An alternate history of Japanese carrier development.

[Naval Aviation Fan]

So, before I get to posting anything about alternative IJN carrier development, I need to check my facts on what actually was done, for right now, with one exception, here is an image I created to help get needed info in one place.

As near as I could extract from the mess that is Wiki, this is what the IJN had for carriers in commission at the time of dec 7th, 1941 attack on PH. The exception is the carrier Ryuho, because I got very frustrated getting her confused with the earlier Ryujo.

Good carriers I listed in green, and sub-par carriers I listed in red.

I'm currently thinking about a threadmark post for each carrier, and with an eye for the changes getting handled likewise, to make them fit in more seamlessly with the OTL carrier construction. The goal is to move the thread along, carrier by carrier, using the threadmark feature, so folks can find the revelavent section of the thread's discussion. At this point, I'll ask for timing ideas for this from the community, as I don't want to spend too much time on any one carrier, but I do want folks to have a chance to be able to weigh in on each carrier, so, what do folks think about posting a new carrier each sunday?

The focus of this thread is to try to provide a detailed listing of each historical carrier built, and then introduce the ATL carriers when they would be built (and why), so we don't get things out of order, and folks can see at a glance what the current state of the IJN carrier force is with each threadmark post. As there are 10 carriers in the image from history, and I'm going to be adding in three to that, we should get a 13 week discussion that way.

What do you folks think?

 

[Naval Aviation Fan]

Chronologically speaking, the IJN had 3 ships that would become aircraft carriers laid down in 1920, the Kaga in July, followed by both Akagi and Hosho in Dec. Because only the IJN Hosho was designed to be a carrier right from the start, her construction moved forward rapidly, and although there were delays due to changes in her design, she went from laid down to commissioned in 2 years and 11 days.

Akagi commissioned Mar 1927
Kaga commissioned Nov 1929

Looking at this, the IJN had just one carrier in service from Q1, 1923 to Q1, 1927, and didn't historically get a third flight deck until Q4 1929.

Looking at the dates ships were laid down...

1920. Initial 3 ships laid down.
1929. First new carrier laid down Q4.
1933. First conversion ship laid down Q2.
1934. Second new carrier and second conversion ship laid down Q4.
1935. Third conversion ship laid down Q2.*
1936. Third new carrier laid down Q3.
1937. Fourth new carrier laid down Q4.
1938. Fifth new carrier laid down Q2.

This is telling, as the IJN didn't lay down a new carrier for 9 years, and then didn't even lay down a ship for later conversion until 4 years after that.

Another take is that,
1st carrier took 2 years and 11 days. 7,470t/15 aircraft/25 kts. In service Q4, 1922.
2nd carrier took 3 years, 5 months, and 13 days, and was a disaster waiting to happen as built, and needed a great amount of work. 10,600t/48 ac/29 kts. In service Q2, 1933.
3rd carrier took 3 years, 1 month, and 9 days. 16,200t/63 ac/34 kts. In service Q4, 1937.
4th carrier took 3 years, minus 3 days. 17,600t/64 ac/34 kts. In service Q3, 1939.
5th carrier took 3 years, 8 months, minus 4 days. 25,675t/72 ac/34+ kts. In service Q3, 1941.
6th carrier took 3 years, 4 months, and zero days. 29,800t/72 ac/34+ Kts. In service Q3, 1941.

All the prewar IJN fleet carriers took less than 4 years from laid down to being placed in commission, while the conversion ships typically took much longer.

 

[Naval Aviation Fan]

If one week seems to work, we could see Shoho posted on the 30th, followed by Akagi on the 7th, and Kaga on the 14th, and this would then bring us to the POD, where the New carriers would be introduced.

I had been thinking to just leave all follow on carriers the same (save for Ryujo of course) as that will make things far easier, but let me know what you all think.

