter height as used on the Pre Designs retained, the casemate or 1st deck lengthened, and the aft superstructure elements around the tripod mast simplified.
Japanese sources describe that the heptapod (6 legs and one larger central shaft) pagoda mast was adopted later for the Nagato when it was still under construction hence the use of hexapod here.

IJN Nagato As laid Down by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 213,36 (wl) x 215,8 (oa) x 29 x 9,10m
Displacement: 33.300tons (standard), 38.500tons (full load)
Armour: 305mm Belt, 70mm Deck and 76mm Slopes
Engines: 80.000shp, 4-shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Hidetaro Kaneda's Type A Bridge
Shortly after the ship laid down, in October 1917, Captain Hidetaro Kaneda proposed a plan to modify the bridge superstructure of the ship. This new Bridge included 9 legs, one larger central shaft including an elevator an 8 smaller symmetrically placed legs around it in a widely spaced manner basically and enneapod or novempod pagoda mast. The wide spacing allowed stability for the large platforms he envisioned for this proposlas and which includes:
- AA Platform for 8x 76mm AA guns
- Secondary gun and searchlight platform though the drawing seems to show light calibre guns either short barrelled 76mm, 57 or 47mm guns
- Searchlight platform for 8 searchlights
- Main 10m Rangefinder platform
- Firing command platform
- Director command platform

Hiraga did not liked this kind of pagoda mast because he feared excessive vibrations at the Rangefinder level as well as the top weight issues from the larger number of guns at higher level. But the Admiralty liked the idea and somewhat later Kaneda proposed a different "B" type bridge with oval shaped conning tower and sloped heavy armour and removed AA gun platform.

Original Hiraga documents:

平賀譲デジタルアーカイブ · 〔櫓檣改正案検討資料〕 · 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

IJN Nagato Modified Bridge Variant 1 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 213,36 (wl) x 215,8 (oa) x 29 x 9,10m
Displacement: 33.300tons (standard), 38.500tons (full load)
Armour: 305mm Belt, 70mm Deck and 76mm Slopes
Engines: 80.000shp, 4-shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
8x1 76mm/40 3rd Year Type DP-AA Guns,
8x1 76mm/25 41st Year Type Guns or 57mm/40 or 47mm/50 Hotchkiss Guns.
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

Hidetaro Kaneda's Type B Bridge
The second modified bridge variant Captain Hidetaro Kaneda proposed in late 1917. This variant still used a 8 legged or octopod pagoda mast though there was a centreline shaft for elevator but that only went from the bridge or conning tower level upwards. The uniqueness of this bridge is the oval shaped conning tower with inclined armour plates for added protection. Yuzuru Hiraga again not really fond of this bridge either but the Admiralty liked the idea so Hiraga had to redesign it's own 6 legged closely placed pagoda mast to the final widely placed heptapod (6 legs and 1 central shaft) as the final bridge structure for Nagato.

Original Hiraga documents:

平賀譲デジタルアーカイブ · 〔櫓檣改正案検討資料〕 · 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

IJN Nagato Modified Bridge Variant 2 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 213,36 (wl) x 215,8 (oa) x 29 x 9,10m
Displacement: 33.300tons (standard), 38.500tons (full load)
Armour: 305mm Belt, 70mm Deck and 76mm Slopes
Engines: 80.000shp, 4-shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
20x1 140mm/50 3rd Year Type Guns,
4x1 76mm/40 3rd Year Type DP-AA Guns,
4x1 533mm Underwater and 4x1 Above Water Torpedo Tubes

IJN Nagato as Finished
The 25th of November, 1920 saw the commissioning of the world's then strongest, fastest and possibly tallest battleship entering commission into the Imperial Japanese Navy: The IJN Nagato.
The first battleship to be launched and commissioned with 41cm/45 main armament, 49km/h (26,5knots) maximum speed and both a tall pagoda mast with it's tallest point at 41m from the waterline and 58,5m tall aft mainmast again from the waterline!
The tall pagoda mast allowed the installation of a large 10m rangefinder at a very high (32 meters) height for excellent target acquisition and accurate firing solutions, while the even taller mainmast allowed long range radio communications. The armament remained at first place till the end of the decade when HMS Nelson commissioned in His Royal Majesty's Fleet but her speed in the battleship category not surpassed until 1939 by the French battleship Richelieu!!!

