Why is everything that the Japanese did after June 1942 seen as a kneejerk reaction to the outcome of MIdway? Some of it was but some of it went way back in IJN planning in case of just such an event.
There are two strands to the story:-
1. Subsidisation of merchant ship construction from the late 1920s of vessels considered suitable for conversion to carriers in the event of war.
Asama Maru class (3 ships completed 1929/30) - all lost before conversion could be carried out
Nitta Maru class (3 ships ordered 1937) - bacame the CVE Taiyo, Unyo & Shinyo
Argentina Maru class (2 ships ordered 1938) - name ship became CVE Kaiyo with second lost before conversion could occur.
Kashiwara Maru class (2 ships ordered 1938/39) - became Hiyo & Junyo.
Hiyo & Junyo were acquired by the IJN in Oct 1940 (officially Feb 1941) while on the slip and completed as carriers in 1942.
As for the CVEs, Taiyo was converted in 1941, entering service in Sept that year. Unyo began conversion in Nov 1941 and completed in May 1942. Chuyo was converted between July & Nov 1942, so had clearly been planned prior to Midway. Kaiyo's conversion was between Dec 1942 & Nov 1943. Shinyo was the odd ship out as she was the German liner Scharnhorst trapped in Japan on the outbreak of WW2 and acquired by the IJN in spring 1942 with initial plans for use as a transport but the changed to a CVE. She followed Chuyo in the yard and was converted between Sept 1942 & Nov 1943.
So only the last 2 of these conversions can be seen as a reaction to Midway (see below).
2. Construction of various naval auxiliaries from the early 1930s that could be converted to carriers in the event of war.
2 Submarine support ships. Zuiho converted before completion and completed as a carrier in 1940. Shoho converted Jan-Nov 1941
1 Submarine support ship. Ryuho converted to a carrier Dec 1941-Nov 1942.
1 Seaplane carrier / midget sub carrier. MIzuho lost before conversion could occur.
2 Seaplane / midget sub carriers. Chitose & Chiyoda were ordered to be converted to carriers in Sept 1942 with actual conversion occurring Jan-Dec 1943.
So again only the last pair can be seen as a reaction to Midway. Chiyoda's conversion is supposed to have influenced the reconstruction of Shinano which took place in the same yard.
Japanes post Midway planning began on 20/21 June 1942 with a conference on the Yamato.
The conversion of Mogami came about because the IJN realised after Operation C & Midway that they had inadequate reconnaissance assets. Recce was the responsibility of seaplanes carried on the cruisers and in particular the Tone & Chikuma. The perceived need was for a single additional ship. As Mogami needed extensive reconstruction and had had one of her aft turrets destroyed anyway, she was selected for rebuild to fill the gap. Her repair & conversion only took 8 months between Sept 1942 & April 1943.
When it came to the Ise & Hyuga, these were a reaction to Midway with plans initially drawn up in Aug 1942. Initially the proposal was for a full carrier conversion. A battleship/carrier with only the 2 forward turrets, was then proposed. But the constraints then laid down were for retention of at least 3 turrets and completion in 1943. But the intended airgroup for these ships was originally to have been D4Y Susisei dive bombers, only later changing to a mix of E-16A Zuiun recce floatplanes and D4Y. After launch the surviving D4Y would have landed on other carriers or ashore. The entire rebuild project took from Oct 1942 to Nov 1943.
As for Ibuki, Hans Lengerer published an article in Warship 2017 about the ship and I also have Lacroix's Japanese Cruiser book in the library. She was only laid down on 24 April 1942. Post Midway, the original plan would have seen both Ibuki & a sister ship cancelled and broken up on the slip (Warship 301 laid down 1 June 1942 and construction was stopped 30 June 1942 with carrier 5001 laid down in its place in Oct 1942). According to Lacroix, Ibuki was also cancelled on 30 June but work was ordered restarted and accelerated on 30 July to clear the slip to allow a carrier to be laid down. She was launched in May 1943 and work on her was abandoned in July according to Lacroix. Lengerer notes "At the time of her launch the hull structure was almost complete to the upper deck". So it seems highly unlikely that any machinery or gun turrets had been installed as indicated in the Japanese Wiki article, especially given that there was no plan for the hull at that stage.
