Cruiser Projects and Designs of the IJN

[Tzoli]

Regarding the Improved Takao, or Takao-Kai, I've thought about it a little.
The official info states the same main armament as Takao but with the new twin 12,7cm Type 89 DP-AA guns likely in twin mounts. It would be likely that the torpedo armament too would had been enhanced with 4 triple rather then twin tubes.
But without the LNT I constrains it is not impossible that these cruiser would get the new improved no.3 /55 calibre 20cm guns.
To provide weight for these changes the Bridge structure might had been changed to that either of the Mdoernized Takaos or what was envisioned for the Mogamis a reduced size Castle bridge. Further weight savings could be gained by using the boilers eventually installed in the Mogamis. Takao had 12 Kampon boilers for 130.000shp while Mogami only required 10 for 152.000 and 8 in Suzuya so for the same 130.000shp 8 Mogami style boilers might suffice and likely result one less funnel, further reducing weight which could be allocated for the armament changes and likely some armour thickening.
Main armament wise we could either think the Myoko-Takao style one or what was introduced on the Mogamis.

 

[Tzoli]

Regarding the Tone-Kai or Improved Tone class cruiser design.
Based on experience what would you guys change on the original Tone design? It should be noted that this Improved Tone too would be a scout heavy cruiser so aircraft facilities aft and main guns forward. You have 1.800tons more displacement to play with. What would you change?

 

[Tzoli]

Here, I present you, to my knowledge the very first interpretation of this design!

Takao-Kai Type Heavy Cruiser by Tzoli on DeviantArt

www.deviantart.com

A few days before the first two units of the Takao class, IJN Takao and Atago laid down in early April 1927, the President of the United States, John Calvin Coolidge Jr. authorised the construction of 6 heavy cruisers (The Northampton class) as part of the first Cruiser Law and somewhat later that year after the failed Geneva Disarmament Conference he asked the Naval authorities of the US to prepare construction plans which could bring the USN in parity with the British Royal Navy. These events created an upheval in the Japanese Government and among the Admirals of the Navy the Vice Chief, Admiral Nomura Kichisaburo appointed a committee to discuss these recent events and draw up construction plans to counter the proposed expansion of the USN.
As part of this committee, the envisioned new fleet of the IJN should consist of 9x Battleships, 4x Aircraft Carriers, 12x 10.000ton large and 12x medium sized cruisers, 64 large and 32 medium destroyers and 65 submarines. The report created by the committee was presented to the Navy Ministry in 1928 and after a number of revisions the 4th proposal was accepted in May 1929 which envisioned the construction of the following types:
4 new 35.000ton Battleships (Kongo Replacement type)
4 new 10.000ton Heavy Cruisers (Takao-Kai)
12 new 1.400ton Destroyers
28 new 1.000ton Destroyers
2 new 1.900ton Submarines
10 new 1.600ton Submarines
18 new 800ton Submarines
13 new Auxiliary Vessels.

From this last plan born the requirement of new heavy cruiser design based that of the previous and then under construction Takao class and labelled Takao-Kai or Improved Takao design. The requirements as follows:
- More than 8x 20cm Main guns in High angle mounts
- Minimum 4x 12,7cm AA guns of new design (Type 89)
- Minimum of 4 twin 61cm torpedo tubes, 2 per side
- Maximum speed of at least 33knots and a range of 8.000nm at 14knots
- Protection of Machinery and Magazines spaces of direct hits from 15,5cm guns and indirect hits of 20cm guns
- Improved underwater defence

Apart from these requirements there was very little extra info available from Japanese sources. I've based my drawing on the Takao class but modified it accordingly, and taken ideas from the Mogami as laid down aka, enlarged deck structure around the 4th turret, simplified and reduced sized Castle like bridge I've also included somewhat more weaponry which is in the area of reality as the Admiralty always asked that a new warship design must be better then the previous one hence the twin 12,7cm AA and the new 20cm/55 guns. To save some weight I've thought using the Mogami style boilers which produced more steam with actually fewer boilers (Takao 12 boilers for 130.000shp, Mogami: 10 boilers for 152.000shp) saving weight on machinery and using the smaller bridge structure, this way I hope the extra armament weight was compensated somehow.

The design had the following characteristics:
Dimensions: Unknown I've chosen the hull of Takao: 192,5 (pp) x 201,7 (wl) x 203,8 (oa) 19 x 6,3 meters
Displacement: Unknown, around 11.000tons (standard)
Engines: 130-152.000shp Kampon Steam Turbines, 4 shafts
Range: 15.700km at 26km/h (8.500nm at 14knots)
Speed: 61km/h (33knots)
Armour: Unknown, likely Mogami style so 102mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 47mm over Magazines Deck, 32-60mm Slopes
Armaments:
5x2 20cm/55 Type 93 Guns
4x2 12,7cm/40 Type 89 DP-AA Guns,
4x1 40mm/39 14th Year Type HI AA Guns,
4x2 or 4x3 610mm Torpedo Tubes
3x Seaplanes: Kawanishi E7K Alf and Nakajima E8N Dave

 

[isayyo2]

Regarding the Tone-Kai or Improved Tone class cruiser design.
Based on experience what would you guys change on the original Tone design? It should be noted that this Improved Tone too would be a scout heavy cruiser so aircraft facilities aft and main guns forward. You have 1.800tons more displacement to play with. What would you change?

Broaden the beam a few feet and develop a three-gun turret to replace the four dual turrets with three triples. Reinvest the remaining displacement in light AA?