 

[mack8]

Honestly can't say i really understand what you are after, but as IJN carriers are one of my favourite subjects, i do have various ideas of how they could fare/be better. While at the same time not provoking a US reaction that would cancel any IJN CV improvements.

Since we are starting with Hosho, here are a few of my ideas:

Hosho- How about making it bigger from the start say at 12,000-12,500 tons like it's projected 1921 follow on (called Shokaku, not to be confused with the 1937 Shokaku). I think some project sketches called for 30kts. Speed is always good, and it could carry more planes which would be helpful in WW2. Perhaps it could be reconstructed/modernized to some extent interwar like OTL Kaga and Akagi were.

Akagi class - How about somehow saving it's sister ship Amagi in the 1923 earthquake, so it is converted to a CV as initially planned, instead of Kaga. So you have a homogenous division with 31kts ships.

Ryujo - Absolutely, definitely must be built as a proper fleet CV, i imagine it as a sort of pre-Soryu, 15,000-16,000 tons, 32 kts, 70 planes capacity, they must lie and cheat through their teeth about it's displacement if they have to, just like they did OTL with Soryu and Hiryu. Preferably get a 70% ratio in CVs either at WNT or LNT which means 40,500 tons remaining instead of 27,000 after Akagi and Kaga (or Amagi TTL) are converted , so either they don't have to lie as much if they build 3 CV of 13,500 tons official displacement, or they build four 10,000 tons CVs official displacement (in reality they will be 16,-17,000 tons if they lie/cheat properly). Even a slower 28kts alt-Ryujo but of larger size similar to Ranger (14,000 tons or so) would still be more useful if it carries a larger number of planes- preferably as many as the OTL Soryu, but even as many as OTL Junyo would still be a welcome improvement.

Hiryu/Soryu- Add a bit more protection/stonger built if possible, say 17,000 tons for Soryu and 18,000 tons Hiryu.

If they have 70% ratio in CVs then under the WNT treaty limits they will neatly equal the USN, Langley vs alt-Hosho, 2 Akagi vs 2 Lexington, 2 Soryu vs 2 Yorktown and 2 alt-Ryujo vs Ranger/Wasp. If still 60% ratio at least the 14,000-16,000 ton alt-Ryujo will equal or surpass Ranger, Wasp being countered by the later Shokaku/Zuikaku.

Shokaku class- Fine as they are, perhaps slight improvements here or there if possible.

Junyo/Hiyo- Build them as proper carriers from the start, depending on slipway size either one Shokaku and one Hiryu, or 2 Shokakus, or even just 2 Hiryus, which are far better ships than the OTL Junyos.

I'll get to the CVL/CVE/MAC conversions next time.

 

[lionhead]

This is a nice chart i found some time ago to help:

although obviously imcomplete but i was never able to find the second part. I got them for US, German, and UK ship building too.

Addendum: Don't ask me what the colours mean though. No idea.

 

[mack8]

Oh that's fantastic, i've been loking for those for ages as i can't find them on my PC anymore! If you can post the US, German and UK ones somewhere or here would be awesome.

PS: At a cursory look it's missing no. 111 ( fourth Yamato) at Kure, also as i understand Shinano was built in it's own newly built drydock, not on the same one as Shokaku.
PPS: Missing also Junyo and Hiyo
PPPS: Also missing Zuikaku, Zuiho, Shoho, Ryuho, Chitose, Chiyoda, Nisshin, Mizuho, Ibuki of the top of my head, Kaga rebuilding too

It still has great potential if altered though.

 

[mack8]

Perhaps the above graph can be used in conjunction with this one:

 

[Naval Aviation Fan]

This is a nice chart i found some time ago to help:

View attachment 827405

although obviously imcomplete but i was never able to find the second part. I got them for US, German, and UK ship building too.

Addendum: Don't ask me what the colours mean though. No idea.

Awesome, just what I needed, making a new one specific to this thread as we speak.

 

[Naval Aviation Fan]

Ideas to make this better looking?

