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IJN post Taiho fleet carrier plans

ceccherini

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Taiho was ordered as part of Maru 4 fleet expansion program. She was a compromised design, mating an armored flight deck to a Shokaku size hull, resulting in lower freeboard an reduced hangar capacity. The first, prewar, draft of the subsequent Maru 5 plan included 3 more armored carriers of a different and larger design, called G14. The final wartime Maru 5 plan had provisions for 5 fleet carriers of a slightly enlarged and improved Taiho type, called G15 whose construction was never started because of the critical shortage of steel and manpower in wartime Japan. I was searching data of the secretive G14 project only to find a displacement of about 50000 ton, making it basically the Japanese equivalent of USN Midway class and planned RN Malta class. Also I find some scan from a Japanese magazine that seems to (I don't read japanese) report a length of 300 meters and a width of 35 meters and mention of two different proposal: one for a kind of super Taiho, the other for a flush deck carrier intended to be equipped with twin engine attack aircraft. I am honestly totally incapable to judge the credibility of this magazine and I would like your help.
 

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what is the magazine in question?
 

Tzoli

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There was also the G-18 design which looks like by the data an improved or modified Ibuki:
208x22m 56km/h, 80.000shp 2 shafts, 15.500/18.500tons, 2x2 76mm, 24x3 25mm AA, around 42 aircraft from 1944.

My info on the Japanese Midway or Shinano sized carrier was indeed 50.000tons standard and an aircraft complement of 84 planes from 1942/43
Also in the hull numbers list of the IJN 2 numbers were associated for this design: Hull numbers 801 and 802
 

JFC Fuller

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Does anyone have a full list of the ships planned under the pre-war draft MARU-5 programme?
 

ceccherini

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Does anyone have a full list of the ships planned under the pre-war draft MARU-5 programme?
One improved Yamato class battleship, 2 A-150 class battleships, 3 G14 class carriers, 2 B65 class battlecruiser, 5 light cruisers of a much improved Agano class variant (8 main guns, 38 knots of speed), 4 AA cruisers, 16 Akizuki class DD, 16 super Shimakaze class DD, 45 submarine and a large number of auxiliary ships for a total of 159 new ships and a total tonnage of about 650000 tons (that seems a bit low given the number and the size of the ships in the plan). There was also in preliminary study an even more ambitious maru 6 plan to complement Maru 5 that envisioned 4 A150/super A150 class battleships, 4 B65 Battlecruisers and 8 heavy cruisers of a new type
 
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Tzoli

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No, only two G-14 was ordered at least hull numbers associated with.
This is the list for the Maru 5 programme:

1 x Yamato Battleship (No. 797)
2 x A-150 “Super Yamato” Battleships (No 798 and No. 799)
2 x Type A Battlecruisers (Nos 795 to 796)
1 x Unryu Aircraft Carrier (No. 800)
2 x Kai-Taiho (G-14) Aircraft Carriers (No 801 and No 802)
1 x 11,000 ton Seaplane Tender (No. 809)
1 x Kai-Wakataka Netlayer (No. 819)
1 x Irako Supply Tanker (No. 845)
5 x Kai-Agano (C-44) Type B Cruisers (Nos 810 to 814)
1 x 6,800 ton Icebreaker (No. 846)
1 x Tsukushi Survey Ship (No. 847)
1 x Hashidate Gunboat (No. 867)
1 x I-400 Class Submarine (No. 714)
2 x I-9 Cruiser Submarines (Type A) (No. 700 and No. 701)
8 x I-15 Cruiser Submarines (Type B) (Nos. 702 to 709)
4 x I-46 Submarines (Nos. 710 to 713)
3 x I-351 Submarines (Nos. 730 to 732)
9 x RO-35 Submarines (Nos. 715 to 723)
10 x I-176 Submarines (Unknown Numbers)
9 x RO-100 Submarines (Unknown Numbers)
16 x Kai-Shimakaze Destroyers (No. 733 to 748)
16 x Kai-Akitsuki Destroyers (No. 770 to 785)
4 x Shumushu Escorts (Type A) (No. 790 to 793)
6 x 3,300 ton Seaplane Tenders (No. 803 to 808)
4 x Shokatu Escort Cruisers (No 815 to 818)
10 x No.19 Minesweepers (No. 820 to 829)
2 x Akashi Repair Ships (No. 840 and No. 841)
3 x Improved Kazahaya Supply Tankers (No. 842 to 844)
8 x Ajiro Minelayers (No. 850 to 857)
2 x Modified Nisshin Seaplane Carrier (No. 863 and No. 864)
2 x Modified Tsurugizaki Submarine Depot Ships (No. 865 and No. 866)
2 x Sumida Gunboats (No. 868 and No. 869)
9 x No.13 (CH-13) Subchasers (No. 870 to 878)
9 x 700 ton CH-60 Subchasers (No. 879 to 887)
2 x Tsugaru Minelayers
 

