Japanese defeat at Midway on 4-6 June 1942 brought very painful understanding of the importance of the Kido Butai - Carrier Task Force. So Japanese Navy very quickly created a plan to rebuild it, adopting new carrier strength expansion plan on 30 June 1942.
According
to the plan, main strength of the new Kido Butai were to compose improved
versions of already existing designs: 5 large carriers of the “Taiho” class
(with armored flying deck) and 13 medium carriers of the “Unryu” class. To together
with original “Taiho” and “Unryu”, that were already building, it provided for
20 carriers = 3 heavy and 7 medium carrier divisions.
For details
see attached table 7.5 from the book “Japanese Cruisers of the Pacific War” by
Lacroix and Wells (with some of my clarifications added):
The problem
was – building large warship is neither fast nor easy. As a result main
strength of the plan to be completed only in 1947(!). So IJN had to improvise,
doing quick conversion of other ships in order at least to regain pre-war
carrier force strength before new carriers will enter service. 6 ships were
chosen for conversion plus 3 more were added later. Other battleships and heavy
cruisers were considered, but eventually ideas of their conversion were
abandoned due to the need of those ships as they were.
As you can
see, according to the above table IJN can’t even achieve December 1941 level of
aircraft strength aboard fleet carriers (that is, excluding 4 slow CVs: “Shinyo”
and “Taiyo” class) before mid-1944. And IJN expected the number of US fleet aircraft
carriers (CVs, CVLs) will be 12 by the end of 1943 (compare with 7 CVs in
December 1941).
So the
question of “quick and dirty” increase of carrier strength till 1945 at least was
of paramount importance for the IJN. There is little use of new carriers if the
fleet is already defeated. As it happened in real life in 1944. Of course, lack
of carrier capacity is definitely not the only reason for Japanese defeats, yet
it’s one of the obscure ones, usually limited to the usual explanations of
Japan’s industry problems. But industry did its best: “Taiho” and first 3 “Unryus”
were completed before planned dates. Yet it was still too late, as only “Taiho “was
able to take part in Philippine Sea Battle against US carrier task force in
June 1944.
That’s why
the first two years of IJN carrier strength expansion plan of June 1942 worth more
careful study. Could IJN do better
there, than in the original plan?
All 1942 FY
ships of the plan are pre-Midway plans and little extra could be done here (to
be precise “Chuyo” orders to start conversion were issued after Midway battle
(on 21 June 1942), but planning for conversion was obviously done before the battle).
Among 1943
FY ships initially there were only two warships: “Chitose” and “Chiyoda”. They
were both built as seaplane carriers (CVS) with construction allowing for conversion
into carrier. So they were to be converted into CVLs which can carry some 30
planes each. Looks good – until we find out, that at the same time IJN
desperately tried to attend lack of seaplane capacity of the fleet. Cruiser “Mogami”
and oiler “Hayasui” received expanded seaplane facilities. Later on “Ise” class
battleships and “Tamano” class oilers were also to receive capability to carry seaplanes
and even launch carrier aircraft from special trollies. All this added no
carrier decks, but at the same time relieved carriers from such tasks as reconnaissance,
anti-submarine patrols, etc. And new seaplane fighters and dive-bombers allowed
for support of the regular carriers in combat. Each plane, doing such job from
the board of the CVS, relieved a plane aboard CV for other mission.
Now the mystery:
why to convert existing seaplane carriers into regular carriers if you still need
seaplane carriers??? In mid-1942 there were 3 high-speed CVS in the IJN:
“Chitose”, “Chiyoda” and “Nisshin” (last two were converted into midget
submarine carriers, but still could carry seaplanes on the upper decks).
Instead of quick re-conversion of two ships into CVS, “Chitose” and “Chiyoda”
were converted into carriers while “Nisshin” remained to be used as fast transport
without any plans for its CV conversion. In my opinion, “Chitose”, “Chiyoda”
and “Nisshin” with some 20 seaplanes each would’ve been way better addition to
the fleet, then converted “Mogami”, “Ise” and “Hyuga”. And the conversion times
will be way shorter.
Now about
other ships in this plan: “Kaiyo” (ex-“Argentina Maru”) and “Brazil Maru”.
Together with other 4 CVs, converted from merchant ships, they are often called
“escort carriers” – which is incorrect. Those 2 ships were to receive destroyer
turbines so they could operate with “Junyo” class CVs and older battleships.
But this never happened. Just like planned conversion of 3 ships of the “Asama
Maru” class along the same lines. Some other ships can follow, each carrying
c.20 planes. Of course, those ships weren’t as good, as purpose-built carriers.
But they were there and could bring up IJN fleet carrier strength by 100-plus
aircraft by mid-1944.
Another mystery
is lack of progress with aircraft carrying fast oilers of “Hayasui” and “Tamano”
classes, also ordered in 1942. Of 15 ships planned only “Hayasui” was
completed. They were too complicated for mass production? – Why not to build
something similar on the base of standard 1TL wartime standard tankers?
But the
biggest mystery of them all in this 1942 plan is a total lack of anything resembling
carriers, built on the hulls of wartime standard ships. After Midway there was
a special study about merchantmen, converted into carriers to transport
aircraft. Even if they had little value for the fleet battle, they can relieve
fleet carriers from transport missions, convoy escort and other secondary
duties. But only in 1944 few such ships were planned, but even then at first as
Merchant aircraft carriers, which continued to carry cargo and operated under
civilian command with small military aircraft detachment aboard. Only later some
of them become full-fledged escort carriers. The most surprising – the driving
force behind this was apparently not Japanese Navy, but Japanese Army.
One can say
all those change doesn’t matter. IJN was doomed to lose from the beginning of
the war due to the disparity of strength with its enemies. May be. But it doesn’t
mean we shouldn’t research the decisions made by the Japanese Navy to see if
they were optimal or not.
Eugen Pinak
23 October 2022
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