 

[Tzoli]

I have a question regarding the Torpedo Launchers of the IJN.
Do we have data or pictures about how far the IJN 61cm launchers or Torpedo turrets fire their torpedoes before hitting the water? Eg what is the maximum distance one can put these launchers from the edge of the deck?
The largest distance I could find was of Agano which carried two quad launchers on the centreline with a hull width of 15,2m eg 7,6m from the deck edge to the pivot of the mount and the nose of the torpedoes was likely around 5m from the edge. (61cm Type 90 torpedoes length was 8,55m) Aoba had a modification after battle damage and one of her launchers were put to the centreline and she was 15,8m wide.

Now it was stated that the Ibuki was considered for modification before launch: removal of the aircraft facilities and torpedo armament (4x4 61cm) and replace them with 5x5 torpedo launchers 2 per side 1 one the centreline (Eric Lacroix states the same launchers as used on Shimakaze not sure if the open launchers or the enclosed turrets). Now Ibuki had a hull width of 21,2 meters, which is 6 meters wider than Agano and an extra 3-3 meters both sides.

Now could these launchers launch their torpedoes to a distance of 8-10 meters before hitting the edge of the deck?

 

[Hood]

It seems unlikely to be able to fling them that far. Of course it's possible the centreline mount was nearer the fantail where the beam is narrower.

 

[Tzoli]

I thought so. Either to place it on an elevated position, put it on a rail so it could be moved to the appropriate firing side, or place it to the aft section.

 

[Tzoli]

Now I present the Mogami class as laid down:

Mogami Class as Laid Down by Tzoli on DeviantArt

www.deviantart.com

Originally before the 1st London Naval Treaty modified the Cruiser Construction allowance of the signatory navies, the IJN intended to build 4 improved or modified Takao class heavy cruisers. But the treaty introduced the tonnage system which drastically limited the construction of new cruisers for each navy and introduced a new type, the Light Cruiser which armament shall not exceed 155mm's. This resulted the cancellation of the Improved Takao class because the then finishing construction of the four 10.000ton units of the Takao class: IJN Takao, Atago, Maya and Chokai will reach the allowed tonnage for Category A - Heavy Cruiser tonnage of the IJN, Category B or Light Cruisers allowed tonnage was 100.450tons though for the IJN only 2.035tons remained for new construction. On the other hand the treaty allowed the signatory nations to expand their cruiser force by building modern units replacing the aging vessels, for IJN this meant the replacement of the IJN Tone and the 3 Yahagi class protected cruisers, the two Tenryu class vessels would reach overage by 1935 and IJN Kuma and Tama by 1936 and IJN Kitakami, Oi and Kiso by 1937. This freed up 50.955tons for new cruiser construction and the Naval General Staff decided the best way to distribute it was to build 4x 8.500ton units before 1936 and 2x 8.450ton units as a follow-on, which resulted in the Mogami and Tone classes. The effect of the treaty meant that the previous naval programme had to be revised. This first revised 1930 programme distributed into two phases:
4+2x 8.500ton cruisers (Mogami and Tone Classes)
18+7x 1.400ton destroyers (Hatsuharu class)
1+0x 9.850ton Carrier
1+2x 1.900ton Submarines (Junsen II class)
6+2x 1.400ton Submarines (Kaidai VI class)
2+0x 700ton Submarines (Kaichu VI class)
After a number of revisions the 1930/31 final naval programme, known as Maru 1 Programme included the following:
4x 8.500ton cruisers (Mogami Class)
12x 1.400ton destroyers (Hatsuharu class)
1x 1.900ton Submarines (Junsen II class)
6x 1.400ton Submarines (Kaidai VI class)
2x 700ton Submarines (Kaichu VI class)

Now 8.500tons would be enough for a 8-9x 6" or 15cm armed cruiser with good speed and armour, but the Naval General Staff's requirements of
- 5x3 15,5cm guns (Able to be replaced by twin 20cm ones) with high angle of elevation,
- protection comparable that of the previous Takao class,
- 8.000nm at 14knots with a maximum speed of 37knots,
- Main task as of the previous 10.000ton type cruisers.
meant that these requests on a 8.500ton hull would be impossible to accomplish and quickly the designers added 1.000tons of displacement to bring the design in the realm of possibility to construct and thus by the summer of 1931 the basic design C-37 was born. The Mogami class as laid down had many similarites of the previous Takao class and likely borrowed ideas from that of the Takao-Kai design. The changes included more powerful turbines and reduced number but more powerful boilers from 12 to 10 units, revised armament layout, midship torpedo launcher arrangement and a reduced but still impressive Takao style bridge. The aircraft handing facilities together with the aircraft hanger aft would be quite similar to the Takao as well. While the torpedo tubes number increased from 4x twin to 4x triple mounts the Heavy AA guns too got strenghtened by introducing the new 12,7cm/40 AA guns which had better ballistic capabilities then the older 12cm ones.

