No Yamato's?

As for an extra one or two carriers compared to OTL, getting pilots of them is again relatively easy, the IJNAF had i think about 4000 pilots in 1941, mostly for their shore based units. Have enough of them retrained to fill one or two extra carriers, sure, this might butterfly a handful of landbased fighter and bomber/attack units, but nothing impossible or improbable.

To clarify this part further as i was in a hurry few hours ago, probably this is a more convoluted way, since we know 3 basic facts, one, the japanese were rejecting a lot of potentially good candidates in their prewar training only keeping the very best, two, during the war however they found enough pilots to man their 50,000 plus combat aircraft they produced (just that they didn't had time and later in the war fuel to train them well), and three the requirements in fuel to train one extra airgroup are minuscule compared to total consumption in prewar years, obviously the simplest way is to just train the one extra carrier air group from scratch starting 1937 when our POD occurs, all else being equal.

About the extra BB and CV, the potential bottleneck would be machinery, there is not a lot of data about that part around, but again, there is a relatively simple way to get around that, just fit the two Hiryus with 104,000HP destroyer machinery like they did later in the war, and power the Shokaku and the 3 BBs with 160,000HP machinery (replacing the OTL 150,000HP Yamato machinery). Having couple of destroyers delayed won't be that big of a deal compared to the overall benefits of this ATL program being implemented.

PS: Oh and regarding getting these extra BB and CV, IF the above chart is accurate in this respect, to get the Hiryu CV yes you can replace Nisshin (and perhaps replace Junyo with the other Hiryu, a tight fit but they could probably just about have it ready for Pearl Harbour, if not shortly thereafter) while to get the extra 40-45,000 ton Yamato, since the slipway requirements for such a ship would not be as demanding as for the OTL Yamato, perhaps just some relatively straighforward deepening work for the docks where the OTL Shokaku or Zuikaku were built would be enough to get it laid down in 1938 there. Can also take the Mizuho out of this ATL building program to ease things up.
 
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Another sensible and therefore ASB use of the resources would be to build as many fast tankers as possible with the resources. I wrote fast tankers because they could make more trips and they would be harder to sink.

The American Cimarron class oilers had a standard displacement of 7,256 tons and boilers producing 13,500 SHP driving 2 shafts for a maximum speed of 18.3 knots.

It's a crude calculation but in terms of steel one Yamato equals 10 fast tankers and in terms of horsepower one Yamato equals 11 fast tankers. THEREFORE 30 fast tankers could theoretically have been built instead of Yamato, Musashi and Shinano.

IOTL 4 Cimarron class oilers were completed as the Sangamon class escort carriers and the design was also the basis of the Commencent Bay class escort carriers. Therefore what might happen is that the 20 ships laid down instead of Yamato and Musashi are completed as tankers while the 10 ships laid down instead of Shinano are completed as escort carriers. But before anybody replies I admit its an ASB idea because its too sensible.
 
Another sensible and therefore ASB use of the resources would be to build as many fast tankers as possible with the resources. ....

It's a crude calculation but in terms of steel one Yamato equals 10 fast tankers and in terms of horsepower one Yamato equals 11 fast tankers. THEREFORE 30 fast tankers could theoretically have been built instead of Yamato, Musashi and Shinano.

......

Depending on how its counted Japan started the Pacific war in 1941 with only 60 tankers. That probably includes coasters, yard hulks for storage, inland sea barges, & antiques. Modern blue water tankers were closer to 40, so adding 30 more in 1941-42 is big in terms of oil delivery. Still it does not win the war.
 
Depending on how its counted Japan started the Pacific war in 1941 with only 60 tankers. That probably includes coasters, yard hulks for storage, inland sea barges, & antiques. Modern blue water tankers were closer to 40, so adding 30 more in 1941-42 is big in terms of oil delivery. Still it does not win the war.
I thought it would be roughly, 20 coming into service between 1940 and the end of 1942 instead of the Yamato and Musashi. The other 10 would follow over 1943-44 and might be completed as escort carriers, possibly instead of the liners converted to aircraft carriers from 1942.

On that subject the Japanese Government might also have been better off subsidizing the construction of 6 fast tankers capable of conversion into aircraft carriers instead of the liners that were completed as Hiyo and Junyo. The Japanese Ministry of Transport (or its equivalent) might decide that reducing the country's dependence on foreign tankers was more important than subsidizing a pair of super liners. For the IJN the advantage might be that although the aircraft carrier versions were several knots slower they did not have the hangar height restrictions that Hiyo and Junyo had plus six ships carrying 27 aircraft each is a total of 162 against Hiyo and Junyo's combined capacity of 108 aircraft.