The Japanese Naval General Staff in July 1942 considered her completion as a heavy cruiser as meaningless according to Lengerer, and her hull was, at that stage, not considered adequate for conversion as a carrier to take the next generation of IJN aircraft then in development. After that various conversion proposals were made including seaplane tender / fast transport and fleet tanker before conversion to a light fleet carrier once again came to the fore. It was therefore Aug 1943 before a decision for the light carrier conversion was made, Oct 1943 before those new carrier plans were completed and Nov before the incomplete hull was towed from Kure to Sasebo for completion. Estimated completion was March 1945 but by then she was only 80% complete when work stopped altogether.
Ibuki was essentially a modified Suzuya (sub-class of the Mogami class). Those ships took 42-46 months to build. And that under peacetime conditions. In July 1941 the Japanese included her in a so called "Urgent Programme" for ships intended to complete by 1 April 1944. But that plan was not activated until Sept 1941 and she was not ordered until Nov 1941 and she was finally laid down in May 1942. So to me it seems impossible that she could have been completed by Spring 1944 even in modified form, given that almost a year had slipped between her inclusion in an "urgent" programme and actually being laid down, especially once the effects of the war started to bite.
Shinano was reportedly 70% complete by June 1942 per Combined Fleet site. The decision to convert her to a carrier was taken in July 1942. I'm not sure how that then matches a subsequent statement on the same site.
"16 July 1942:
The projected specifications for No.110's conversion are laid out. It is to be completed as an armored aircraft carrier, closely modeled after No.130 TAIHO. At the time No.110 had had its turbines and nine of its twelve boilers installed. The floor of the magazines of No.1 and No.3 turrets had been completed, and the bulkheads had risen as high as the Middle Deck level."
Her rebuild started in early 1943 but initially proceeded slowly.
As a battleship carrier she would have been just as useless as the Ise & Hyuga conversions. Every nation looked at combined battleship / carriers at some stage or other and Japan was the only one that progressed the idea. And that only because of her extreme situation. While completing Shinano in the way that you propose might have been technically possible it would have been an even bigger waste of resources that what was done to her historically.
There are two strands to the story:-
1. Subsidisation of merchant ship construction from the late 1920s of vessels considered suitable for conversion to carriers in the event of war.
Asama Maru class (3 ships completed 1929/30) - all lost before conversion could be carried out
Nitta Maru class (3 ships ordered 1937) - bacame the CVE Taiyo, Unyo & Shinyo
Argentina Maru class (2 ships ordered 1938) - name ship became CVE Kaiyo with second lost before conversion could occur.
Kashiwara Maru class (2 ships ordered 1938/39) - became Hiyo & Junyo.
Hiyo & Junyo were acquired by the IJN in Oct 1940 (officially Feb 1941) while on the slip and completed as carriers in 1942.
As for the CVEs, Taiyo was converted in 1941, entering service in Sept that year. Unyo began conversion in Nov 1941 and completed in May 1942. Chuyo was converted between July & Nov 1942, so had clearly been planned prior to Midway. Kaiyo's conversion was between Dec 1942 & Nov 1943. Shinyo was the odd ship out as she was the German liner Scharnhorst trapped in Japan on the outbreak of WW2 and acquired by the IJN in spring 1942 with initial plans for use as a transport but the changed to a CVE. She followed Chuyo in the yard and was converted between Sept 1942 & Nov 1943.
So only the last 2 of these conversions can be seen as a reaction to Midway (see below).
2. Construction of various naval auxiliaries from the early 1930s that could be converted to carriers in the event of war.
2 Submarine support ships. Zuiho converted before completion and completed as a carrier in 1940. Shoho converted Jan-Nov 1941
1 Submarine support ship. Ryuho converted to a carrier Dec 1941-Nov 1942.
1 Seaplane carrier / midget sub carrier. MIzuho lost before conversion could occur.
2 Seaplane / midget sub carriers. Chitose & Chiyoda were ordered to be converted to carriers in Sept 1942 with actual conversion occurring Jan-Dec 1943.