The design had the following characteristics:
Dimensions: 189 (pp) x 197 (wl) x 20,6 x 6,1 meters
Displacement: 9.500tons (standard)
Engines: 152.000shp Kampon Steam Turbines, 4 shafts
Range: 15.100km at 26km/h (8.200nm at 14knots)
Speed: 61km/h (33knots)
Armour: 100mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 40mm over Magazines Deck, 60mm Slopes
Armaments:
5x3 15,5cm/60 Type 90 Guns
4x1 12,7cm/40 Type 89 DP-AA Guns,
4x1 40mm/39 14th Year Type HI AA Guns,
4x3 610mm Torpedo Tubes
3x Seaplanes: Kawanishi E7K Alf and Nakajima E8N Dave

 

[Tzoli]

Following is the Tone class as ordered, basically a slightly modified Mogami:

Tone Class as Ordered by Tzoli on DeviantArt

www.deviantart.com

Originally the 1930 Naval Programme included six 8.500ton light cruisers to be constructed in two phases: 4 in the first and 2 in the second. The second phase units were became the Tone class but as you can see here, their original idea was basically a lightly modified Mogami with twin rather then single 12,7cm DP-AA guns on an 50tons less displacement. But like the Mogamis original displacement of 8.500tons was not enough to carry the required specifications of the Naval Staff, a more heavily armed version surely more less so. Hence the Tone design displacement too risen by 1.000tons to the acceptable 9.450ton range, but to compensate the weight of the heavier twin 12,7cm mounts I think a Suzuya and later Tone style machinery arrangement of 8 slightly larger boilers instead of 8 large and 2 small ones as well as the usage of the lighter and smaller quad 13mm guns might be sufficient to achieve the desired tonnage.
Aesthetically apart from the twin 12,7cm shielded gun mountings I've replaced the Mogami funnel with that of the Tone, changed the orientation of the Catapults (and the aircrafts on them) as well as some slight superstructure changes here and there for it to look somewhat more distinct from that of the Mogami as laid down.

The design had the following characteristics:
Dimensions: 189 (pp) x 197 (wl) x 20,6 x 6,1 meters
Displacement: 9.450tons (standard)
Engines: 152.000shp Kampon Steam Turbines, 4 shafts
Range: 15.100km at 26km/h (8.200nm at 14knots)
Speed: 61km/h (33knots)
Armour: 100mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 40mm over Magazines Deck, 60mm Slopes
Armaments:
5x3 15,5cm/60 Type 90 Guns
4x2 12,7cm/40 Type 89 DP-AA Guns,
4x4 13mm/76 Type 93 AA Guns,
4x3 610mm Torpedo Tubes
3x Seaplanes: Kawanishi E7K Alf and Nakajima E8N Dave

 

[Tzoli]

Next is the Tone class as actually laid down:

Tone Class as Laid Down by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 190,3 (pp) x 198,8 (wl) x 201,6 (oa) x 19,4 x 6,2 meters
Displacement: 9.450tons (standard)
Engines: 152.000shp Kampon Steam Turbines, 4 shafts
Range: 15.100km at 26km/h (8.200nm at 14knots)
Speed: 61km/h (33knots)
Armour: 100mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 40mm over Magazines Deck, 60mm Slopes
Armaments:
4x3 15,5cm/60 Type 90 Guns
5x2 12,7cm/40 Type 89 DP-AA Guns,
4x2 25mm/60 Type 96 AA Guns,
2x2 13mm/76 Type 93 AA Guns,
4x3 610mm Torpedo Tubes
3x Seaplanes: Kawanishi E7K Alf and Nakajima E8N Dave

 

[awhalen61]

Next is the Tone class as actually laid down:

Tone Class as Laid Down by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: 190,3 (pp) x 198,8 (wl) x 201,6 (oa) x 19,4 x 6,2 meters
Displacement: 9.450tons (standard)
Engines: 152.000shp Kampon Steam Turbines, 4 shafts
Range: 15.100km at 26km/h (8.200nm at 14knots)
Speed: 61km/h (33knots)
Armour: 100mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 40mm over Magazines Deck, 60mm Slopes
Armaments:
5x3 15,5cm/60 Type 90 Guns
5x2 12,7cm/40 Type 89 DP-AA Guns,
4x2 25mm/60 Type 96 AA Guns,
2x2 13mm/76 Type 93 AA Guns,
4x3 610mm Torpedo Tubes
3x Seaplanes: Kawanishi E7K Alf and Nakajima E8N Dave

That centerline 5"/40 always gets me lol.

also, 4x3* not 5x3 155mm

 

[Tzoli]

Ahh thanks, fixed it. Well according to the description of Eric Lacroix the 5th 12,7cm mount was deleted because the surrounding structures and the mast hampered it's firing angle so I thought it was to be located near it.

 

[JFC Fuller]

Because the Hiraga document hinted 12 barrels so either 4 triple or 3 quad turrets hence this 4 turreted version I show here.
I'm not sure it is possible to mount 12 barrels on 10.000tons but the usual splinter protection of the Japanese cruiser gun turrets and the shorter belt and deck armour compared to the 5 turreted original Myoko together with some other weight saving might be just enough to reach that goal.
Reduced ammo for standard loadout fewer torpedo tubes and DP-AA guns might be necessary as well.

Original Documents:

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

Thank you for these Tzoli, these really are fascinating. I would love to know more about that 55 cal 8" gun, shame it is so obscure. On this 10,000 ton cruiser, having looked at the source documents you linked to there is no doubt this was meant as a twelve, not eight or nine, gun ship. The order of the document is a bit confusing, not helped by the various edits the author made (you can see where figures were rubbed or crossed out) but the basic outline of what was being considered is there. I have pulled out the key parts related to the armament below:

Pages 3 & 4: These are calculating the weights for the main armament and its associated armour scheme as well as barbette, and turret diameters etc. The author appears to be trying to establish whether quadruple (labelled IV) or triple (labelled III) gun turrets are more efficient, note what appears to be a crude calculation of weight per gun in the table at the top of page 3.

