Question about IJN Shinano Air Group.

[Werner]

She was hauling suicide boats and rockets from Yokosuka to Kure.

she had been launched around 45 days earlier.

[chuck]

If one were to pursue the question of where the height of Japanese carrier development would have led, it is clear one should start the exploration with the Taiho, and not the Shinano. And although Taiho is not without her flaws, overall she was a very good design that managed to combine the best of armored defensive carrier philosophy with the best of unarmored offensive carrier philosophy. One should use the Taiho as starting point for exploring where Japanese carrier design might have led, not Shinano.

I suspect the Japanese really would have been better off if Shinano had been allowed to be completed in her intended battleship form than in her half-assed carrier form.

[Lesforan]

Well, the problem with converting a carrier from something else is you always have baggage from the "something else" to deal with.

It seems to me that the most successful conversions were those based on battlecruisers, although the Kaga conversion was reasonable successful. The British, Americans, and Japanese had battlecruisers to convert under the Washington Treaty.
These yielded fast carriers, although they had to deal with relatively narrow hulls. Battleship to carrier conversions always seemed to involve weight problems: excessive hull armor, or the need to compensate for the weight lost when the big turrets were removed.

I don't think another Yamato-class battleship would have helped the Japanese. By refusing to committ these ships until late in the war, the Japanese assured their destruction. Maybe if all four were completed and used together as a surface battle group they could have achieved something beyond being floating office buildings for the IJN staff.

[chuck]

Yamato hull was really too slow to have made a good basis for carrier conversion. Besides that, the main problem was Shinano hull was too far advanced to be converted efficiently and directly to a carrier hull, and the Japanese didn't have the time to go back and rework major portions of the hull for carrier duty. To make Yamato hull into an efficient carrier, almost every interior structure down to the waterline would have to be razed and rebuilt. This was done with Akagi and Kaga But Akagi conversion took 5 years, and Kaga took a similar amount of time. To make a Yamato hull into a slow but efficient carrier would have required a comparable amount of work.

The weight of the turrets originally intended for the ship was in and of itself not a problem. That lost top weight can easily be compensated by a couple of additional inches of flight deck armor.

[bengtsson]

The USN went with the ESSEX design as their top second half Carrier. Wouldn't the Japanese been much better off just going with an improved Shokaku class. I mean once the 2 Shokakus were in the water beginning slightly improved version on the same building ways. Getting an improved Shokaku would be roughly equivalant to the Essex. In a war, you don;t always have time for "one of" experimental ships. You need proven designs in number.
In the context of war against the USN, weren't Taiho and Shinano slowing down a standard carrier design all purpose fleet carrier? I admire the Taiho design, a fine ship, but not what I'de have time for in a world war situation. The USN picked a design and stayed with it. Japan might have got more fleet carrier bang for the buck with a standard improved Shokaku.

Bob B.

[Werner]

Japan's "mass production" carrier was a slightly modified Hiryu -- the Unryu (or Amagi) type.

Shokaku was probably their best design, but Unryu offered mass production benefits. It used either standard cruiser or destroyer machinery, and importantly, was shorter and lighter, which permitted it to be handled in a much larger subset of Japanese facilities. Like the UK, Japan had a severe limitation in length and beam for ships to be accommodated in places other than the yards specifically modified in 1938-40 to handle the Yamato class.

[chuck]

Shukaku was really contemporary with the Yorktown class, and the two classes were closely comparable in both statistics and in what their battle records reflected. The Japanese contemporary of the Essex was really the Taiho. However, after Yorktown/Shukaku, US went for a linear development of the Yorktown, and Japanese turn some degrees away from their previous direction, so Essex and Taiho didn't look as close to each other as Shukaku had to the Yorktown. But Taiho really was the Japanese equivalent of the Essex. Every new generation carrier aircraft the Japanese had in development in 1941 was too large to be used effectively on Amagi/Uruyu class, and were designed for operation from a carrier with elevator, hanger and deck size of a Taiho. Had the war not occurred, it was clear that some version of Taiho design was going to be the mainstay of the Japanese carrier force. Amagi class was an emergency measure instituted after the war had started. It was not part of the original Japanese carrier development road map.

[Werner]

... except the Japanese could not afford to build Taiho in numbers, although they ordered "Improved Taiho"s, none appear to have been started. Unryu was ordered in numbers, with a half-dozen actually in process.

[chuck]

With no trade, fuel or raw material embargoes, the Japanese industrial base (8 -10 million tons of steel annually) could sustain the pace of an annual balanced building program involving perhaps 2 Taihos for many years. keep in mind that such a pace was already far greater than the pace of new construction seen under the Washington/London treaty regimes. When Taiho and Essex classes were being developed, the Japanese probably assumed that a balanced construction program that involves 2-3 new carriers a year was going to be the on-going pace of the pacific arms race on both sides. The Japanese had a low opinion of American willingness to trade butter for guns. So from the perspective of 1938 or 1939, it would not have been ridiculous for the Japanese to assume that they could keep pace both qualitatively and quantitatively with Taiho design.