So again only the last pair can be seen as a reaction to Midway. Chiyoda's conversion is supposed to have influenced the reconstruction of Shinano which took place in the same yard.
Japanes post Midway planning began on 20/21 June 1942 with a conference on the Yamato.
The conversion of Mogami came about because the IJN realised after Operation C & Midway that they had inadequate reconnaissance assets. Recce was the responsibility of seaplanes carried on the cruisers and in particular the Tone & Chikuma. The perceived need was for a single additional ship. As Mogami needed extensive reconstruction and had had one of her aft turrets destroyed anyway, she was selected for rebuild to fill the gap. Her repair & conversion only took 8 months between Sept 1942 & April 1943.
When it came to the Ise & Hyuga, these were a reaction to Midway with plans initially drawn up in Aug 1942. Initially the proposal was for a full carrier conversion. A battleship/carrier with only the 2 forward turrets, was then proposed. But the constraints then laid down were for retention of at least 3 turrets and completion in 1943. But the intended airgroup for these ships was originally to have been D4Y Susisei dive bombers, only later changing to a mix of E-16A Zuiun recce floatplanes and D4Y. After launch the surviving D4Y would have landed on other carriers or ashore. The entire rebuild project took from Oct 1942 to Nov 1943.
As for Ibuki, Hans Lengerer published an article in Warship 2017 about the ship and I also have Lacroix's Japanese Cruiser book in the library. She was only laid down on 24 April 1942. Post Midway, the original plan would have seen both Ibuki & a sister ship cancelled and broken up on the slip (Warship 301 laid down 1 June 1942 and construction was stopped 30 June 1942 with carrier 5001 laid down in its place in Oct 1942). According to Lacroix, Ibuki was also cancelled on 30 June but work was ordered restarted and accelerated on 30 July to clear the slip to allow a carrier to be laid down. She was launched in May 1943 and work on her was abandoned in July according to Lacroix. Lengerer notes "At the time of her launch the hull structure was almost complete to the upper deck". So it seems highly unlikely that any machinery or gun turrets had been installed as indicated in the Japanese Wiki article, especially given that there was no plan for the hull at that stage.
The Japanese Naval General Staff in July 1942 considered her completion as a heavy cruiser as meaningless according to Lengerer, and her hull was, at that stage, not considered adequate for conversion as a carrier to take the next generation of IJN aircraft then in development. After that various conversion proposals were made including seaplane tender / fast transport and fleet tanker before conversion to a light fleet carrier once again came to the fore. It was therefore Aug 1943 before a decision for the light carrier conversion was made, Oct 1943 before those new carrier plans were completed and Nov before the incomplete hull was towed from Kure to Sasebo for completion. Estimated completion was March 1945 but by then she was only 80% complete when work stopped altogether.
Ibuki was essentially a modified Suzuya (sub-class of the Mogami class). Those ships took 42-46 months to build. And that under peacetime conditions. In July 1941 the Japanese included her in a so called "Urgent Programme" for ships intended to complete by 1 April 1944. But that plan was not activated until Sept 1941 and she was not ordered until Nov 1941 and she was finally laid down in May 1942. So to me it seems impossible that she could have been completed by Spring 1944 even in modified form, given that almost a year had slipped between her inclusion in an "urgent" programme and actually being laid down, especially once the effects of the war started to bite.
Shinano was reportedly 70% complete by June 1942 per Combined Fleet site. The decision to convert her to a carrier was taken in July 1942. I'm not sure how that then matches a subsequent statement on the same site.
"16 July 1942:
The projected specifications for No.110's conversion are laid out. It is to be completed as an armored aircraft carrier, closely modeled after No.130 TAIHO. At the time No.110 had had its turbines and nine of its twelve boilers installed. The floor of the magazines of No.1 and No.3 turrets had been completed, and the bulkheads had risen as high as the Middle Deck level."
Her rebuild started in early 1943 but initially proceeded slowly.
As a battleship carrier she would have been just as useless as the Ise & Hyuga conversions. Every nation looked at combined battleship / carriers at some stage or other and Japan was the only one that progressed the idea. And that only because of her extreme situation. While completing Shinano in the way that you propose might have been technically possible it would have been an even bigger waste of resources that what was done to her historically.
