Tzoli

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For some time I've already made these drawings just not yet posted here.
You can now see how the Tosa / Kaga class battleships evolved from an Improved Nagato to as laid down as a 5 turreted similar speed slightly larger battleship.

Let us begin:
Fast Nagato series:
A-115:

de6w1gy-8ef2abe7-e470-4594-9b93-a657e03b5019.png

Battleship Design A-115 was the first post Nagato (A-114) battleship design of the IJN. It contains some novel changes compared to her predecessor, including closely arranged funnels likely to reduce the possibility of spotting the ship's direction, armour wise a thinner but heavily, 25° inclined belt armour was introduced providing better protection at longer ranges then the vertical 305mm of the Nagato and which was consistent with the requirement of the Admiralty that all subsequent battleship type had to be stronger in one or more aspect then the previous one. But not only the armour was improved on this design but the speed too was increased considerably to 30knots or 56km/h over the already good speed of 26,5knots or 49km/h of the Nagatos. This of course required a longer sleek hull and bigger engines to achieve. The 25m extra length and half a meter wider beam allowed the install of almost 50% more (or in the case of the following design A-116 exactly 50% more) engine power into the hull to reach the desired speed. Despite the longer hull and more powerful engines the displacement was only risen by only 900tons showing how much weight can be saved by reducing the armour and incline it!

The design had the following characteristics:
Dimensions: 224,02 (pp) x 237,74 (wl) x 240,18 (oa) x 29,57 x 8,53 meters
Displacement: 34.700tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 113.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 56km/h (30knots)
Armaments:
4x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Data tables:

A-116:
de6roa6-1bc0d368-c447-4f78-b70b-a099835e52d8.png

Together with the previous Design A-115, A-116 was a fast 30knots / 56km/h Nagato type battleship, but while A-115 copied over the thin funnel protection of Nagato of only 1 inch or 25mm plates, A-116 provides a substantially thicker protection over this area of 6-9" or 152-229mm armour plates which resulted in a significant 2.000tons increase in displacement together with an extra 7.000ship engine power required to maintain the desired speed! The belt armour remains unchanged as introduced in A-115 having 229mm belt thickness which indeed looks thin for a late WW1 era battleship but if take into account that it was to be inclined at 25° to the vertical, this angled surface provides much better protection for long range gunnery fire.

The design had the following characteristics:
Dimensions: 224,02 (pp) x 237,74 (wl) x 240,18 (oa) x 29,57 x 9,14 meters
Displacement: 36.700tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 120.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 56km/h (30knots)
Armaments:
4x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official sketch drawing:

Funnel protection scheme:

Data tables:

A-117:
de6mrh4-9811e714-86f3-464c-9b91-45926d7366bf.png

Design A-117 was the faster version of the very first post Nagato battleship Design: A-115. While A-115 was designed for 30knots or 56km/h, A-117 destined for 32knots or 59km/h basically a faster Nagato a very true fast battleship combining fast battlecruiser type speed with good armour and excellent armament! The armour scheme copies that of A-115 together with the thin 1" funnel protection. But the extra two knots take at a cost: more then 13m more length, more then 30.000shp engine power and almost an extra 2.500tons of displacement.

The design had the following characteristics:
Dimensions: 237,74 (pp) x 253,9 (oa) x 29,57 x 8,76 meters
Displacement: 37.100tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 145.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 59km/h (32knots)
Armaments:
4x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Data tables:

A-118:
de6j5lr-c40dcd76-cc24-47b2-97a2-92119edb5a4c.png

Design A-118 was the last 4 turreted battleship design of the Imperial Japanese Navy and essentially a lengthened version of the previous A-117 with much stronger funnel base protection. While the designs A-115 and 116 was the Fast Nagato designs, together with A-117, A-118 too was an even faster Nagato type battleship with 32knots or 59km/h maximum speed and like how A-116 was companion design to A-115, A-118 too was a companion design to A-117. The difference being the even numbers had only 1" or 25mm armour plates around the funnel uptakes, the uneven proposals had a very thick 6 to 9" or 152-229mm platings! This resulted in an a base increase of probably around 1.000-1.250tons of armour alone and to maintain the desired high speed the hull was lengthened, the engine power increased by 5.0000shp to 150.000shp and displacement risen by 2.300tons over A-117.
None the less we got a nice sleek good looking very fast battleship which could catch even battlecruisers and fight equally with battleships!