I agree that it doesn't alter the result of the war, but was there anything Japan could do to win the war? Correcting all the avoidable mistakes they made only prolongs the agony for both sides.
 
to have an efficient carrier force, IJN must change their training doctrine. Once your fighter pilot ( or dive bomber or torpedo bomber) is a veteran, get him back to the rear and transform him into an instructor. In the long run, you avoid having rookies getting butchered by experienced US and RN pilots, at least partially. Second, improve the AA capacities of the fleet which in OTL were a sad joke. the 25 mm gun was an utter disaster. So replace him, get some medium AA gun ( the 40 mm bofors is the best or the 37 mm german one once it become full automatic) and create AA cruisers. Three, Hiryu and Shokaku are fine, but at least protect their fuel tankers, otherwise, big boom in one hit.
 
I thought it would be roughly, 20 coming into service between 1940 and the end of 1942 instead of the Yamato and Musashi. The other 10 would follow over 1943-44 and might be completed as escort carriers, possibly instead of the liners converted to aircraft carriers from 1942.

Even another twenty in 1941 is very helpful

On that subject the Japanese Government might also have been better off subsidizing the construction of 6 fast tankers

There was a emergency construction program started. I can't recall exactly how many tankers were built 1941-44, but have seen claims more were sunk than afloat in Dec 1941.
 
The British official history on the War Against Japan says the Japanese only had 575,000 tons of tankers at the outbreak of war. When I was looking it up I found this paragraph, which I thought was worth copying.
Events were to provide that her calculations were based on false premises. Japan began the war with a tanker fleet of only some 575,000 tons, for she had allowed the bulk of her large pre-war imports of oil to be carried in foreign bottoms. Her new construction in 1942 and 1943 was considerably greater than losses, and by November 1943 the tanker tonnage had reached 834,000, but this was insufficient since three quarters of it was employed solely on the task of moving oil from the Southern Region to Japan, and the remainder was used to supply the forces holding the conquered territories in the Pacific and in the south. The United States had in the meanwhile begun a long-distance blockade by launching a submarine offensive aimed at the destruction of shipping and in particular tankers. Owing to the distance of the Americans bases from the vital sea route between the Southern Region and Japan, sinkings in 1942 and 1943 were not sufficient to reduce Japanese tanker tonnage, which reached its peak in November-December 1943. As the American offensive in the Pacific gained momentum and the chain of Japanese island defences was steadily pushed back westwards, not only could American submarines work closer to the China coast, with a consequent increase in the number of tankers sunk, but the fast carrier force was also able to strike at the Japanese forward naval bases. In 2 such strikes on Truk and Palau in February and March 1944, the fast carrier force sank a third of the tankers attached to the Combined Fleet, a loss that affected all subsequent fleet movements. When the greater part of New Guinea had been occupied by the end of July 1944 and the Marinas had been captured by August, the weight of attack on the Japanese lifeline greatly increased, and the tonnage of shipping sunk, including tankers, soared. The occupation of Leyte and Luzon between October 1944 and March 1945 cut the lifeline. Very few tankers managed to complete the voyage from the Southern Region to Japan in the first quarter of 1945, and the last tanker left the southern oilfields for Japan on the 19th March 1945.
However, the source does say that between 8th December 1941 and 15th August 1945 Japan lost 259 tankers of 1,284,956 tons, gross and that this only included ships of over 500 tons, gross as follows:

08/12/41 to 31/12/42 - 2 ships of 9,538 tons, gross
01/01/43 to 31/12/43 - 23 ships of 169,491 tons, gross
01/01/44 to 31/12/44 - 131 ships of 754,889 tons, gross
01/01/45 to 15/08/45 - 103 ships of 351,028 tons gross

Total 259 tankers of 1,284,946 tons, gross

Unfortunately it doesn't say how many tankers were built over the same period
 
Instead of building any type of battleship, Japan would have been better to use all that steel for building carriers and more escorts for convoys. But I doubt the battleship admirals would have allowed their sacred cows to be lost.
That's an argument that doesn't really work until the late thirties, prior till then carrier aircraft couldn't seriously threaten Battleships at sea, the technology of the day wasn't advanced enough. The aircraft bombs and torpedos were not powerful enough.
 
I've heard for years that IJN pilot training doctrine was antiquated and couldn't turn out replacement pilots fast enough. Can you elaborate on that?
the fleet air arm of the IJN was always seen as an elite corps, since the very beginning. With a very long and demanding training. In 1941, they had around 1500 very very good pilots. the first problem was they had 1500 pilots for 1500 machines. You lose the machine, you lose the pilot, doesn't serve to have a replacement machine since you have no replacement for the pilot. Second, the problem of the IJN was the same than the Luftwaffe, once you send a pilot into combat, he must fight to victory or death. He's not send to the rear ( except for permission). The wallies understood how precious a experienced pilot was so after a good number of combat missions, they were relieved to form new pilots, tell them their personal technics to fight etc. So the wallies hadn't a whole bunch of top-aces but a massive flow of good trained pilots during the whole war. A good pilot needs two years of training, and for aircraft carrier, it's even more demanding. So if you have 1500 superb pilots and lose 200 in corail see then 200 in Midway, your toy is utterly gutted.
 
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