Amagi design was really a post midway emergency program. The pre-war Japanese naval build up had always been undertaken mainly to maintain a fleet so difficult and expensive to eventually defeat that the US would sooner come to an accommodation with Japan than attempt to defeat it inside the timeframe of 1940-1955. Only secondarily was the fleet also intended to defeat USN's first major blow should the war come. The idea presumably was that, with 15 years of peaceful development and uninterrupted exploitation of the Chinese and Korean colonies, Japanese industrial and economic might would grow to such an extend as to allow Japan to take care of itself without bluster after 1955.

Accepting qualitative inferiority in return for numerical parity was not the Japanese style. There is just no way one could imagine a fleet of 19,000 ton Amagi carriers could field the sort of aircraft that would go on intimidating the US fleet, equipped as it would be with far larger carriers, out to the time frame of 1950 or 1955. So there is no way Amagi's could have formed any pre-war Japanese carrier development roadmap.

[Dan K]

Excellent synopsis of IJN CV development by Chuck, and Werner. Incidentally, Richard Wolfe (he of the long running AOTS Taiho project) has some done some sophisticated computer modeling of Taiho and is of the opinion that she is an outgrowth of the Hiryu design, not Shokaku. FWIW.

Shinano's construction had already been halted by Pearl Harbor by Adm. Yamamoto. In view of European events (Taranto, Bismarck), the already dwindling state of raw material and rising demand for competing wartime construction, it was recognized that another Yamato type BB was not going to add much to the IJN equation. The problem was what to do with her. Despite the obvious alternative value of her building materials, scrapping her was projected to take an inordinately long time. She sat dormant in that Yokosuka drydock until after Midway, when her completion as a CV was really taken as a matter of expediancy to replace lost flight decks.

In retrospect, she should have been scrapped immediately. Any of the existing CV designs could have been easily replicated in the 3 three year time frame (pre-Pearl Harbor stoppage to final completion) with the alternative use of the same material. Actually, multiple CVs could have been built from the same material within the same timeframe, IMHO.

[MartinJQuinn]

So how far along was Shinano when work was stopped? Did she already resemble a battleship? Was any of her superstructure or barbettes in place?

[chuck]

In June 1941, when worked stopped, Shinano was about 18 month away from completion as a battleship. Based on analogy with Yamato's construction, I would say the hull was just past the launch stage, which means it is structurally complete, machinery, barbette and deck armor would be in place, and weather deck essentially sealed. Some superstructure work would soon start, and preparation would be underway to begin assembling the main turrets inside the barbettes.

[MartinJQuinn]

In June 1941, when worked stopped, Shinano was about 18 month away from completion as a battleship. Based on analogy with Yamato's construction, I would say the hull was just past the launch stage, which means it is structurally complete, machinery, barbette and deck armor would be in place, and weather deck essentially sealed. Some superstructure work would soon start, and preparation would be underway to begin assembling the main turrets inside the barbettes.

Thanks Chuck - I never realize she was that close to being finished.

[chuck]

In retrospect, she should have been scrapped immediately. Any of the existing CV designs could have been easily replicated in the 3 three year time frame (pre-Pearl Harbor stoppage to final completion) with the alternative use of the same material. Actually, multiple CVs could have been built from the same material within the same timeframe, IMHO.

Given the dire emergency created by Midway and the fact that the Japanese were not planning to essentially loosing the war during the time it would take to convert the Shinano, I think the decision to convert her was understandable. I doubt scrapping her immediately upon the decision to stop her construction would have greatly improved the situation. Scrapping her starting in late 1941 would mean the bulk of her material would not be available for any new construction until early 1943. So any carrier born of her material would not become available until 1946.

In reality, her construction as a battleship was stopped at the worst possible time. Her own construction and the parallel construction of her guns, armor and equipment would have already consumed almost all of the material she was ever to need. Little material savings can be gained by stopping at that time. She was almost ready for launch, but not quite, so stopping her construction at that time means she would sit idle, continuing to occupy an absolutely invaluable large dry dock for no good reason, for another year. Compare to her total cost up to this time, the additional cost associated with finishing her would be relatively minor. As she was fitting out, she would occupy a comparatively much less valuable fitting out basin. I think by June 1941, the Japanese really should have just let her be completed.

[Dan K]

Agree that much of her material will take time to be be reworked but my thinking was that the very availability of additional material made it fungible. Other material could be drawn upon while her's was removed/melted down/recast, used elsewhere.