IJN Nagato as Finished by Tzoli on DeviantArt

www.deviantart.com

The 1933-36 Modernizations
While the Washington Naval Treaty forbid the construction of new capital ships except for the United Kingdom which lacked 16" armed battleships hence allowed the construction of the two Nelsons, Japan was expected to hold only Nagato at first and not finish Mutsu but due to diplomatic manoeuvring and requests, by the end of the 1920's Japan too held two 16" / 41cm armed battleships. The other two navies to command 16" armed vessels were of course the RN with Nelson and Rodney and the USN with Colorado, Maryland and West Virginia. Interestingly, sometimes these ships were called the great seven as these were the most powerful warships of their time.
The ratification of the Washington Naval Treaty allowed the signatory nations to take a break from expensive capital ship constructions and to look elsewhere to improve their fleets. This was about to change at the abortive 1927 First Geneva and later the signed 1930 First London Naval Treaty which at first allowed constructions of capital ships up to 35.000tons displacement and a maximum 16" armament but eventually the treaty extended the battleship construction "holiday" till 1936/37 which forbid construction of new capital ships but allowed the modernisation of existing ones.
This option was extensively used by most of the major powers navies:
The RN started modernising it's extensive fleet including the 5 Queen Elizabeth and 2 Nelson class battleships as well as the 2 Renown and 1 Admiral class Battlecruisers,
The Italian Navy it's 2 Conte di Cavour and 2 Andrea Doria class battleships,
The USN was absent from this modernisation fever,
The French Navy due to budgetary problems only partially modernized her 3 Courbet and 3 Bretagne class Battleships but instead started desigining and building the 2 Donkerque class Battlecruisers,
And finally the Imperial Japanese Navy's 2 Fuso, 2 Ise and 2 Nagato class battleships as well as 3 out of 4 of the Kongo class Battlecruisers.

Nagato started her modernisation in August, 1933 at the Kure Naval Arsenal and lasted till January 1936, while Mutsu entered her modernisation phase in September 1934 at the Yokosuka Naval Arsenal and lasted till September 1936. During this time both the stern and nose sections got lengthened with a total of 9,14meters, the Gihon Steam Turbines replaced by Kampon-Parsons produced ones and the 21 Boilers got reduced to just 10 but overall engine power increased from 80.000 to 82.000shp, the funnels too got replaced by a single larger one. Both the forward pagoda superstructure and the aft tripod mainmast heavily reconstructed with many added platforms, the AA armament too got strengthened by 4 twin 12,7cm Type 89 DP-AA guns and 10 twin 25mm Type 96 Machine Guns. In place of the aft trapezoid shaped superstructure deck, aircraft facilities and a folding catapult was installed with a capacity to carry 3 seaplanes. Protection wise too the ships got upgraded with 127mm extra deck plating one deck below the main 70mm one.

IJN Nagato as Modernized by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 221,07 (wl) x 224,94 (oa) x 34,6 x 9,50m
Displacement: 39.120tons (standard), 42.850tons (full load)
Armour: 305mm Belt, 127mm Deck and 76mm Slopes
Engines: 82.000shp, 4-shafts
Range: 15.800km at 30km/h (8.560nm at 16knots)
Speed: 50km/h (26,75knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
18x1 140mm/50 3rd Year Type Guns,
4x2 127mm/40 Type 89 DP-AA Guns,
10x2 25mm/60 Type 96 AA Guns
3x Seaplanes, 2x Kawanishi E7K Alf, 1x Nakajima E8N Dave
IJN Nagato as Modernized

