What if Japan had diverted resources from Yamatos

[Ob1kinob]

What if Japan had diverted resources from Yamatos to fully embrace carrier warfare, i.e. More Shokaku class carriers available Dec 7th, subsequently able to do more complete job on Dec 7th, perhaps seek out Lexington and Enterprise during attack( who had no where to hide or replenish), also if they directed submarine resources to anti merchant shipping

[Kingfish]

You would end up with the same results

Case in point: by 1945 the US had commissioned 141 carriers of various sizes, Japan: 17.
The same disparity is evident in aircraft production - US 320K to Japan's 76K.

It also stands to reason that any deviation from the OTL would affect both sides. In other words, an expanded IJN carrier building program would be met in kind by an expanded US effort.

[maltesefalcon]

Traditional doctrine swung from capital ships to aircraft carriers based on the result of the Pearl Harbor raid. Before that it would be tough to convince the traditonalists in either navy that the sun had set on big gun naval strategy.

In fact many of the carriers extant were only there because of the limits on capital ships imposed by the Washington Naval Treaties. Existing large hulls could be converted into carriers instead of being scrapped to meet the treaty limits.

[Sheldrake]

The japanese would have needed more than carriers. They would have needed a lot more aircraft and a better established training programme.

Incidentally the Japanese only operated the forth largest carrier force. Royal Navy and the British Merchant Navy each operated more carriers than the IJN.

[Guaporense]

The japanese would have needed more than carriers. They would have needed a lot more aircraft and a better established training programme.

Japanese aircraft production was very high in WW2, at 75,000 machines. Relatively higher than their carrier output if compared to the US.

Incidentally the Japanese only operated the forth largest carrier force. Royal Navy and the British Merchant Navy each operated more carriers than the IJN.

Assuming that the UK wasn't a single country that is.

Overall, it was a gift to the Allies that Japan wasted their resources on the obsolete weapon that was the battleship, other countries did the same (Germany with their Bismark ships, US with their Iowas, etc).

[Guaporense]

You would end up with the same results

Case in point: by 1945 the US had commissioned 141 carriers of various sizes, Japan: 17.
The same disparity is evident in aircraft production - US 320K to Japan's 76K.

It also stands to reason that any deviation from the OTL would affect both sides. In other words, an expanded IJN carrier building program would be met in kind by an expanded US effort.

US resources were not infinite however, you have to find out were they could cut in order to make more carriers. Maybe the 4 Iowas but they were made years after the Yamatos.

[T. A. Gardner]

There are a number of issues here:

First, it isn't a simple tonnage construction issue. Japan's ability to produce turbines and machinery was limited too. So is yard space. They have only so many slips. So, if they get rid of the Yamato's that might give them 3 or 4 additional carriers in their place.

I could also see the IJN not converting everything in sight just prior to the war into carriers the way they did. All of their CVL were produced by converting existing ships per a pre-war plan. Here, that might not be the case. Those ships might be reserved for later conversion as necessary instead.
So, the most likely is they lay down two G8 projects (repeat Soryu class) getting these shortly before the war starts, and start the Unryu class (repeat Zuikaku) that start coming into service in late 1942. This would mean realistically, that Japan could have sustained their pre-war carrier fleet strength with war losses into late 1943 before being overwhelmed instead of by late 1942.

Then there's the problem of air crew and aircraft. Just 4 large carriers would mean some of them using A5M, D1A, with a shortage of B5N2. Their pilot and aircrew training programs were horribly slow and had very high washout rates.

Then there's the US response. Does the US know about this treaty violation? This would have pushed Japan well over the WNT carrier tonnage limits. But, let's assume they managed to keep it secret at least until the WNT lapsed.

In that case, the US starts building carriers like they did. But, needing additional ones quickly they pull in as many as a dozen large ocean liners under the XCV program (planned but never executed historically) and convert them to auxiliary carriers to be completed M+ 90 to M + 180 (days past mobilization or activation of the plan). These ships would carry in 1939 - 40 an air wing of 60 to 72 aircraft each.
All the conversion planning already existed. All the US had to do was get the ships in a yard and begin the conversion process.