Page 2, bottom sheet: This is calculating total armament weight and then the total ship weight. Its confusing because in the table at the bottom left the author has crossed out the total weight for four triple gun turrets and replaced them with the total weight for three quadruple gun turrets. However, the number of guns is clear in the ammunition weight calculation (20 x 12 = 240) for both variants, I think the "(110)" in the margin is rounds per gun.

Page 6: This looks like it was edited more than once but what we see is the total armament weight for the four triple turret variant in the sum of weights. I think the 7,100 ton design it is being compared is the Aoba class. Note the additional 1,900 tons of oil, coal and reserve feed water that would go on top of the 7,100 ton's full displacement. It seems reasonable that a similar figure would apply to the 10,000 ton ship.

For the 12cm guns, the 2 is written over a 4, the original calculation was for 4 guns (as in the Aoba class). Subsequently, it was halved to 2 guns taking the secondary armament weight from 49 tons to 24.5 tons - rounded up to 25 tons.

It's interesting that the Japanese ultimately went in exactly the opposite direction to this with their five twin turret designs.

 

[Tzoli]

Because the Hiraga document hinted 12 barrels so either 4 triple or 3 quad turrets hence this 4 turreted version I show here.
I'm not sure it is possible to mount 12 barrels on 10.000tons but the usual splinter protection of the Japanese cruiser gun turrets and the shorter belt and deck armour compared to the 5 turreted original Myoko together with some other weight saving might be just enough to reach that goal.
Reduced ammo for standard loadout fewer torpedo tubes and DP-AA guns might be necessary as well.

Original Documents:

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

Thank you for these Tzoli, these really are fascinating. I would love to know more about that 55 cal 8" gun, shame it is so obscure. On this 10,000 ton cruiser, having looked at the source documents you linked to there is no doubt this was meant as a twelve, not eight or nine, gun ship. The order of the document is a bit confusing, not helped by the various edits the author made (you can see where figures were rubbed or crossed out) but the basic outline of what was being considered is there. I have pulled out the key parts related to the armament below:

Pages 3 & 4: These are calculating the weights for the main armament and its associated armour scheme as well as barbette, and turret diameters etc. The author appears to be trying to establish whether quadruple (labelled IV) or triple (labelled III) gun turrets are more efficient, note what appears to be a crude calculation of weight per gun in the table at the top of page 3.

Page 2, bottom sheet: This is calculating total armament weight and then the total ship weight. Its confusing because in the table at the bottom left the author has crossed out the total weight for four triple gun turrets and replaced them with the total weight for three quadruple gun turrets. However, the number of guns is clear in the ammunition weight calculation (20 x 12 = 240) for both variants, I think the "(110)" in the margin is rounds per gun.

Page 6: This looks like it was edited more than once but what we see is the total armament weight for the four triple turret variant in the sum of weights. I think the 7,100 ton design it is being compared is the Aoba class. Note the additional 1,900 tons of oil, coal and reserve feed water that would go on top of the 7,100 ton's full displacement. It seems reasonable that a similar figure would apply to the 10,000 ton ship.

For the 12cm guns, the 2 is written over a 4, the original calculation was for 4 guns (as in the Aoba class). Subsequently, it was halved to 2 guns taking the secondary armament weight from 49 tons to 24.5 tons - rounded up to 25 tons.

It's interesting that the Japanese ultimately went in exactly the opposite direction to this with their five twin turret designs.

Indeed! Yuzuru Hiraga played with triple and quad turrets way before this at the 1920's No.13 preliminary designs with triple 41cm and 46cm turrets as well as quad 41cm ones! As I've seen many Hiraga documents with his handwriting I'm sure these papers are created by himself and edited as he changed his mind.
I've asked about this on the NavWeaps forum:

NavWeaps Forums-Extra info for NavWeaps

It appears there were more gun development was done by the IJN that we know apart from the 41cm/45, 46cm/50 and 48cm/45 guns, the Hiraga archive provi

www.tapatalk.com

and TonyD's insight that the armament weight was too low for 3 quad or 4 triple turrets. He also suggests the choice of 5 twin turrets was the result of a requirement for a long and sleek hull to reach the desired high speed set by the Naval General Staff. And for that it is easier to mount 5 smaller diameter eg twin turrets then a fewer much larger diameter ones even if you had to lengthen the belt and deck armour considerably. On the other hand the fewer larger turrets would be already moved closer to the centre of gravity of the ship where the hull was already wider.

As for the 20cm/55 gun I would like to know more as well but sadly I only have the info from the Japanese Wiki article as finding English speaking Japanese Naval Enthusiasts is not an easy thing to do!

 

[Tzoli]

Here is my interpretation of the Design C-40 the Tone-Kai or Improved Tone type:

Design C-40 Tone-Kai Type Heavy Cruiser by Tzoli on DeviantArt

www.deviantart.com

The design had the following characteristics:
Dimensions: unknown, I've chosen 191,5 (pp) x 200 (wl) x 203 (oa) x 20,4 x 6,4 meters
Displacement: 13.000tons (standard)
Engines: Unknown likely 160-170.000shp Kampon Steam Turbines, 4 shafts
Range: 15.100km at 26km/h (8.200nm at 14knots)
Speed: 61km/h (33knots)
Armour: Unknown, likely 110-120mm over Machinery, 150mm over Magazines Belt, 40-45mm over Machinery, 50mm over Magazines Deck, 65-70mm Slopes
Armaments:
4x2 20,3cm/50 Type 90 No.2 Guns
4x2 10cm/60 Type 98 DP-AA Guns,
9x2 25mm/60 Type 96 AA Guns,
4x3 or 4x4 610mm Torpedo Tubes
Seaplanes: The Hanger storage has the capacity of:
3x Aichi E13A Jake
4x Aichi E16A Zuiun/Paul
5x Aichi E10A Hank
6x Mitsubishi F1M Pete
6-7x Nakasima E8N Dave
floatplanes, or a mix of these while there are two extra space on the catapults and roughly depending on aircraft size 5-8 more on the floatplane deck.