The design had the following characteristics:
Dimensions: 243,84 (pp) x 260,00 (oa) x 29,57 x 9,14 meters
Displacement: 39.400tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 150.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 59km/h (32knots)
Armaments:
4x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official sketch drawing:

Data tables:

Start of the 5 turret proposals:
A-119:

de69z60-a27450af-984c-4d52-a465-8988e5ba82c4.png

A-119 was a unique design in the post Nagato series. The official drawing I've linked shows the 14 underwater torpedo tubes an extremely strong torpedo armament for a capital ship but as you can see the design number 119 looks like erased or ruled over. The next drawing A-120 depicts the same drawing with same dimensions just 1.000tons heavier and 4.000shp more engine power but without the underwater torpedo tubes. The A-120 drawing clearly shows the erased parts of A-119. Also the data tables in the Hiraga archive all states 4 above water 53cm torpedo tubes and different dimensions! So I've created two versions, this original A-119 which is exactly same above water as A-120 (minus the torpedo tubes) and the modified smaller version with above water torpedo tubes.

The design had the following characteristics:
Dimensions: 243,84 (pp) x 260 (oa) x 29,57 x 9,14 meters
Displacement: 39.400tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 120.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 56km/h (30knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
14x1 53cm Underwater Torpedo Tubes

Original drawing:

Data table:

Modified A-119 Design:
de6eyup-ea1f168e-58b2-49b0-8b10-3955ddc99755.png

As the data in the Hiraga Archive not entirely clear about this proposal (Having a drawing with different data then the data tables)
I've made both versions. While the drawing version shows 14 underwater torpedo tubes, this modified version was smaller (some 3 meters shorter) and displaced 1.000tons less, 38.400 rather 39.400 but the engine power and speed remained the same. It is possible that the 14 torpedo version was Yuzuru Hiraga's private own proposal or maybe a mis interpretation for a requirement set on one of the meetings of the Admiralty. As a side note the A-119 proposal seems to be the very first design to incorporate 5 twin turrets of the 41cm cannons introduced on the Nagato class and what essentially became the standard for all subsequent designs:
good speed, long sleek hull, 3 turrets aft 2 forward, 41cm main armament, 4 AA guns. until the later No.13 designs and their 46cm weaponry.

The design had the following characteristics:
Dimensions: 240,79 (pp) x 256,95 (oa) x 29,57 x 8,76 meters
Displacement: 38.400tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 120.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 56km/h (30knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Data table:

A-120:
de661tu-e87ba755-8064-4194-88b9-7f8d47264f57.png

Design A-120 was strongly connected to the previous A-119 proposal. This design probably the modified version of 14 torpedo launcher armed A-119 variant as the drawings show exactly the same hull and layout having only difference in the number and layout of torpedo tubes! Weirdly this design was heaver by 2.000tons despite only mounting 4 53cm torpedo tubes which could be the result of restoring the underwater torpedo bulkheads in the previously spaces allocated for the torpedo launchers

The design had the following characteristics:
Dimensions: 243,84 (pp) x 260 (oa) x 29,57 x 9,14 meters
Displacement: 40.400tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 124.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 56km/h (30knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Original drawing:

Data table:

Fast 5 turret versions:
A-121:
de402p4-797acfdc-4f69-492d-a1bd-ac938fb50f04.png

Design A-121 was most likely a modified fast version of A-119 with extra length and engine power added to reach the desired speed of 59km/h or 32knots. The next variant A-122 is very similar just longer by 14 meters. As I did not found any drawing for this particular proposal I've used a modified main armament layout of A-122 where I've changed the position and angle of the 3rd turret as well as the aft mast.