Late War AA Refit
The worsening war situation and the ever increasing aerial threat from the USNAF and USAAF as well as war experience showed that warships of the IJN were very much deficient in protecting themselves from such threats. As such every warship in the fleet gradually received more and more AA mostly in the form of 25mm Machine guns but in some cases 12,7cm DP-AA guns as well to increase their effectiveness fighting enemy aircrafts. This was the case with the IJN Nagato as well, which got her AA refit in mid-late 1944 in the form of one twin 12,7cm Type 89 DP-AA guns on both sides, a large number of 25mm triple and single AA guns around the hull especially on the stern, on the 2nd and 3rd turret tops and on a specially created AA platform connecting the bridge and the funnel increasing their number to around 119 barrels. The ship also received radar sets of the usual types: Type 13s on the mainmast aft, Type 21 on top of the pagoda mast and Type 22s on the Main Rangefinder deck. These additions required removal of at least 6 casemated guns partly due to topweight and partly due to battle damage.
English language sources says that during this refit the funnel and aft tripod mast was cut in height to improve the firing arcs of the AA guns but Japanese sources says this was done later in early 1945 and not late 1944 hence my drawing shows they in their intact form.

IJN Nagato AA Refit 1944 by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 221,07 (wl) x 224,94 (oa) x 34,6 x 9,50m
Displacement: 39.120tons (standard, probably)
Armour: 305mm Belt, 127mm Deck and 76mm Slopes
Engines: 82.000shp, 4-shafts
Range: 15.800km at 30km/h (8.560nm at 16knots)
Speed: 46km/h (25knots)
Armaments:
4x2 410mm/45 3rd Year Type Cannons,
12x1 140mm/50 3rd Year Type Guns,
6x2 127mm/40 Type 89 DP-AA Guns,
25x3,10x2,24x1 25mm/60 Type 96 AA Guns
3x Seaplanes, Mitsubishi F1M Pete
Sensors:
Type 13 Air-Search Radars (2 sets)
Type 21 Air/Surface-Search Radars (1 set)
Type 22 Surface-Search Radars (2 sets)

The Proposed Aircraft Carrier Conversion
Between 1942 June 2nd and 7th a major naval battle happened in the middle of the pacific ocean near some uninteresting atoll called Midway, between the United States Navy and the Imperial Japanese Navy. During this battle the IJN lost many excellent and skilled pilots as well as 4 fleet carriers: Akagi, Kaga, Hiryu and Soryu. The catastrophic loss in this battle meant that the Imperial Japanese Navy got short of long range striking capital ships: Aircraft Carriers compared to the United States Navy. To remedy this aircraft carrier construction and development received high priority in the Navy but also to find other means to fill up the gap the 4 fleet carrier loss created. Among the emergency plans called the conversions of the heavy cruisers and battleships/battlecruisers still available to the navy into aircraft carriers. It was estimated by the Naval General Staff and the Naval Technical Department that the heavy cruiser conversions was required 9 months for an aircraft capacity of 30 planes and 18 months for the capital ships with a capacity to carry 54 planes and the following flight deck size:
The 4-4 Myoko and Takao class cruisers would had a 200 x 23,5m flight deck,
The 3 Mogami and 2 Tone class cruisers would had a 195 x 23,5m flight deck,
The 4 Kongo and 2 Nagato class capital ships would had a 220 x 34m flight deck,
and the 2-2 Fuso and Ise class battleships would had a 210 x 34m flight deck.

The Furutaka and Kako classes were considered too small for this role and hence not included while somewhat later the cruiser conversions were discarded as they were required for fleet service by the conclusion of the Naval Ministry. The Yamato class too was not included as they were too new too important and too powerful for such a conversion though the 3rd ship Shinano was decided for conversion, the Kongo class was later deemed to be require too much reconstruction work and their speed was still important as escorts for the carriers.
The Nagato class was discarded as their 41cm cannons were still quite powerful for surface action. That left the 2 Fusos and 2 Ises for conversion of which the the Ises taken priority due to battle damage. To speed up the conversion a modified plan was created which meant only a partial flight deck was to be installed first and full conversion would be taken at a later time so Ise was modified in Kure and Hyuga in Sasebo. Fuso and Yamashiro would be modified similarly after the two ships completed their reconstruction with the expected start of the work in 1943 June, Fuso in Kure and Yamashiro in Yokosuka.
As a side note this carrier crisis in the IJN lead of the conversion of the battleship Shinano, the heavy cruiser Ibuki into aircraft carriers and the construction order of the Unryu class simplified Hiryu type carriers.