 

[Tzoli]

The Ibuki aka the modified Suzuya design:

Design C-46 Ibuki Class Heavy Cruiser by Tzoli on DeviantArt

www.deviantart.com

Due to budgetary and shipyard production capacity reasons the two modified Tone or Tone-Kai type heavy cruisers ordered in the Maru 4 Programme in 1938 July were cancelled sometime later in March 1939, instead priorities given to build Destroyer-squadron leader cruisers aka Agano class light cruisers. While these two 20cm armed cruisers were deleted from the programme the Naval General Staff did intended to include new construction of such cruisers in future programmes. In the 1941 May Conference the Naval General Staff accepted the Maru 5 Programme which included 159 new construction vessels and which was expected to be started as earliest as 1942 and would take around 8-9 years to complete with an expected finishing date of 1950. But due to the worsening international situation the expanded expenditure of the finance and planned fleet expansions of the USN, the Japanese had to change priorities and adopt a new construction programme which could be finished before 1944 April 1. This naval programme evolved into the Maru Kyu programme or Circle Urgent programme. The priorities in construction shifted as follows:
1. Naval Aircrafts
2. Submarines
3. Aircraft Carriers
4. Escort Vessels
5. Destroyers
6. Transport Ships
7. Cruisers
8. Battleships and Battlecrusiers
To speed up construction of the ordered vessels the usage of designs already constructed were to be used with modifications due to operational experience, in case of the cruisers the base type design became the Modified Mogami type, the Suzuya subclass.
This naval programme adopted in 1941, July 28 and ordered given to construct the vessels later that year in november with 2 cruisers included.
As mentioned above the new cruisers were to use an already existing design and likely ordered to replace the cancelled Tone-Kai ships. Provisional hull numbers were associated:
No.300 for IJN Ibuki and No.301 for her sister ship IJN Ikoma
The actual design were to be very similar that of the Suzuya type:
Same hull dimensions,
Same armament and layout (5x2 20cm)
Same AA armament of 4x2 12,7cm, 4x2 25mm and 2x2 13mm AA guns
Same Protection
Same Machinery
Improved Torpedo armament of 4x quadruple tubes
Placement of the mainmast near the 4th turret as on the Modernised Takaos
Slightly modified bridge structure with improved command facilities, added AA-Command platform and both the Compass bridge and AA-Command platform would had windscreens.

I've only improved the light AA a bit by the usage of 8 triple 25mm guns

The design had the following characteristics:
Dimensions: unknown, I've chosen 187,8 (pp) x 198,4 (wl) x 201,6 (oa) x 21,2 x 6,31 meters
Displacement: 12.500tons (standard), 14.800tons full load)
Engines: 152.000shp Kampon Steam Turbines, 4 shafts
Range: 13.900km at 26km/h (7.500nm at 14knots)
Speed: 61km/h (33knots)
Armour: Same as Suzuya: 100mm over Machinery, 140mm over Magazines Belt, 35mm over Machinery, 40mm over Magazines Deck, 60mm Slopes
Armaments:
5x2 20,3cm/50 Type 90 No.2 Guns
4x2 12,7cm/40 Type 89 DP-AA Guns,
8x3 25mm/60 Type 96 AA Guns,
4x4 610mm Torpedo Tubes
3x Seaplanes: Aichi E16A Zuiun/Pauls and Mitsubishi F1M Petes

 

[Tzoli]

For the time being my last IJN cruiser drawing, the Torpedo cruiser modification of the Ibuki:

Ibuki Class Torpedo Cruiser Modification by Tzoli on DeviantArt

www.deviantart.com

 

[_Sarcasticat_]

For the time being my last IJN cruiser drawing, the Torpedo cruiser modification of the Ibuki:

Ibuki Class Torpedo Cruiser Modification by Tzoli on DeviantArt

www.deviantart.com

It seems a little odd to me. Would they not have just removed the catapults, aircraft, and associated equipment while keeping the protective decking? Strafing is an issue, and the shields provide essentially no protection.
The centerline 61cm really irks me and I keep wondering why they placed it there.

I found this elsewhere.

However, the Naval General Staff had several points of contention with the design, with the fact that the four quadruple torpedo tubes were placed at the very stern of the ship - right above the propellers - being at the top of the list. Due to the squabbling between the Naval General Staff and the Naval Construction Corps, the design was shelved with the outbreak of war, but in February 1942, it was pulled out of mothballs and looked over once again. The designers managed to fix the placement of the torpedo tubes, and finally the design was approved in March 1942. The first ship (Ibuki) was laid down in April 1942.

This could be useful.

 

[Tzoli]

It seems a little odd to me. Would they not have just removed the catapults, aircraft, and associated equipment while keeping the protective decking? Strafing is an issue, and the shields provide essentially no protection.
The centerline 61cm really irks me and I keep wondering why they placed it there.