The design had the following characteristics:
Dimensions: 252,98 (pp) x 266,7 (wl) x 269,14 (oa) x 29,57 x 9,14 meters
Displacement: 40.600tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 150.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 59km/h (32knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Data table:

A-122:
de3xtfc-433de050-c66d-4f88-9ee8-c736f5176aad.png

Design A-122 was the largest and heaviest among the fast series of 32knots preliminary variants of the Tosa/Kaga having reaching more then 280m in length and 43.000+tons of displacement! Armour wise it continues the same layout begun with the first post-Nagato design of A-115. Based on the stats and available info this proposal might be the fast version of A-120 showing how much engine power (extra 33.000shp) and waterline length (extra 23meters) required to propel a ship from 56 to 59km/h!
With armament remains unchanged the extra length allows wide placement of the secondary casemated guns in the 1st deck.
The sheer size of the design clearly illustrates the requirements for high speed: Long sleek hull with large engine power

The design had the following characteristics:
Dimensions: 266,7 (pp) x 281 (wl) x 282,85 (oa) x 29,57 x 9,14 meters
Displacement: 43.500tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 157.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 59km/h (32knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official drawing:

Data table:

Normal speed proposals
A-123:

de3uyff-400a08f8-be1e-4b52-9a1c-dc6bda07cdc7.png

While A-121 and 122 were the fast versions of the Tosa preliminaries or more like fully armoured battlecruisers (like how the RN described HMS Vanguard! ) A-123 was a return to the acceptable size of the IJN shipyards and normal fleet speed of 50km/h or 27knots. Essentially A-123 was the slow version of the previous two proposals with a very similar casemated deck layout and turret arrangement.

The design had the following characteristics:
Dimensions: 213,36 (pp) x 227,08 (wl) x 229,51 (oa) x 30,48 x 9,14 meters
Displacement: 36.600tons (standard)
Armour: 229mm Belt inclined at 25 degrees, 76mm Deck, 51mm at Machinery 76mm at Magazine Slopes
Engines: 90.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 50km/h (27knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official drawing:

Data table:

Modified Mutsu proposals:
A-124:

de3sn5z-6050573b-d31c-4686-8704-e2b4e8dfaa1b.png

Design A-124 uses the same hull dimensions and main armament layout as A-123 but a on a different hull shape especially aft where it is more fuller and different casemated layout for the secondary 14cm guns moving most of them one deck up to provide better fire arcs and less effect from the ocean. Integrally the armour layout copies that of the Nagato with 305mm belt armour which weren't inclined contrary to A-123's 229mm and 25 degrees.
Another explanation about this design that it was the first version to modify and finish IJN Mutsu then under construction.

The design had the following characteristics:
Dimensions: 213,36 (pp) x 227,08 (wl) x 229,51 (oa) x 30,48 x 9,14 meters
Displacement: 37.200tons (standard)
Armour: 305mm Belt, 70mm Deck, 76mm Slopes
Engines: 91.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 50km/h (27knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official drawing:

Data table:

Comparison table between A-124, B-61, Fuso and Hiei:

Armour layout comparison:

Modified Design A-124' :
de3qijb-b57ddc77-8686-4d6d-822c-1b4270c5e4b3.png

A-124' was a simple alteration of the previous A-124 design with the only change of 4 extra underwater torpedo tubes but consequently a 9m extra length 600tons more displacement and a mere 1.000shp more engine power to maintain the desired speed. Armour scheme remained the same, a half-all or nothing style where the belt only covers the machinery and magazine spaces but the deck armour goes all the way to the ship ends. The closely spaced twin funnel arrangement remained the same as on A-124 and no other visible serious changes made.