But, once a war started between Japan and the US, Japan is finished in any case. The US built during the war 22 CV (21 Essex and 1 Midway) along with 6 CVL (Independence class) along with well over 100 CVE.

By mid to late 1943 Japan is doomed and the change does nothing to stop that.

[Kingfish]

US resources were not infinite however, you have to find out were they could cut in order to make more carriers. Maybe the 4 Iowas but they were made years after the Yamatos.

I wouldn't see it as much a "cut" as a redirect.

This WI presupposes a shift in IJN naval strategy towards a carrier centric fleet before the onset of hostilities, and given that the Yamatos were laid down almost 3 years before the Iowas it stands to reason the latter would not have reached the planning stage.

[T. A. Gardner]

I don't think the US would have changed their mobilization plans in any significant way. Maybe lay down additional Essex class earlier, but it is likely the Iowa class would still be built. These were designed in the late 30's and ordered and started in 1939 - 40 at a time when the USN didn't even know the Yamato class really existed or its specifications.

But, like I already pointed out, the Japanese are limited by yard space and things like machinery production. Let's say they lay down two G 8 designs (repeat Soryu class) such that these complete within a year of the war starting. They lay down two additional Zuikaku class that complete about the time the war starts. That would give Japan an advantage in large carriers initially.

But, on war production? The Japanese also completed four light carriers pre-war or early in the war that were started pre-war: Ryujo, Zuiho, Shoho, and Ryuho. None of these was considered particularly successful and their operations were usually relegated to secondary tasks and theaters.
Zuiho and Shoho also took about 3 1/2 years to be converted because of all sorts of issues that came up. As one example, their diesel machinery as sub tenders was replaced with destroyer turbines which were not really suited to carrier use.

They then completed two liner conversions off ex-German ocean liners stuck in Japan at the outbreak of the war: Junyo and Hiyo. Neither was considered fully successful.

The Taiho was a "reply" to the US Essex class, and a single ship built. There were plans to build 4 more (Kawasaki jobs 801 and 802, Mitsubishi 5021 and 5022) but these were never laid down.

Shinano wouldn't exist in this scenario.

The big "emergency" class was the Unryu's. These were repeat Hiryu / Soryu class carriers of about 17,000 tons or about 50% the standard displacement of the Essex class. Six were laid down. Three completed in 1944 - 45. Another 10 were planned but not started.

The seaplane tenders Chitose and Chiyoda were converted to carriers in 1943 but were pretty marginal light carriers with 30 planes each.

Japan also converted the light cruiser Ibuki but the ship wasn't completed by war's end.

Rounding things out there are a half dozen or so merchant conversions of dubious value.

So, the likely outcome of cancelling the Yamato class is Japan gets 2 carriers when the war commences they didn't have, 2 more shortly after it begins, and 2 more sometime in mid 42. They complete another 4 to 6 by 1945. In addition, they get an odd lot of 6 to 8 light carriers like they did historically by conversion, a couple of iffy liner conversions, and have a handful of CVE.

The US by mid 1943 has the first 6 or so Essex in service in addition to whatever pre-war carriers survive. By 1944 the number rises to close to 20 fleet carriers, a half dozen CVL, and as many as 100 CVE.

So, the US starts the war with 7 CV, then builds another 22. Japan in this scenario starts with 8 or 9 and builds 6 to 8 CV.
The US builds 6 CVL, Japan 6 or 7.
The US builds over 100 CVE, Japan 6 or so.

Nothing really changes. Japan loses, and loses bad.

[Takao]

Japanese aircraft production was very high in WW2, at 75,000 machines. Relatively higher than their carrier output if compared to the US.

Actually, it was about 10,000 aircraft lower, around 65,000. About some 7,500 aircraft were already on hand - which gives the higher figure.

Overall, it was a gift to the Allies that Japan wasted their resources on the obsolete weapon that was the battleship, other countries did the same (Germany with their Bismark ships, US with their Iowas, etc).