There is no drawing survived so far showing the torpedo launcher positions but that centreline position seems like a logical placement.
As for why I delete the aircraft platform: because the torpedo turrets are large, and this also frees up considerable weight.
Also here:

Ibuki Class Heavy Cruiser Design C-46 "Torpedo Modification Proposal" (1942)- While the Ibuki class IJN Ibuki and Ikoma hull numbers 300 and 301 were known cruiser based on the Suzuya, there was a proposal to change these heavy cruisers into more potent torpedo platforms. Though the description is rather vague how the torpedo launchers would had been placed, it was said that the original 4 quad launchers either to be replaced or even strengthened by 5 quintuple launchers, 2 per side one one centreline in place of the Aircraft handling facilities even deleting the Catapults themselves. This would had been provided a great deal of torpedo firepower rivaling that of the Kitakami and Oi's conversions with either 15 or 23 tubes per side!
Source: (Eric Lacroix - Japanese Cruisers of the Pacific War)

https://imgur.com/mn53S8w

View: https://i.imgur.com/mn53S8w.png

https://imgur.com/hCWl8Jn

View: https://i.imgur.com/hCWl8Jn.png

I found this elsewhere.

However, the Naval General Staff had several points of contention with the design, with the fact that the four quadruple torpedo tubes were placed at the very stern of the ship - right above the propellers - being at the top of the list. Due to the squabbling between the Naval General Staff and the Naval Construction Corps, the design was shelved with the outbreak of war, but in February 1942, it was pulled out of mothballs and looked over once again. The designers managed to fix the placement of the torpedo tubes, and finally the design was approved in March 1942. The first ship (Ibuki) was laid down in April 1942.

This could be useful.

That description, especially the torpedoes placed on the very stern of the ship looks like part of the discussion of this fantasy design and has nothing to do with the Ibuki:

The first C-41-43 was from the Hiraga Archive and likely Hiraga's own designation. The later C-43 was the one I'm talking about.

That cruiser with 4x3 turrets was from this article:

and which already made into the WoWs as Zao (Originally Senjo or Unzen).

Officially we only know that 20cm cruisers were planned for the 1940 or 41 programmes. I've not yet found any other info about this cruiser. I've heard a rumor that Wargaming found evidence or even documents on them but I'm very skeptic about this.

 

[_Sarcasticat_]

It seems a little odd to me. Would they not have just removed the catapults, aircraft, and associated equipment while keeping the protective decking? Strafing is an issue, and the shields provide essentially no protection.
The centerline 61cm really irks me and I keep wondering why they placed it there.

There is no drawing survived so far showing the torpedo launcher positions but that centreline position seems like a logical placement.
As for why I delete the aircraft platform: because the torpedo turrets are large, and this also frees up considerable weight.
Also here:

Ibuki Class Heavy Cruiser Design C-46 "Torpedo Modification Proposal" (1942)- While the Ibuki class IJN Ibuki and Ikoma hull numbers 300 and 301 were known cruiser based on the Suzuya, there was a proposal to change these heavy cruisers into more potent torpedo platforms. Though the description is rather vague how the torpedo launchers would had been placed, it was said that the original 4 quad launchers either to be replaced or even strengthened by 5 quintuple launchers, 2 per side one one centreline in place of the Aircraft handling facilities even deleting the Catapults themselves. This would had been provided a great deal of torpedo firepower rivaling that of the Kitakami and Oi's conversions with either 15 or 23 tubes per side!
Source: (Eric Lacroix - Japanese Cruisers of the Pacific War)

https://imgur.com/mn53S8w

View: https://i.imgur.com/mn53S8w.png

https://imgur.com/hCWl8Jn

View: https://i.imgur.com/hCWl8Jn.png

Going by previous conversations on the topic, it's probably the only place it could go.

Look closely. "Before the launch of Warship No. 300 (Ibuki) there was a plan at the end of 1942 to disembark the aircraft equipment and to install five quintuple torpedo-tube mounts, two on each side and one on the centerline, to get a broadside of fifteen tubes."
It states only the removal of aircraft equipment (and their associated aircraft, obviously) but nothing more. The torpedo mounts within the superstructure are not shielded, but Lacroix/Wells do state they're exactly identical, although I do not know if the Japanese would distinguish between shielded and unshielded. I don't exactly expect them to keep the shield on the one going to replace the two in the superstructure, though, so perhaps not exactly identical.
I do believe that the platform would remain. Not only does it provide for anti-aircraft weapon installations above, but it also serves to protect the mounts and their equipment as intended. Regardless, you get nearly 100 tonnes to play with for what you remove.
I'm not going to pretend to understand where exactly they intend to place the centerline TT outside of aft where the hull thins down. Perhaps it'll just remain there. Maybe it was an oversight: "eh, we'll just put one amidships" without really thinking about how jank that would be at first.

 

[M. A. Rozon]

I do believe that the platform would remain. Not only does it provide for anti-aircraft weapon installations above, but it also serves to protect the mounts and their equipment as intended. Regardless, you get nearly 100 tonnes to play with for what you remove.
I'm not going to pretend to understand where exactly they intend to place the centerline TT outside of aft where the hull thins down. Perhaps it'll just remain there. Maybe it was an oversight: "eh, we'll just put one amidships" without really thinking about how jank that would be at first.

In my mind, I had always pictured the centreline torpedo tube mount amidships atop the platform overhead the four mounts already there. However, there would have to be some care taken to insure the arcs were clear enough to allow for the vertical drop of the torpedoes once they left the tubes. This might require one or more of the following:

1) the height of the mount increased by using a pedestal of some kind at it's base;
2) larger charge to expel the torpedo at a higher velocity to clear the structure;
3) reduction in firing arc forward and abaft the beam;
4) placing the mount on a track to move it closer to the engaged side to ensure clearance of the ship's structure by the torpedoes as they are launched. There is a precedent for such an installation as the Nagato and Mutsu (and many of the other 8-8 designs IIRC) initially had such tracks for the rangefinder positions on their forward tower. Edit here to correct grammar after original post.