I like being able to show just how long the Kaga took to commission, in relation to the other pair of carriers started around the same time. That being said, I feel that a better job can be done.

 

[Naval Aviation Fan]

TL/DR

Not quite what I'm looking for in this thread.

Looking to discuss one carrier a week.
Each Sunday, the carrier talked about in the course of the week, gets a threadmark post, and we move on too the newer ships.
Keeping all three of the initial 1920 carriers as is. This doesn't get us the best IJN carrier force possible, but it does help me to learn how to write a thread like this.
New carriers will come in on week #4.

So until Sunday, we should concentrate on just the IJN Hosho, with the understanding that nothing will change from historical for the first three ships, but by week #4, we will be free to discuss the first new notional ship, and all that we could want that ship to be, when it should be built, and and everything related to the 4th Japanese aircraft carrier (instead of Ryuho), and this is where the fun can really begin.

The reason I want to approach this topic this way, is so that we have the historically limited IJN, and can see the improvements that make sense.

For instance, I find it kinda crazy the Japanese didn't lay down a new purpose built carrier until Q4 of 1929, especially seeing as how long the two big conversions took to commission.

 

[Naval Aviation Fan]

Looking at the image in post #9, it seems clear that the Japanese needed a 2nd aircraft carrier started before Akagi is placed in commission, but when should such a Hosho 2.0 be started, when would it be commissioned, and how different from Hosho should it be?

I should be clear, I'm angling for the IJN to build 4 carriers under the 10,000t limit of the WNT, Including the original Hosho, so any such carriers will not count towards the Japanese fleets total tonnage allocation, between 1923 and 1929. Mind you, I aim for all four such carriers to be in commission before Q1 1930, and preferably sooner.

If the Japanese want to build an exact copy of the Hosho (god knows why they would want to do that), then if they laid such a ship down Q1 1923, then I would expect them to be able to place it into commission by Q2 1925 (if not sooner) as they won't be needing to change it's design, and so can avoid the delays Hosho experienced.

This is the fastest way I can see for the IJN to get a second flattop into service. Anything bigger or more complicated is going to take longer. If they can avoid going all Ryujo and cramming way to much on it, it probably has less problems, gets built and commissioned faster than OTL Ryujo did, and turns out to be a better carrier overall.

Keep in mind, this notional carrier is NOT going to be designed to exploit the loophole, but is just a fortunate accident of design, keeping the investment down, as the ship will not be getting any design ideas from operational use of Hosho, as she herself just entered commission in Q1 1923.

Basically, I'm wanting the IJN to quickly build a second flattop, of limited capabilities (like Hosho) to increase their ability to pit carrier vs carrier training missions asap, and then, after a couple years of this experience, they lay down a 2 ship class, that gets to take into account the lessons learned. I would see these final two (light) carriers as being something less ham-fisted than Ryujo, and not getting infected by the need for doubling up the aircraft carried capacity.

I hope this clarifies what this thread is for/all about.

Have fun.

 

[jsb]

I got them for US, German, and UK ship building too.

Would be cool to see them all?

Looking at the image in post #9, it seems clear that the Japanese needed a 2nd aircraft carrier started before Akagi is placed in commission, but when should such a Hosho 2.0 be started, when would it be commissioned, and how different from Hosho should it be?

I should be clear, I'm angling for the IJN to build 4 carriers under the 10,000t limit of the WNT, Including the original Hosho, so any such carriers will not count towards the Japanese fleets total tonnage allocation, between 1923 and 1929. Mind you, I aim for all four such carriers to be in commission before Q1 1930, and preferably sooner.

If the Japanese want to build an exact copy of the Hosho (god knows why they would want to do that), then if they laid such a ship down Q1 1923, then I would expect them to be able to place it into commission by Q2 1925 (if not sooner) as they won't be needing to change it's design, and so can avoid the delays Hosho experienced.