Here I show you in my opinion the possible look of the Nagato class if were to be converted into a fleet carrier. I've originally chosen a Junyo type bridge but decided to modify the Shinano's bridge to fit on this hull. As for the aircraft storage, I could put 52 aircraft in her Hanger (40 + 4 spares of each type) though it would be quite crowded, but if Shinano type deck parking was taken into account the 54 aircraft capacity could be easily reached.

The 3 variants shows the 3 possible deck materials: Wooden deck, Full metal deck, Shinano type linoleum deck.

Nagato Class Carrier Conversion by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 201,17 (pp) x 221,07 (wl) x 224,94 (oa) x 34m (fd) 45,6m (max) x 9,50m
Displacement: Unknown
Armour: 305mm Belt, 127mm Deck and 76mm Slopes
Engines: 82.000shp, 4-shafts
Range: 15.800km at 30km/h (8.560nm at 16knots)
Speed: 50km/h (26,75knots)
Armaments:
6x2 127mm/40 Type 89 DP-AA Guns,
24x3,7x1 25mm/60 Type 96 AA Guns
Sensors:
Type 13 Air-Search Radars (2 sets)
Type 21 Air/Surface-Search Radars (2 sets)
Type 22 Surface-Search Radars (2 sets)
Single Hanger and na Aircraft capacity of 45-60 planes depending on storage (Hanger only or Hanger+Flight Deck)
22+4 Mitsubishi A6M Zero fighters
8+4 Nakajima B6N Jill Torpedo Bombers
10+4 Yokosuka D4Y Judy Dive Bombers



Sidenote: Maybe later in the future I will draw the 1924 curved funnel and 1931/32 pre modernization states as well.

 

[Antonio]

Impressive, brilliant!!, Thanks Tzoli.

 

[M. A. Rozon]

Agreed. Wonderful work. I love all of it!

 

[lordroel]

If you ever make a book about your designs Tzoli, i would buy it in a heartbeat.

 

[Coiler]

Great job with the design drawings!

I have a goofy "what if" design where the USN, instead of expending Nagato as a nuclear target, uses its large hull as an early missile "cruiser". All its IJN-era weapons, including the main guns, would get yanked off and replaced by four Mk.4 Terrier (the Boston-class vertical magazine one) systems and their necessary radars. It'd have a few light American guns for close-in work but that'd be it. (And a similar one for the Haruna if it survived the war)

Not exactly the most plausible or useful, but fun to think about.

 

[Dilandu]

I have a goofy "what if" design where the USN, instead of expending Nagato as a nuclear target, uses its large hull as an early missile "cruiser". All its IJN-era weapons, including the main guns, would get yanked off and replaced by four Mk.4 Terrier (the Boston-class vertical magazine one) systems and their necessary radars. It'd have a few light American guns for close-in work but that'd be it. (And a similar one for the Haruna if it survived the war)

Frankly, it's pretty hard to imagine why. Not only she was in pretty bad condition, but she also was completely non-standard (metric, by the way), and too slow for 1950s navy.

 

[Coiler]

Frankly, it's pretty hard to imagine why. Not only she was in pretty bad condition, but she also was completely non-standard (metric, by the way), and too slow for 1950s navy.

Oh, I'd never actually defend it as likely. It's just a very silly napkinwaffe concept of mine.

 

[Dilandu]

Oh, I'd never actually defend it as likely. It's just a very silly napkinwaffe concept of mine.

Ah. Sorry, I misunderstood you.

 

[lancer21]

Hi guys,

Seeing this recent Nagato topic, just wondering if there's any information regarding proposals to fully modernize their machinery and increase speed to as much as 29.3kts(!) according to japanese wiki. It appears these proposals were made before their modernization in the 1930s when the japanese choose just to uparmour them but not install new machinery like in all the other modernized BBs, hence the Nagatos speed dropping to 25kts.