It was hardly a "gift", and the Japanese lack of fuel, their focus on fighting one decisive battle, and the relative weakness of Japanese AA capabilities prevented the Japanese from using their battleships effectively.


Sheldrake brings up a good point. The Japanese capacity to train new pilots to man the air groups of the new aircraft carriers, as well as, replacing expected losses.

It is worth noting that the recently commissioned Shokaku and Zuikaku torpedo squadrons were manned by pilots considered inferior, and as such, were relegated to level-bombing for the attack on Pearl Harbor. Not to mention that the IJNAF was also undergoing a massive expansion of squadrons, and was lacking in trained pilots to man these new squadrons.

So, while the Japanese might get 2 more aircraft carriers prior to Pearl Harbor...How effective will they be with relatively untrained pilots? Even after several months, the Japanese aviators of the Shokaku and Zuikaku fared rather poorly at Coral Sea.

[Takao]

The US by mid 1943 has the first 6 or so Essex in service in addition to whatever pre-war carriers survive. By 1944 the number rises to close to 20 fleet carriers, a half dozen CVL, and as many as 100 CVE.

So, the US starts the war with 7 CV, then builds another 22. Japan in this scenario starts with 8 or 9 and builds 6 to 8 CV.
The US builds 6 CVL, Japan 6 or 7.
The US builds over 100 CVE, Japan 6 or so.

Nothing really changes. Japan loses, and loses bad.

Worth mentioning that the US cancelled some 8 Essex class & 3 Midway class carriers as the war was winding down. This would make the United States even more formidable carrier opponent should the war drag on.

[Guaporense]

Japan didn't plan to fight battles with carriers but to fight defensively so that US would need carriers to attack the islands Japan had occupied while Japanese forces would take-off from these islands. The problem was the lack of training for the additional pilots.

Well, the main problem with Japan was the fact that their strategy presupposed to Germany won in Europe. With the failure of Operation Blue in 42-43, Japan's fate was sealed with Germany's and there was nothing that they could do about it. Being more efficient, such as not wasting money on Yamatos, would increase American losses but the US was determined to fight it to the end and overall US losses against Japan were historically light.

Their strategy also presupposed that the US wouldn't be willing to suffer as many casualties as they actually did: they wanted to defend their territories and assumed that the US would give up after suffering some tens of thousands of casualties. They didn't expect the US to mobilize for total war in the way they did as well.

Also, they were really unlucky in Midway. Losing 4 carriers to the US's loss of 1 was really inefficient specially given that Japan had numerical superiority in the pacific (they were the ones who should have been inflicting disproportionate casualties).

[Guaporense]

So, the US starts the war with 7 CV, then builds another 22. Japan in this scenario starts with 8 or 9 and builds 6 to 8 CV.

Nothing really changes. Japan loses, and loses bad.

Well, if Japan were historically more efficient, suppose that it's a war only between fleet carriers and suppose Japanese fleet is 50% more effective in inflicting losses than the US was. Suppose US production of carriers is 3 times larger.

Then suppose Japan starts with 9 carriers and US starts with 7 and each Japanese carrier inflicts .6 losses per period while each US carrier inflicts .4 losses per period, then Japan inflicts 5-6 losses to the US while US inflicts only 3 losses to Japan, next period Japan has 6 carriers and builds another 2, the US starts with 1-2 carriers and builds another 6. The odds are 8 to 7-8. So eventually the Japanese would collapse but they would inflict very heavy losses on the US before that.

Historically they failed to be more effective even when they had numerical superiority. Had Japan been effective they could have inflicted much more serious losses which would have made the war less one sided. In 1944, for instance, Japan build 19,000 combat aircraft, the US build 74,000 but most of these were dedicated to Europe, only about 25,000-30,000 were used in the Pacific, yet the Japanese couldn't inflict substantial losses on US aircraft.

[T. A. Gardner]

Oh, so now suddenly the Japanese are also "more effective." Even if Japan has 9 large carriers to the US's 7, it really changes nothing. The US could choose to act more cautiously and defensively in the Pacific until they built up strength. In carrier on carrier battles early on the losses were about 1 to 1, Midway being something of a fluke.