Just some thoughts.

 

[Tzoli]

I've thought of the 4th but look at how big these launchers!

 

[M. A. Rozon]

I've thought of the 4th but look at how big these launchers!

Indeed, the launchers are large and heavy but, based on previous experience for the IJN, they don't have to move very quickly or very far to get into position. A minute (two at the outside) would suffice to get them into position on the engaged side.

 

[_Sarcasticat_]

I've thought of the 4th but look at how big these launchers!

Indeed, the launchers are large and heavy but, based on previous experience for the IJN, they don't have to move very quickly or very far to get into position. A minute (two at the outside) would suffice to get them into position on the engaged side.

That's actually a pretty neat idea. Logic tells me the larger propulsive charge is more likely, but goddamn the mount track idea is a good one.

 

[tom!]

Hi.

Is there a list of all cruiser proposals and designs by design number? Including designs without available details?

C-46 implicates that there were at least 46 main designs....

Yours

tom!

 

[Tzoli]

Here:

Battlecruisers:

B-12 - Tsukuba class (1904)
B-15 - Ibuki/Kurama class (Kurama) (1904)
B-17 - Ibuki/Kurama class (Ibuki) (1906)
B-39 - Kongo Preliminary (1909) 29.000tons 4x2 356mm
B-40 - Kongo Preliminary (1909) 26.000tons 3x2 356mm
B-41 - Kongo Preliminary (1909) 25.000tons 3x2 305mm
B-42 - Kongo Preliminary (1909) 26.800tons 3x3 305mm
B-43 - Kongo Preliminary (1909) 30.000tons 4x3 305mm
B-44 - Kongo Preliminary (1909) 26.500tons 3x3 305mm
B-45 - Kongo Preliminary (1909) 26.500tons 4x2 305mm
B-46 - Kongo Preliminary (1910) 26.000tons 4x2 305mm
B-46 mod - Kongo class (1910)
B-48 - Modified Kongo? (1911) 26.000tons 4x2 356mm
B-58 - Amagi Preliminary (1919) 32.600tons 4x2 410mm
B-59 - Amagi Preliminary (1919) 34.200tons 4x2 410mm
B-60 - Amagi Preliminary (1919) 34.900tons 4x2 410mm
B-61 - Amagi Preliminary (1919) 36.600tons 4x2 410mm
B-62 - Amagi Preliminary (1919) 39.900tons 4x2 410mm
B-62A - Amagi Preliminary (1919) 40.000tons 4x2 410mm
B-62B - Amagi Preliminary (1919) 40.000tons 4x2 410mm
B-62C - Amagi Preliminary (1919) 44.000tons 4x2 410mm
B-62D - Amagi Preliminary (1919) 46.000tons 4x2 410mm
B-62E - Amagi Preliminary (1919) 35.000tons 4x2 410mm
B-62F - Amagi Preliminary (1919) 35.000tons 4x2 410mm
B-63 - Amagi Preliminary (1919) 41.000tons 5x2 410mm
B-64 - Amagi class (1919)
B-65 - Kii class Battleship? (1921)
B-65 - Large Cruiser design - Super Type A Cruiser (1941) 32.000tons 3x3 310mm
B-65 - Large Cruiser revised design - Super Type A Cruiser (1942?) 34.800tons 3x2 356mm


1st and 2nd Rate Cruisers:

C-7 - Tone class Protected Cruiser (1903)
C-18 - Chikuma class Protected Cruiser (1907)
C-19 - Minelayer Cruiser design (1912) 6.000tons 4x1 152mm
C-26 - Tenryu class? (1915) Tenryu Preliminary? (1915)
C-31A - Light Cruiser design (1915) 7.000tons 9x1 140mm
C-32 - Tenryu Preliminary (1915) 4.100tons 5x1 140mm
C-33 - Tenryu class? (1915) Kuma class? (1917)
C-37 - Mogami class Light/Heavy Cruiser (1931)
C-38 - Tone class Light/Heavy Cruiser (1934)
C-39 - Agano Preliminary (1938) 7.800tons 3x2 152mm
C-40 - Maru 4 Programme Type A cruiser design? Tone-Kai?
C-41 - Agano class (1939)
C-42 - Oyodo class (1939)
C-43 - Unknown Cruiser Design (Heavy Cruiser Design?)
C-44 - Agano-Kai design (1940) 8.250tons 4x2 152mm
C-45 - AA cruiser design (1942?) 5.800tons 4x2 100mm
C-46 - Ibuki class Heavy Cruiser (1941)
Out of sequence from the Hiraga archive:
C-41 - Heavy Cruiser design / Myoko preliminary? (1923) 14.000tons 4x2 203mm
C-42 - Heavy Cruiser design / Myoko preliminary? (1923) 12.000tons 4x2 203mm
C-43 - Squadron Leader Cruiser design (1923) 5.600tons 4x2 140mm

3rd Rate Cruisers:

D-1 - Niitaka class Protected Cruisers (1897)
D-2 - Otawa class Protected Cruiser (1897)

Gunboats/Escort Ships/Dispatch Vessels:

E-4 - Yodo class Dispatch vessels / small protected cruisers (1905)
E-6 - Mogami Dispatch vessel / small protected cruiser (1905)

Destroyers:

F-42 - Yubari class Light Cruiser (1921)

Auxiliary Ships:

J-16 - Katori class training cruiser (1937)

 

[tom!]