This is the fastest way I can see for the IJN to get a second flattop into service. Anything bigger or more complicated is going to take longer. If they can avoid going all Ryujo and cramming way to much on it, it probably has less problems, gets built and commissioned faster than OTL Ryujo did, and turns out to be a better carrier overall.

Keep in mind, this notional carrier is NOT going to be designed to exploit the loophole, but is just a fortunate accident of design, keeping the investment down, as the ship will not be getting any design ideas from operational use of Hosho, as she herself just entered commission in Q1 1923.

Basically, I'm wanting the IJN to quickly build a second flattop, of limited capabilities (like Hosho) to increase their ability to pit carrier vs carrier training missions asap, and then, after a couple years of this experience, they lay down a 2 ship class, that gets to take into account the lessons learned. I would see these final two (light) carriers as being something less ham-fisted than Ryujo, and not getting infected by the need for doubling up the aircraft carried capacity.

I hope this clarifies what this thread is for/all about.

I just question if you can really say Hosho or any other nation's 1st gen CV are sub-par, you will always need to learn the first time and nobody will build large without hindsight for want is not a BV but a CV...hint in C not B it's not considered a capital ship yet....?

Also, the quake has maybe reduced IJN budgets a bit to build much in the gap and WNT reduced need etc.....

 

[jlckansas]

The big problem with the Japanese carrier's is the 1923 Kanto Earthquake. If you get the Amagi instead of the Kaga then you have a better start to the process without the compromises that they had to make with using the Kaga, a BB hull, instead of the Amagi, a BC hull. You have a better linear development with them having the two large, same class "Amagi", one small "Hosho", and one leftover "Ryujo" much like the U.S. With the comparison with the Kage to Akagi is the fact that they had the plans to rebuild the Akagi into a CV from BC but had no plans to rebuild the Kaga from a BB to CV and had to come up with those from scratch. You had an actual pause with the Kaga because it was orginally scheduled to be scrapped under the Washington Naval treaty.

 

[mack8]

Indeed the 1923 Kanto earthquake had a terrible effect on the IJN (and Japan as a whole). It destroyed Amagi and Naka (which was started again in 1924) on the slips, severe shipyard damage etc. This caused the 1923 program to be delayed in completion, and presumably that's why the 1927 program was only half the size.

Btw regarding Hosho and subsequent carriers, the two 12,500 tond enlarged Hoshos ( Shokaku class) were planned under the 8-8 program, however after the WNT was signed they were cancelled (alongside with the BB/BCs and a lot of other ships), and funds were instead directed to convert Akagi and Kaga under the newly put together 1923 program. Japanese wiki pages on japanese whipbuilding programs are a real treasure trove of info.

大正12年度艦艇補充計画 - Wikipedia

ja.wikipedia.org

 

[Naval Aviation Fan]

I just question if you can really say Hosho or any other nation's 1st gen CV are sub-par, you will always need to learn the first time.

While I would agree, this would need me not to look at Hosho with hindsight. I'm sure the folks that built her thought she was good enough in the time frame in question.

and nobody will build large without hindsight for want is not a BV but a CV...hint in C not B it's not considered a capital ship yet....?

Yep, I'm taking that into account. My plan is to talk about the three initial IJN carriers, noting their strengths and weaknesses, and then introduce the idea of Japan building more <10,000 ton ships. earlier than Ryujo, precisely because they don't know what they want/need from a carrier, and so they build small/cheap ships to be able to gain better understanding of just what a carrier arm is (or could eventually grow into), and cheap, and earlier is the way to go in my opinion.

On that note, let me ask a question:
Would the IJN be better served by a quick (just under two years) construction of a notional Hosho 2.0, as close to an exact match to the first ship, so that there would not be any discrepancy in the ships capabilities, or would building a bit bigger (than Hosho's 7,470 tons, but still less than 10,000 tons), and a ships that would likely have a larger airgroup, and probably faster, as well?