The design had the following characteristics:
Dimensions: 222,5 (pp) x 236,2 (wl) x 238,66 (oa) x 30,48 x 9,14 meters
Displacement: 38.800tons (standard)
Armour: 305mm Belt, 70mm Deck, 76mm Slopes
Engines: 94.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 50km/h (27knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Underwater and 4x Above Water Torpedo Tubes

Official drawing:

Comparison table between A-124', B-61, Fuso and Hiei:

Armour layout comparison:

A-125:
de3oeoq-c5b25f18-d06b-4345-b746-fbc6437fe79c.png

Originally the Nagato class of the IJN was only considered as a single ship class consisting of only Nagato as the Diet of Japan 1916 did not vote for a new pair of battleships only a single one which became Nagato and two Battlecruisers which later became IJN Amagi and IJN Akagi. But later that year, at the end of the summer, the then American president Thomas Woodrow Wilson announced the 1916 Naval Act or "Big Navy Act" which meant the USN had to aquire 10 new battleships and 6 new Battlecruisers (4 Colorado, 6 South Dakota and 6 Lexington class capital ships) among other vessels, the parliament of Japan had no choice but to vote for 3 new battleships which became IJN Mutsu, IJN Kaga and IJN Tosa.
This pause allowed the designers to improve the Nagato class while remaining in the same tonnage level as that ship and by June 1917 a modified design was born with 5 turrets arranged as the later Tosa/Kaga class yet on a smaller hull then those of the later class.
There must had been debates of to what design Mutsu's construction must be based on, a repeat Nagato, an improved Nagato with 5 turrets similar to the Tosa/Kaga class then under design process or as a 3rd sister of that new class. Finally the choice was set on a repeat Nagato as it seems, because it would reduce costs of the overall new construction programme (1+1 Nagato and 2 Tosa VS 1 Nagato and 3 Tosa) and also that this way the Nagatos could form a heterogeneous squadron.
This and the fact there were lack of money to order the ship led to Mutsu being laid down a year later then Nagato in 1918 June despite the Yokosuka Naval Arsenal's Shipyard was free at that time. (Yamashiro was launched in 1915)
As you can see the chosen design for the 5 turret Nagato was much different from Nagato herself, the hull was more streamlined flush deck, no risen forecastle, but rather a flared bow eg the deck was constantly rising in height from the centre of the ship to the point of the nose. Improvements in engine technology allowed the same amount of shp to be mounted in a reduced space giving room to the 5th turret and trunking the boiler uptakes into a single funnel, though the casemated 1st and 2nd deck had to be reworked and the boat stowage became somewhat cramped as a result.

The design had the following characteristics:
Dimensions: 201,35 (pp) x 213,3 (wl) x 215,8 (oa) x 32,76 x 9,0 meters
Displacement: 33.800tons (standard)
Armour: 305mm Belt inclined to 25 degrees, 70mm Deck, 76mm Slopes
Engines: 80.000shp Gihon Steam Turbines, 4 shafts
Range: 10.200km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
16x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 53cm Above Water Torpedo Tubes

Official drawing:

Data table with comparison of Nagato:

Weight table:

Various calculations:

Leading proposals to Tosa/Kaga:
A-126 series:
Baseline:

de3m6ol-a55ac615-c5d2-4043-86d5-0cf0a7ae9660.png

A-126 is the baseline of the next series of designs. It has the same main turret layout as A-125 but the armour layout and thickness was vastly improved but to maintain speed the hull had to lengthened together with a 10% increase in engine power from 80.000 to 88.000shp. On the other hand A-125 was described as a modified Mutsu (despite the hull shape was not that of the Nagato but the dimensions are the same) A-126 shows a much different hull shape. Another unique feature of this design and the consequent proposals were to usage of large circular funnel.