Flying Sorcerer

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No, only two G-14 was ordered at least hull numbers associated with.
This is the list for the Maru 5 programme:

1 x Yamato Battleship (No. 797)
2 x A-150 “Super Yamato” Battleships (No 798 and No. 799)
2 x Type A Battlecruisers (Nos 795 to 796)
1 x Unryu Aircraft Carrier (No. 800)
2 x Kai-Taiho (G-14) Aircraft Carriers (No 801 and No 802)
1 x 11,000 ton Seaplane Tender (No. 809)
1 x Kai-Wakataka Netlayer (No. 819)
1 x Irako Supply Tanker (No. 845)
5 x Kai-Agano (C-44) Type B Cruisers (Nos 810 to 814)
1 x 6,800 ton Icebreaker (No. 846)
1 x Tsukushi Survey Ship (No. 847)
1 x Hashidate Gunboat (No. 867)
1 x I-400 Class Submarine (No. 714)
2 x I-9 Cruiser Submarines (Type A) (No. 700 and No. 701)
8 x I-15 Cruiser Submarines (Type B) (Nos. 702 to 709)
4 x I-46 Submarines (Nos. 710 to 713)
3 x I-351 Submarines (Nos. 730 to 732)
9 x RO-35 Submarines (Nos. 715 to 723)
10 x I-176 Submarines (Unknown Numbers)
9 x RO-100 Submarines (Unknown Numbers)
16 x Kai-Shimakaze Destroyers (No. 733 to 748)
16 x Kai-Akitsuki Destroyers (No. 770 to 785)
4 x Shumushu Escorts (Type A) (No. 790 to 793)
6 x 3,300 ton Seaplane Tenders (No. 803 to 808)
4 x Shokatu Escort Cruisers (No 815 to 818)
10 x No.19 Minesweepers (No. 820 to 829)
2 x Akashi Repair Ships (No. 840 and No. 841)
3 x Improved Kazahaya Supply Tankers (No. 842 to 844)
8 x Ajiro Minelayers (No. 850 to 857)
2 x Modified Nisshin Seaplane Carrier (No. 863 and No. 864)
2 x Modified Tsurugizaki Submarine Depot Ships (No. 865 and No. 866)
2 x Sumida Gunboats (No. 868 and No. 869)
9 x No.13 (CH-13) Subchasers (No. 870 to 878)
9 x 700 ton CH-60 Subchasers (No. 879 to 887)
2 x Tsugaru Minelayers
Are there any good Enlgish-languages sources on this?
 

Tzoli

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Sadly many info about the IJN are only avaiable in Japanese and hence many info seems to not arrive in the western or in case USA eastern English speaking countries.
 

ceccherini

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No, only two G-14 was ordered at least hull numbers associated with.
This is the list for the Maru 5 programme:

1 x Yamato Battleship (No. 797)
2 x A-150 “Super Yamato” Battleships (No 798 and No. 799)
2 x Type A Battlecruisers (Nos 795 to 796)
1 x Unryu Aircraft Carrier (No. 800)
2 x Kai-Taiho (G-14) Aircraft Carriers (No 801 and No 802)
1 x 11,000 ton Seaplane Tender (No. 809)
1 x Kai-Wakataka Netlayer (No. 819)
1 x Irako Supply Tanker (No. 845)
5 x Kai-Agano (C-44) Type B Cruisers (Nos 810 to 814)
1 x 6,800 ton Icebreaker (No. 846)
1 x Tsukushi Survey Ship (No. 847)
1 x Hashidate Gunboat (No. 867)
1 x I-400 Class Submarine (No. 714)
2 x I-9 Cruiser Submarines (Type A) (No. 700 and No. 701)
8 x I-15 Cruiser Submarines (Type B) (Nos. 702 to 709)
4 x I-46 Submarines (Nos. 710 to 713)
3 x I-351 Submarines (Nos. 730 to 732)
9 x RO-35 Submarines (Nos. 715 to 723)
10 x I-176 Submarines (Unknown Numbers)
9 x RO-100 Submarines (Unknown Numbers)
16 x Kai-Shimakaze Destroyers (No. 733 to 748)
16 x Kai-Akitsuki Destroyers (No. 770 to 785)
4 x Shumushu Escorts (Type A) (No. 790 to 793)
6 x 3,300 ton Seaplane Tenders (No. 803 to 808)
4 x Shokatu Escort Cruisers (No 815 to 818)
10 x No.19 Minesweepers (No. 820 to 829)
2 x Akashi Repair Ships (No. 840 and No. 841)
3 x Improved Kazahaya Supply Tankers (No. 842 to 844)
8 x Ajiro Minelayers (No. 850 to 857)
2 x Modified Nisshin Seaplane Carrier (No. 863 and No. 864)
2 x Modified Tsurugizaki Submarine Depot Ships (No. 865 and No. 866)
2 x Sumida Gunboats (No. 868 and No. 869)
9 x No.13 (CH-13) Subchasers (No. 870 to 878)
9 x 700 ton CH-60 Subchasers (No. 879 to 887)
2 x Tsugaru Minelayers
Japanese Wikipedia page on Maru 5 report three stage of prewar planning regarding fleet carrier: at first three G14, then reduced to two while final, approved prewar Maru 5 comprised one G14 and two Unryu class "medium" carrier. Also at 50000 tons G14 is in no way a Tahio-kai, that were the G15 included in the wartime variant of Maru 5. This list lacks the somewhat misterious AA cruisers no.815-818 that were part of every iteration of prewar Maru 5
 

Tzoli

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It does mentions them just given them a name:
4 x Shokatu Escort Cruisers (No 815 to 818)
these hull numbers were associated to the AA cruisers.
Note these AA cruisers were not the 12x2 10cm armed Japanese Atlanta (Which was a project to finish the Oyodo then under construction) but rather an Agano sized Akizuki with 4x2 10cm, Depth Charges and 2x seaplanes
 

ceccherini

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It does mentions them just given them a name:
4 x Shokatu Escort Cruisers (No 815 to 818)
these hull numbers were associated to the AA cruisers.
Note these AA cruisers were not the 12x2 10cm armed Japanese Atlanta (Which was a project to finish the Oyodo then under construction) but rather an Agano sized Akizuki with 4x2 10c
m, Depth Charges and 2x seaplanes
You're right, I just didn't see it. If a remember correctly the project was for a leading of Akizuki class squadrons, so retain basic Akizuki capability with the addition of seaplane carrying capacity and flag staff space, something different not only in size and power but also in function from the often see Atlanta like project
 

JFC Fuller

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In terms of carriers that actually makes more sense - one G14 to form a carrier division with Taiho and then two new medium carriers to form another coherent division of lightly protected but fast carriers

Tzoli, you wrote on another form that the original plan was for 8 AA cruisers - one per Yamato, does this mean the Akizuki's were meant as escorts for the Yamatos with one destroyer squadron (with an AA cruiser as leader) per ship?
 

Tzoli

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To my knowledge the original Peace Goddess plan would mean a surface force centering around the Yamatos with a carrier squadron doing the pre-empitve strike on the enemy fleet and then the Yamatos would be sent for the final kill. AA defence would had been provided by the AA destroyers
 

blackkite

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Please show me the cover of this book.
Some translation.
大型航空母艦建造計画 構想と軌跡 : Large aircraft carrier consruction plan concept and trajectory
雲龍型(参考) Unryu type(reference)
改大鳳型 Modified Taiho type
大型空母案 : Large aircraft carrier plan
信濃 : Shinano
一一○号艦(参考) : No.110ship(reference)
山口多聞少将の新造空母案 : Newly construct aircraft carrier plan of Major General Tamon Yamaguchi(in 20th of February 1942)
最高速力 30ノット : Maximum speed 30knot
航続距離 18ノットで15000浬 : Range 1500nm speed 18knot
飛行甲板長 300米 : Flight deck length : 300m
幅35米 : Flight deck bredth : 35m
対空兵装 高角砲 20門 大型機銃 40門 : Anti aircraft weapon High angle cannon 20, Heavy gun 40
搭載艦戦(艦上戦闘機) 45 : carrier fighter on board 45
搭載艦爆(艦上爆撃機) 27 : Dive bomber on board 27
搭載艦攻(艦上攻撃機) 21 : carrier attack aircraft on board 21
重防御 : Heavy armar
 