There was a topic on j-aircraft some years back where a poster was discussing this subject, but for some reason the initial post has been deleted, so i can only go by memory. It appears that Kaga type machinery as modernized of 127,000HP (though according to Lacroix it's actually rated at 125,000HP, the slightly higher figure being perhaps the trial output- also it was peculiar in that it comprised two original but uprated turbines totaling 49,000HP and two new Mogami type ones totaling 76,000 HP) could have been installed giving a speed of about 29kts, though not clear if this applied for the fully uparmoured and bulged Nagato which was already at over 39,000 tons standard, or just for the basic Nagato (without bulging and additional armour) with the new machinery.

Any info as to the weight of Nagatos 82,000 HP machinery compared to Kaga's 127,000 HP as modernized? I swear i might have come across those figures in the past but i couldn't find it now if my life depends on it. I seem to recall Nagato's machinery may be something like 3100 tons while Kagas's more like 3700-3800 tons or so, but my memory may be completely off?

Thank you.

 

[Tzoli]

Nagato and Mutsu did received a complete overhaul engine wise as well, it's just the powerplant was not increased that much compared to the Fusos, Ises and Kongos for which I do not know the cause, maybe her hull form was much better and her base speed was quite higher compared to the Fusos and Ises even after the weight increase.
Nagato class as finished in 1920 had:
21x smaller Kampon boilers and 4x Gihon Steam Turbines for 80.000shp eg 3.800-4.000shp strong boilers
After the modernization in the late 1930's they had:
10x large Kampon Boilers and 4x Kampon-Parsons Steam Turbines for 82.000shp eg 8.200shp strong boilers
Note that the proposed modified Mutsu project of 1917 with 5 turrets on the same hull and engine power too would had 10 Kampon boilers. (8.000shp strong boilers)
While the Kaga/Tosa class for 91.000shp Curtis Steam Turbines, required only 12x Kampon boilers (7.500-8.000shp strong boilers)
Kaga after modernization and engine refurbishment rated 127.400shp for the same 12 boilers (10.600-10.700shp boilers)
Kii class for 131.200shp required 19x Kampon Boilers (6.900-7.000shp strong boilers)
Amagi class as built:
131.200shp from 4x Gihon Steam Turbines and 19x Kampon Boilers (6.900-7.000shp strong boilers) same as Kii.
Akagi after her modernization and refurbishments of engines rated as 133.000shp with the same 19 boilers. (7.000shp per boiler)
It is evident that shortly after 1916 the IJN acquired blueprints or know-how to construct larger more efficient and stronger boilers which are more space efficient as well.

Previous classes:
Kongo class as built:
Kongo, Hiei, Kirishima: 64.000shp from 4x Parsons Steam Turbines and 36x Yarrow boilers (1.700-1.800shp strong boilers)
Haruna: 64.000shp from 4x Brown-Curtis Steam Turbines and 36x Yarrow boilers
after the 1928-31 modernizations:
Kongo, Kirishima: 64.000shp from 4x Parsons Steam Turbines and 10x Kampon boilers (6.000-6.500shp strong boilers)
Haruna: 64.000shp from 4x Brown-Curtis Steam Turbines and 16x Kampon boilers (4.000shp strong boilers)
after the 1934-40 modernizations:
Kongo, Kirishima: 136.000shp from 4x Kampon Steam Turbines and 8x Kampon boilers (17.000shp strong boilers)
Haruna, Hiei: 136.000shp from 4x Kampon Steam Turbines and 11x Kampon boilers (12-12.500shp strong boilers)

Fuso class as built: 40.000shp from 4x Brown-Curtis Steam Turbines and 24x Miyabara boilers (1.600-1.700shp strong boilers)
Fuso's proposed 41cm reconstruction: 40.000shp from 4x Kampon Steam Turbines and 6x Kampon boilers (6.500-6.700shp strong boilers)
as modernized: 75.000shp from 4x Kampon Steam Turbines and 6x Kampon boilers (12.500shp strong boilers)

Ise class as built: 45.000shp from 4x Curtis Steam Turbines and 24x Kampon boilers (1.800-1.900shp strong boilers)
as modernized: 80.000shp from 4x Kampon Steam Turbines and 8x Kampon boilers (10.000shp strong boilers)