The design had the following characteristics:
Dimensions: 213,36 (pp) x 227,07 (wl) x 228,4 (oa) x 32,7 x 9,3 meters
Displacement: 39.300tons (standard)
Armour: 292mm Belt inclined to 16,5 degrees, 102mm Deck, 76mm Slopes
Engines: 88.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawing:

Armour layout:

Turret arrangements:

Variant A:
de3k0dh-f8faa71d-6dba-4556-90ee-ca7daa0d49bf.png

Variant A was the most distinguishable design of the A-126 series. By placing the 3rd turret between the boilers and turbines essentially separating the two which provides protection, this arrangement meant that the turret had to be risen on the same height as the 2nd and 3rd to provide space for the ship's boat stowage. This resulted in the unique layout of the 1st deck separated by the 3rd turret's barbette yet not connected to it like on Amagi and Kii and also the hull was required to be lengthened by a few meters.

The design had the following characteristics:
Dimensions: 214,88 (pp) x 228,60 (wl) x 230,2 (oa) x 32,7 x 9,3 meters
Displacement: 39.000tons (standard)
Armour: 292mm Belt inclined to 16,5 degrees, 102mm Deck, 76mm Slopes
Engines: 91.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawing:

Armour layout:

Turret arrangements:

Variant B:
de3hujv-7d3cbf51-ceeb-469f-8de8-121ad8ab155f.png

Variant B was more reminiscent of the baseline A-126 design with the 3rd turret facing forward then to the A variant where the 3rd turret was placed on an elevated position between the funnel and the mainmast. On the other hand here the 3rd turret had wider spacing from the aft pair and thus drastically reducing the effect of a lucky hit disabling all 3 turrets aft. The 1st deck was also mimicking the baseline design in both shape and arrangement.

The design had the following characteristics:
Dimensions: 213,36 (pp) x 227,07 (wl) x 229,5 (oa) x 32,7 x 9,3 meters
Displacement: 39.650tons (standard)
Armour: 292mm Belt inclined to 16,5 degrees, 102mm Deck, 76mm Slopes
Engines: 90.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawing:

Armour layout:

Turret arrangements:

Variant C:
de3g1fa-a7486d1f-b411-401c-b58e-63a6c16b771a.png

Variant C was the 3rd sub version of the A-126 design where the 3rd turret was arranged reminiscent of the final design and of the consequent classes (Amagi, Kii ) eg facing aft. The 1st deck shape and arrangement was also different from the baseline A-126 and from the previous B variant and was used as a basis for the next design of A-127. The large circular shaped funnel still remains but the armour layout follows that of the A variant.

The design had the following characteristics:
Dimensions: 213,36 (pp) x 227,07 (wl) x 229,5 (oa) x 32,7 x 9,3 meters
Displacement: 39.650tons (standard)
Armour: 292mm Belt inclined to 16,5 degrees, 102mm Deck, 76mm Slopes
Engines: 90.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawing:

Armour layout:

Turret arrangements:

Final Pre-Design A-127:
de3dxvz-0f544e6e-d084-4942-bf90-b325626ec2ff.png

While many sources states that the design number A-127 was for the Kaga/Tosa class, the documents, drawings and data tables in the Yuzuru Hiraga archive states otherwise. Design A-127 while having all the major characteristics of the final Tosa class as laid down like the number of torpedo tubes primary, secondary and AA guns number position and arrangement there are subtle structural differences not to mention A-127 was shorter by a few meters. If you put the two drawings next or above each other these differences will show. But apart from the length of the hull the most prominent difference was the usage of the circular funnel first appeared in the A-126 series but was finally remodelled sometime later. Less noticeable but still distinct are the 1st deck shape mostly around the casemates and around the blast shields aft.