Hi.

Thx, I´ve seen that impressive list at your blog.

Any ideas about the missing ones?

Yours

tom!

 

[Tzoli]

Hi.

Thx, I´ve seen that impressive list at your blog.

Any ideas about the missing ones?

Yours

tom!

Blog? I don't have a blog!
Maybe in some unfound IJN documents. Weirdly there are extensive kbowledge in Hiraga archive about the Furutakas and Myokos yet no design number I've found mentioned!

 

[tom!]

Hi.

Thx for the reply. Sorry for the blog-error. I´ve ment your publications at deviantart...

Looks like another work to be done.

Yours

tom!

 

[Tzoli]

I think I've finally found the original document and drawing showing the outline of the Mogami's Takao style bridge as designed!
Hiraga document number: 21090501

平賀譲デジタルアーカイブ · 〔断面図〕 · 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

 

[lancer21]

Gorgeous drawings (and cruisers!), thank you Tzoli. Regarding the Tone-kai, the addition of the hangar and superfiring turrets are your own interpretation, there isn't any info to suggest those changes? The enclosed hangar certainly makes sense since Oyodo had such.
Regarding the main gun arrangement, how about having C turret superfiring over D, but still facing backwards? Or it would be a worse arrangement compared to your proposal?
In either case, with the hangar and superfiring turrets there is an increase in top weight, but presumably the hull is slightly wider/longer to accomodate it, hence the 13,000 tons displacement.

 

[Tzoli]

Gorgeous drawings (and cruisers!), thank you Tzoli. Regarding the Tone-kai, the addition of the hangar and superfiring turrets are your own interpretation, there isn't any info to suggest those changes? The enclosed hangar certainly makes sense since Oyodo had such.
Regarding the main gun arrangement, how about having C turret superfiring over D, but still facing backwards? Or it would be a worse arrangement compared to your proposal?
In either case, with the hangar and superfiring turrets there is an increase in top weight, but presumably the hull is slightly wider/longer to accomodate it, hence the 13,000 tons displacement.

It's my own addition as the info on this project is extremely limited.
The 2nd superfiring turret does increase topweight but among the heavy cruisers the Tone class was considered the most stable and the crew liked them so I doubt this design would had issue as well.
I've played with several layouts, though not that much is possible:
1. O=o=O=o=
2. O=o=o=o=
3. O==oO=o=
4. o=o=O=o=
5. o==oO=o=
6. o==OO=o=
7. =o=oO=o=
8. =o=OO=o=

But stayed with the current one as it allowed moving the magazines closer to the centre of the ship and reduce the belt armour length to save weight.

 

[lancer21]

Thanks again for your insight, fascinating as always (and more fuel to various IJN what-ifs!).

Regarding the previously mentioned 20cm/55 Mod. 3 gun, surprised they haven't build them at least to use for the Mogamis rearming and the Tones, since the IJN was looking for any advantage they could get.

 

[Tzoli]

Thanks again for your insight, fascinating (and more fuel to various IJN what-ifs!). Regarding the previously mentioned 20cm/55 Mod. 3 gun, surprised they haven't build them at least to use for the Mogamis rearming and the Tones, since the IJN was looking for any advantage they could get.

It was built and tested but further development cancelled due to budgetary reasons.

 

[Colonial-Marine]

It was probably determined the performance improvement wasn't worth the cost at that time, or that enough of a benefit could be gained just switching from the 200mm No. 1 to the 203mm No. 2 gun with less complications when switching existing ships to the new gun.

 

[biber550]

Dear Tzoli! I really like your reconstruction of this big light cruiser, but I will carefully express my opinion - both the cruiser Kako and the next cruiser Furutaka have gun magazines located at the ends and guns are grouped there. It's good enough to suggest that this cruiser has the same thing, and if we assume that it was developed very close to Furutaka, then the design could be closer to her. I will not insist - there is too little data and your reconstruction is quite correct.

Moderator Edit: Removed lengthy quote of entire post. Please highlight snippets that you wish to quote so everyone is clear what you are referring too.

 

[Tzoli]

Erm.... which design? You seem to quote my entire first post so I don't know what design you referring at!

 

[biber550]

Erm.... which design? You seem to quote my entire first post so I don't know what design you referring at!

Big light cruiser.

 

[Tzoli]

Erm.... which design? You seem to quote my entire first post so I don't know what design you referring at!

Big light cruiser.

You mean Design X? If you checked the post I've included the original official document which included the Hiraga drawing as well showing clearly where the magazines are located compared to the turrets. Even the superstructure elements are present:
Small bridge superstructure forward (Reminiscent of the Nagato, Tosa, Amagi and Kii classes) with tripod mast, aft tripod mainmast and blast shields to protect the 14cm gun and ship boats. I don't see much commonality with the Kuma and Furutaka classes. Hull shape maybe.

 

[biber550]

Erm.... which design? You seem to quote my entire first post so I don't know what design you referring at!

Big light cruiser.

You mean Design X? If you checked the post I've included the original official document which included the Hiraga drawing as well showing clearly where the magazines are located compared to the turrets.

Oh!!! My mistake - earlier, when I was studying the Hiragi archive, I did not come across this sketch, only the calculations. And now the links were not loading due to bad internet. After your post, I waited for it to load. Da Hiraga was an amazing designer. Very interesting version of "white elephants"!