For myself, I initially scoffed at the idea of proposing a repeat of the Hosho, as any new ship would almost certainly be a faster ship, and carry more aircraft, at the cost of a longer build time, but then I thought about the benefits or a pair of matched carriers, working together and gaining expertise.

So, would you propose a quick repeat of the 7,470 ton Hosho, or something like a 9,470 ton ship with 30 aircraft and a speed of 30 knots?

Also, the quake has maybe reduced IJN budgets a bit to build much in the gap and WNT reduced need etc.....

Well, if the cost of a few small ships, built between 1923-1930 is going to bankrupt the IJN, we could just call it good and leave it at that, lol.

The big problem with the Japanese carrier's is the 1923 Kanto Earthquake.

Indeed the 1923 Kanto earthquake had a terrible effect on the IJN (and Japan as a whole). It destroyed Amagi and Naka (which was started again in 1924) on the slips, severe shipyard damage etc. This caused the 1923 program to be delayed in completion, and presumably that's why the 1927 program was only half the size.

I had no idea that that earthquake was that bad.

That being said, if we are going to talk atl carriers, we are going to need to build them.

I'm basically looking to have the IJN build three more light (<10,000t) carriers, and then let the cards drop where they may, can we move forward with that, or just end the thread?

 

[lionhead]

Oh that's fantastic, i've been loking for those for ages as i can't find them on my PC anymore! If you can post the US, German and UK ones somewhere or here would be awesome.

PS: At a cursory look it's missing no. 111 ( fourth Yamato) at Kure, also as i understand Shinano was built in it's own newly built drydock, not on the same one as Shokaku.
PPS: Missing also Junyo and Hiyo
PPPS: Also missing Zuikaku, Zuiho, Shoho, Ryuho, Chitose, Chiyoda, Nisshin, Mizuho, Ibuki of the top of my head, Kaga rebuilding too

It still has great potential if altered though.

Would be cool to see them all?

Well only if the OP @Naval Aviation Fan doesn't mind. If not I can PM them of course.

Like i said the Japanese one is incomplete as it misses several ships build at shipyards depicted(Zuikaku was build at Kawasaki as well) and ends before 1944. The ones i have for US, UK and Germany are complete though as far as i know.

 

[Naval Aviation Fan]

Well only if the OP @Naval Aviation Fan doesn't mind. If not I can PM them of course.

Like i said the Japanese one is incomplete as it misses several ships build at shipyards depicted(Zuikaku was build at Kawasaki as well) and ends before 1944. The ones i have for US, UK and Germany are complete though as far as i know.

go for it

 

[lionhead]

go for it

well alright then @mack8 @jsb

first the german one, not that interesting tbh.

next the 2 US ones

and finally the 2 UK

French, Italian, Russian, Dutch. no clue if there are more. I don't even know who made them unfortunately.

colour coding seems lot more clear on these though, they represent the different ship types.

 

[mack8]

Fantastic, thanks a lot Lionhead. I also have a different set for US shipbuilding that also includes slip length, but it only starts from 1940. Fortunately that one i had it printed long ago in case i lost it, which i did, i know it's on my comp somewher but where among some tens or hundreds of GBs worth of stuff hell knows. And i think yet a different one for IJN shipbuilding than above, but couldn't find the blimmin' thing if my life depends on it either.

 

[Dorknought]

In terms of the first 3 carriers, not much can be done with Hosho. She is a good first try giving enough experience early on. From here I'd simply make the decision on the need for 3 or 4 carriers under the WNT tonnage of 81000tons over the 20 year expected life of carriers. If converting Akagi and Amagi for 26,000tons each then that leaves 29,000 tons. I can't build 1 carrier of that tonnage so will go for 2 14,500ton carriers. Once Amagi is wrecked then I'd shift to 1 26,000ton (Akagi) and 3 18,333ton new builds skipping the Kaga conversion. Use the design and operational experience of Hosho and Akagi to design the first 18,000 ton carrier built in place of Ruyjo in 1928 not 1929.