But, even with that, the Japanese face rapidly increasing USN effectiveness while their own forces are pretty much are static in terms of tactics and technology.
One particularly effective USN development was the pre-war introduction of carrier controlled intercept (CCI). The USN began practicing directing CAP from their carriers using fighter controllers and radar, taking a page out of British tactics doing this. CAP went from 4 to 8 planes at Coral Sea to as many as 30+ by Midway. Japanese strike losses grew from 5 to 10% initially to 50 to 75% by Midway almost entirely because of this now entrenched and refined system.

The Japanese had nothing comparable. They put up CAP and the pilots were expected to spot enemy aircraft on their own and engage them. They lacked radar, and many fighter planes lacked radios, often removed by the pilots who felt their unreliability made them useless extra weight. So, the Japanese CAP typically engaged USN strikes at 10 to 20 miles from their carriers, at most. This gave them just a few minutes to work a strike over before it arrived on target.
The USN by Midway was engaging at 40 to 60 miles out and that increased as fighter direction moved to cruisers then destroyers. By Okinawa engagement was at over 100 miles. It pretty much ensured any Japanese strike would be decimated. It also ensured that virtually 100% of Japanese strikes got engaged.

So, even with more carriers, the losses in aircraft alone will pretty much do in the IJNAF just as it did historically.

The same goes for shipboard AA fire. The Japanese had really bad AA systems on their ships. Their destroyers had dual purpose 5" for the most part by 1941, but these reloaded at a fixed elevation so the ROF was 6 to 10 rounds a minute with low accuracy. Most larger classes had 8 4.7" or 5" guns in twin mounts with rudimentary director control. They used the 25mm Hotchkiss twin and triple mounts for light AA using nothing more than ring sights. The mounts were not powered.
Then they used the horribly ineffective 3 Sanshikhi (I probably spelled that wrong) shell that was in essence a shrapnel round using incendiaries. It put out a colorful, but useless, fireworks display.
Japanese doctrine also called for AA gunners to hold fire until aircraft were relatively close to improve their chance of hitting. This just makes it more likely that the attacking aircraft will succeed in hitting the ship.
Compounding those problems, the IJN had nothing in doctrine to improve defense against aircraft. Ships maneuvered independently to defend themselves against aircraft and steaming formations were line ahead and column of divisions unchanged from WW 1.

The USN had developed the circular formation and dispersed carriers within these formations. These gave mutual support and let the escorting ships coordinate their AA fire with the capital ships. It meant the attackers got far more attention and time undergoing AA fire resulting in more shot down or damaged. Their AA systems were superior too.

So, it is a virtual certainty that the IJNAF would be hit so hard by late 1942 that they'd need a year or more to replace their losses, making what carriers they still had all but ineffective. That happened historically too.
Worse, much of the IJN's strength would also be pulled away to operate from land bases in defense of atolls and such or for offensive operations in lieu of carriers. The same thing will occur.

The whole Japanese plan was based on wishful thinking. Had they been realistic about forming a defense of Pacific islands and atolls they might well have made the whole US endeavor too expensive to easily defeat them. But, that wasn't to be.

[Takao]

Historically they failed to be more effective even when they had numerical superiority. Had Japan been effective they could have inflicted much more serious losses which would have made the war less one sided. In 1944, for instance, Japan build 19,000 combat aircraft, the US build 74,000 but most of these were dedicated to Europe, only about 25,000-30,000 were used in the Pacific, yet the Japanese couldn't inflict substantial losses on US aircraft.

25,000 is about right only pertaining to USN carrier aircraft(25,236). Now, you add in the USN land-based aircraft - 20,624. Then you add in the USAAF combat aircraft in the Pacific, Far East Air Force, and the CBI - 4,767.

For a grand total of 50,627 US combat aircraft facing the 19,000 Japanese new construction...

Now, where is this "numerical superiority" you speak of?