The design had the following characteristics:
Dimensions: 214,88 (pp) x 238,6 (wl) x 231,1 (oa) x 30,5 x 9,4 meters
Displacement: 39.900tons (standard)
Armour: 280mm Belt inclined to 15 degrees, 102mm Deck, 70mm Slopes
Engines: 91.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawing:

Armour layout:

Turret arrangements:

Final Tosa/Kaga Design as laid down:
de3bbui-9d67ba10-7f36-4afd-8105-c1bbc6f9f585.png

Part of the 8-8 construction programme, this was the final design accepted for construction as the follow up battleship class to the Nagatos and named Kaga class though Tosa was laid down earlier and hence often called Tosa in a number of sources. The class could be seen as a 5 turreted lengthened and improved version of Nagato incorporated many changes into the design but the flush deck design, 5th turret, one funnel and armour layout shows otherwise. The improvement in engine technologies during WW1 resulted in a 15% increase in shp to mount in around the same space as on Nagato, the armour belt while was thinner of only 280mm it was inclined hence providing better protection over longer ranges. Firepower seems to be the accepted standard for Post WW1 IJN as not just Kaga/Tosa, but the Amagi and Kii classes too would wield the same 10 gun broadsides in 5 twin turrets.
Often the design number A-127 was associated with the Tosa / Kaga class but from the Hiraga archives it is evident that 127 and Kaga are two different designs. Indeed A-127 was used as the very basis for the final Kaga class there are a number of differences between the two, Kaga/Tosa having oval shaped funnel, 3m longer hull and differently arranged torpedo tubes apart form a number of minor structural differences.

The design had the following characteristics:
Dimensions: 217,93 (pp) x 231,65 (wl) x 234,1 (oa) x 30,5 x 9,4 meters
Displacement: 39.900tons (standard), 44.200 (full load)
Armour: 280mm Belt inclined to 15 degrees, 102mm Deck, 76mm Slopes
Engines: 91.000shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
Speed: 49km/h (26,5knots)
Armaments:
5x2 410mm/45 Type 3 / 3rd Year Type Cannons,
20x1 140mm/50 Type 3 / 3rd Year Type Guns,
4x1 76mm/40 Type 3 / 3rd Year Type AA Guns,
4x1 61cm Above Water and 4x1 Underwater Torpedo Tubes

Official drawings:

Data table with connection of a proto-Kii design:


Extra Design:
Modified Kaga/Tosa, Kii Preliminary:

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Based on a documet I've found in the Yuzuru Hiraga archive of the University of Tokyo I might had found the very first incarnation of what became the Kii class Battleships of the IJN 1920/21. The document shows the general characteristics of the Tosa / Kaga class battleships with most elements ruled over and overwritten with different values. What made me think that it is connected to the Kii that the hull size, armour and engine power both almost identical that of the final Kii class. On the other hand both Kii and Amagi are extremely similar to each other so it is maybe had some connection with the Amagi class Battlecruisers as well.
Based on the data I concluded that this would be a lengthened faster version of the Kaga or Tosa class with two funnels, reduced casemated armament but almost 50% more engine power to gain 3,5knots extra speed. Due to the extra length and thus larger hull surface area and to not drastically increase the displacement the armour was thinned to 256mm Belt, 95mm Deck and 64mm Slopes from the original 280, 102 and 76mm!

This modified design clearly shows that achieving high speeds on capital ships is a very demanding endeavour: Providing an extra 50% engine power and a whopping 18,5m extra waterline length only proved enough for 30knots (from the base 26,5knots). A further two knots speed might even require minimum twice the powerplant of the Tosa and a likely extra 10m length!

The design had the following characteristics:
Dimensions: 234,7 (pp) x 249,93 (wl) x 252,37 (oa) x 30,78 x 9,45 meters
Displacement: 41.000tons (standard)
Armour: 256mm Belt inclined to 15 degrees, 95mm Deck, 64mm Slopes
Engines: 131.200shp Curtis Steam Turbines, 4 shafts
Range: 12.000km at 30km/h (5.500nm at 16knots)
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
Equipment allocated for Observation Balloon(s)

Data table with connection of a proto-Kii design:
 

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