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blackkite

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大型空母案(昭和15年 : 推定図)
特異な形状のエレベーターは双発艦攻(艦上攻撃機)を運用するためである。操艦用の艦橋を昇降式として設置することんも考えられていた。

Large Aircraft Carrier Proposal (Showa 15(1940) : Estimation) The elevator of a unique shape is to operate the twin-engine ship attack aircraft. It was also thought that the bridge for ship maneuvering to be installed as a lifting form.
 

ceccherini

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Stunning informations, thank you so much! So we can argue that G14 started in 1940 as a kind of super Tahio and then admiral Yamaguchi proposed to modify it in a flush deck carrier, I suppose a paper plan suggested by the early war experiences of an operative.
 

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It is interesting to speculate that MARU-6 could have included another pair of G14s to create another armoured carrier division - the growth in the weight of Japanese carrier aircraft would certainly have driven them to bigger ships and there were no shortage of dubious carriers in the Japanese fleet that would have needed replacing at some point. MARU-6 was apparently to have included another Yamato derivative (A150?) which would have allowed for the formation of two complete 4 ship Sentais by about 1950. Thats in addition to the various cruisers proposed.
 

blackkite

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What a detailed and difficult discussion!
 

ceccherini

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Interesting the speed of 30 knots, quite low by Japanese carriers standard. Maybe this is an indication that it was intended to adopt the standard Shokaku /Tahio 160000 hp plant also in this new class. Or maybe the quite low speed combined with the apparent lack of funnels and great range is an indication that for the modified 1942 version a diesel plant was proposed: the very same year seaplane carrier Nishin was completed with the first completely successful Japanese large diesel power plant. I read IJN was so satisfied with it that diesels were by then considered viable for future large surface ship, that because of war and defeat never came.
 

Tzoli

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Maybe that aircraft type should be asked in the aircrafts part of this forum
 

Tzoli

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Did somebody able to identify the aircraft or translate the text associated with the carrier proposal?
 

Julio Garay Terrazas

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¿Taiho Kai? Maybe I get all these information in the last century but i dont remember where and have to retouch the color image for a better view of the details.


NEVER BUILT 'NEXT' - TAIHO CLASS CARRIERS

By Noriki Suzuki

IJN carriers were very successful in the early stages of the war but were defeated in June 1942 at Midway, when four carriers were lost. So serious was the loss that the IJN modified its wartime supply plan 'Maru-Go' (Circle Five) to 'Kai-Maru-Go' (Revised Circle Five), intending to reinforce its air strike capability. The "Next-TAIHO class carriers" were a part of that plan. TAIHO was the only carrier included in 'Maru-Yon' (Circle Four) shipbuilding plan, featuring heavy armor, quite untypical for traditional IJN carriers.

The 'Next-TAIHO' class carrier was to be a larger, advanced version of TAIHO. TAIHO's displacement was 34,200 tons (trials); 'Next-TAIHO' was to be 35,800 tons and 4 meters longer. TAIHO's flight deck length was 257.5 meters and 'Next-TAIHO' 261.5 meters. TAIHO had six 100mm twin AA guns Type 98; 'Next-TAIHO' was designed to have eight Type 98s as suggested by TAIHO gun crews.

Another improvement was the revised anti-torpedo protection. Recognizing the development of enemy torpedo power, 'Next-TAIHO' had a well-designed under-water protection structure, enough to withstand a 350kg torpedo explosion. Again learning from Midway the electrically powered bucket chain hoists for bombs and torpedoes, connected flight deck and magazine directly. According to Revised Circle Five plan, the 'Next-TAIHO' was designed under basic design G-15.

The plan was to build five of these ships, numbered 5021 to 5025 at the following shipyards:

No.5021 at Kure Navy Yard

No.5022 at Kawasaki Kobe Yard//

No.5023 at Mitsubishi Nagasaki Yard//

No.5024 at Yokosuka Navy Yard

No.5025 at Kure Navy Yard.