Now let's see the new built late 1930's early 1940's ships:
Mogami and Mikuma had 10x Kampon boilers for 152.000shp (15.000shp boilers)
while Suzuya Kumano, Tone, Chikuma, Ibuki, Ikoma had only 8x boilers for the same shps (19-20.000shp boilers)
Yamato class for 150.000shp required 12x Kampon Boilers (12.500shp boilers)
Soryu's 152.000shp and Hiryu's 153.000shp engines required 8 Kampon Boilers (19-20.000shp boilers)
Shokaku and Taiho class for 160.000shp required 8x Kampon Boilers (20.000shp boilers)

For weight of the Nagato class I will try to look for sources but in the Hiraga I think only the 1920's as finished weights were stored

 

[Tzoli]

Nagato machinery weight when completed was 4.100tons

平賀譲デジタルアーカイブ · 予算用Weight A115 116 117 118 B58 59 60 61 A119 120 121 122 · 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

But according to the IJN Battleship Bible (included page)
When finished machinery weight was 3.579tons for Nagato and 3.435tons for Mutsu and after modernisation 2.998 and 3.071tons respectively

 

[lancer21]

Hi Tzoli,

Thanks for the information, very interesting especially the tables. At least my memory wasn't that far off re machinery weights! If by any chance you would stumble upon Kaga's details that would be great.
I suspect that the reason they haven't put more powerful machinery in the Nagatos was because even with their reduced speed of 25kts they were as fast as the fully uprated Fuso and Ise so they could confortably operate together, and perhaps monetary concerns as well.
With the benefit of hindsight that was a mistake of course, any speed increase would have been good, but i wade into what-if territory now.
I am no good at anything to do with complicated maths, but still i was curious to find out for myself what would be the speed of the Nagatos as modernized and bulged but with 127,000HP (presumably the machinery would be heavier, so that would bring the standard displacement closer to 40,000 tons), so i wonder if there is a simple layman's way to calculate that?

Thanks again.

 

[Tzoli]

The relevant pages of the Kaga/Tosa class:

 

[Foo Fighter]

This is fascinating and ten times better than the idiot box. Keep it up please, the possibilities are pretty much out there but fascinating all the same.

 

[Tzoli]

Idiot box???

 

[Hardrada55]

Television...American slang, maybe British too.

 

[Foo Fighter]

Sorry, yes - television. In this instance British use, it takes very little thought to gain entertainment from the average program matter.

 

[cattalonX]

I have a goofy "what if" design where the USN, instead of expending Nagato as a nuclear target, uses its large hull as an early missile "cruiser". All its IJN-era weapons, including the main guns, would get yanked off and replaced by four Mk.4 Terrier (the Boston-class vertical magazine one) systems and their necessary radars. It'd have a few light American guns for close-in work but that'd be it. (And a similar one for the Haruna if it survived the war)

Frankly, it's pretty hard to imagine why. Not only she was in pretty bad condition, but she also was completely non-standard (metric, by the way), and too slow for 1950s navy.

What if the Russians get Nagato？？？

 

[Kingpin6100]

I have a goofy "what if" design where the USN, instead of expending Nagato as a nuclear target, uses its large hull as an early missile "cruiser". All its IJN-era weapons, including the main guns, would get yanked off and replaced by four Mk.4 Terrier (the Boston-class vertical magazine one) systems and their necessary radars. It'd have a few light American guns for close-in work but that'd be it. (And a similar one for the Haruna if it survived the war)

Frankly, it's pretty hard to imagine why. Not only she was in pretty bad condition, but she also was completely non-standard (metric, by the way), and too slow for 1950s navy.

What if the Russians get Nagato？？？

Likely a refit plan along the lines of Novorossiysk. Short term, lots of 25mm removed for single or twin 37s as space & power allow, 127/40s probably replaced by 100mm DP as the soviets had no 5" DP at the time. then a full refit plan mid 50s with the large caliber AA being replaced by 130mm SM-2-1s, and possibly 45mm quads if there is space.