However, the war situation prohibited building such high-quality giant flattops that needed too much tooling. Mass-produced medium carriers, with lesser attack capability but needing less building work were required. Therefore IJN authorities decided to build the UNRYU class prior to 'next-TAIHO' according to the same Revised Circle Five plan. UNRYU's design was based on HIRYU but featured some improvements. With the worsening war situation, the shortage of materials prevented any ship keel lay and abandoned their building.
 

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Thos9

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Were catapults intended for any projected carriers? What kind?
 

ceccherini

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Were catapults intended for any projected carriers? What kind?
It is known that Taiho was originally intended to be equipped with deck mounted catapults but during fitting out a RATO launching method for heavier plane was preferred. I suppose that during wartime they simply didn't have resources to be spared on new and not strictly necessary equipment and so they abandoned deck catapult development. I've never read anything about the characteristics of the planned catapult but it's most probably they were to be of the compressed air type, the only mature catapult tech of the day.
 

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Thank you.

About that time, the Germans had perfected the slotted-cylinder steam catapult for launching the V1 flying bomb though the steam source was high-test peroxide, not a boiler. Eventually the Japanese might have picked up that technology.
 

Tzoli

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Kaga was equipped with 2 experimental catapults during her modernization in 1934/35 but later removed as they were not successful (One was longer the other was slightly angled inwards if I remember the photos correcty.
Another 3 was installed briefly or intended to be installed in 1940 but not used or were not succeseful.
 

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There was also the G-18 design which looks like by the data an improved or modified Ibuki:
208x22m 56km/h, 80.000shp 2 shafts, 15.500/18.500tons, 2x2 76mm, 24x3 25mm AA, around 42 aircraft from 1944.

My info on the Japanese Midway or Shinano sized carrier was indeed 50.000tons standard and an aircraft complement of 84 planes from 1942/43
Also in the hull numbers list of the IJN 2 numbers were associated for this design: Hull numbers 801 and 802
There must be a G19 project of aTaiho successor any information or drawings about this stillborn carrier project?
 

Tzoli

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I doubt there was a G-19, as G-17 (Shinano) and G-18 were pretty late war already. Of course we don't know if they drawn up different plans at the end of the war!
 

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I doubt there was a G-19, as G-17 (Shinano) and G-18 were pretty late war already. Of course we don't know if they drawn up different plans at the end of the war!
I read in a naval book I don't know the title anymore, and they talked about a G19 project. It was indeed planned in the late 40 ties
 

Tzoli

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I've tried searching for
基本計画番号 - Kihon Keikaku Bangō - Basic Plan Numbers G19 or G-19
and
航空母艦 -Kōkū Bokan - Aircraft Carrier G19 or G-19
And did not found any mention so far
 

Tzoli

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No, hull number 802 was to be the second ship of the Japanese Midway:

Ship Numbers:
3 - Shokaku - Shokaku class aircraft carrier no.1
4 - Zuikaku - Shokaku class aircraft carrier no.2

130 - Taiho - Taiho class aircraft carrier no.1

302 - Unryu - Unryu class aircraft carrier no.1

801 - Design G-14 class aircraft carrier no.1
802 - Design G-14 class aircraft carrier no.2

5001 - Amagi - Unryu class aircraft carrier no.2
5002 - Unryu class aircraft carrier no.3
5003 - Katsuragi - Unryu class aircraft carrier no.4
5004 - Kasagi - Unryu class aircraft carrier no.5
5005 - Unryu class aircraft carrier no.6
5006 - Aso - Unryu class aircraft carrier no.7
5007 - Ikoma - Ikoma class aircraft carrier no.1
5008 - Kurama - Ikoma class aircraft carrier no.2
5009 - Ikoma class aircraft carrier no.3
5010 - Ikoma class aircraft carrier no.4
5011 - Ikoma class aircraft carrier no.5
5012 - Ikoma class aircraft carrier no.6
5013 - Ikoma class aircraft carrier no.7
5014 - Ikoma class aircraft carrier no.8
5015 - Ikoma class aircraft carrier no.9

5021 - Taiho Kai class aircraft carrier no.1
5022 - Taiho Kai class aircraft carrier no.2
5023 - Taiho Kai class aircraft carrier no.3
5024 - Taiho Kai class aircraft carrier no.4
5025 - Taiho Kai class aircraft carrier no.5
 

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Warships of The Imperial Japanese Navy (page 54) report Job no.801 and no.802 like first two carriers of improved Taiho followed by no. 5021 to no.5025 like G.15 design .
 
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