1930's Japanese Navy - What would you have done differently?

[Garyt]

Just had a thought run through my head.

The Japanese "Decisive Battle" plan revolved around what they thought they had learned at Tsushima, along with updates as technology updated.

What they really failed to learn though is that the Victory at Tsushima had much to do with logistics - without the Russian Baltic fleet having to travel thousands of miles, the result may have been different.

But in failing to truly take into account the importance of logistics in winning a naval war the Japanese shot themselves in the foot for their efforts in WW2

 

[parsifal]

Issues about naval intell need to be put into perspective. The JN25 code was introduced just prior to PH and remained secure until the Tokyo raids in April. the flurry of signal traffic that followed that attack compromised the code, and the Japanese were very lax in not changing the code until AFTER Midway, by which time the Americans were reading about 80% of IJN traffic.

After Midway, new code books were finally issued and Japanese signal traffic returned to a level of security...sufficient to give them victory at Savo Island. The USN was again plunged into signal blindness. That remained the case until the end of the Guadacanal campaign. USN remained ignorant of Japanese evacuation.

The key to successful intell was not some magic bullet (please pardon the pun), but resources. throughout 1943 and 44 the allies poured more and more resources into the code breaking efforts. by the end of 1943, there were nearly 40000 codebreakers hard at work working continuously on breaking IJN codes. tens of thousands more were at work on the Army codes. Like the Germans in Europe there was no effective answer to that. There was absolutely nothing the IJN could have done to secure its signal security after 1943. before 1943, they should have focussed on the basics....that is, changing the codes more regularly.

With regard to radar, it was a conscious decision by the IJN not to pour money into radar technologies. The problem for them was again a question of resources. Whereas in 1944, it was quite common for US warships to carry at least one radar, down to PT boat size, and for DDs to be carrying four or five radars, the Japanese were struggling to fit even one radar to even major warships. moreover by the time they realized its importance, the IJN was a full generation behind the Allies in terms of technical proficiency. Radar fitouts on ships remained very rudimentary and unsatisfactory, and training in operation very poor. it was the same situation with ASDIC.

The Japanese needed to work on their ASDIC techs, their ASW training and they absolutely needed an airborne EW radar . The other gunnery and FC radars would have been noice to haver but not essential.

 

[cherry blossom]

Issues about naval intell need to be put into perspective. The JN25 code was introduced just prior to PH and remained secure until the Tokyo raids in April. the flurry of signal traffic that followed that attack compromised the code, and the Japanese were very lax in not changing the code until AFTER Midway, by which time the Americans were reading about 80% of IJN traffic.

After Midway, new code books were finally issued and Japanese signal traffic returned to a level of security...sufficient to give them victory at Savo Island. The USN was again plunged into signal blindness. That remained the case until the end of the Guadacanal campaign. USN remained ignorant of Japanese evacuation.

The key to successful intell was not some magic bullet (please pardon the pun), but resources. throughout 1943 and 44 the allies poured more and more resources into the code breaking efforts. by the end of 1943, there were nearly 40000 codebreakers hard at work working continuously on breaking IJN codes. tens of thousands more were at work on the Army codes. Like the Germans in Europe there was no effective answer to that. There was absolutely nothing the IJN could have done to secure its signal security after 1943. before 1943, they should have focussed on the basics....that is, changing the codes more regularly.

...snip....

I don't think that you have realized how stupid the IJN was with its codes. There is the issue of poor training. The additive tables of JN25B had 50,000 groups of numbers but 60% of the messages used the first 10,000 numbers as most clerks started on page 1 and as you mention they did not change the books often enough.

There is no sensible justification for having each code group divisible by three. If a transmission or decoding produced an error, there was only a one third chance that the erroneous group would be divisible by three. However, if the group cannot be found in the code book, it is clearly an error, and even with the divisibility by three, it is still not at all simple to guess what the correct group should be as any of the five numbers could be wrong. Clearly the IJN was reaching towards error checking codes but they were nowhere near getting that idea to work. They were, however, making their opponent's task much simpler. For example, occasionally the clerk would forget to add the superencipherment. Such signals were immediately identifiable as all the groups were divisible by three. The more mathematical consequences are explained in "The Flaw in the JN-25 Series of Ciphers, II" by Peter Donovan http://carma.newcastle.edu.au/jon/Preprints/Papers/Submitted Papers/Walks/Dirks notes/09duc1.pdf.

As we both agree, there was no way a simple superenciphered code such as JN-25 could have resisted the sort of effort used against it (and the slightly better RN codes also fell to the Germans). However, I believe that using conversion squares plus a grille with enciphered indicators would have resisted solution during WW2 with the same frequency of replacement of code books as OTL.

 

[cherry blossom]

Sorry about the no response, Cherry Blossum. That's what happens when you try to bring a thread back on track

I think we had sidetracked into "The accuracy of WW2 Naval Guns"

...snip...

I wasn't too concerned to bring your thread back onto track by suggesting bringing Hedy Lamarr to instruct the 4th Section about communications. I did like the discussion of the accuracy or otherwise of cruiser guns but didn't have much to contribute. The Hippers were significantly bigger and newer than most "Treaty cruisers" and I suspect that they had similar fire control apparatus to the Bismarck Class whilst for example American heavy cruisers (except the Alaskas) carried lighter, simpler and cheaper fire control equipment than the battleships. As mentioned earlier, Prinz Eugen matched Bismarck's shooting fairly closely at Denmark Strait which is impressive as Bismarck's shells had advantages such as being able to travel further under water and coming down less steeply.

If one reads http://www.fischer-tropsch.org/prim...Reports/USNTMJ-200F-0023-0085 Report O-31.pdf, the situation with IJN cruisers seems to have been slightly different with most heavy cruisers and most of the older battleships having the older Type 92 fire control equipment. Only Hiei (used as test ship), Yamato and Musashi are stated to have received the Type 98 equipment but perhaps the Mogami and Tone classes may also have received improved equipment. Even the best may not have worked perfectly. According to page 40, the Type 98 giro horizon showed problems with hunting in the follow up and gimbal friction. Thus the Type 1 giro horizon was produced but only as a single prototype which performed well at sea on the carrier Shinyo.

The anti-aircraft fire control http://www.fischer-tropsch.org/prim...Reports/USNTMJ-200E-0633-0764 Report 0-30.pdf showed similar problems of both performance and availability (see Enclosure E). While the Type 94 fire control was better than the Type 91, Nagato and Haruna were still fitted with the Type 91 in 1945 and there were apparently huge problems in producing enough Type 94 sets. In terms of what it did the Type 94 equipment was equivalent to the American Mark 37, and like it required rather a long time, 20 secs for the Type 94, to produce a solution. However, the American Mark 37 started to receive ranges from radar from late 1942 and the Royal Navy was already using radar ranges to improve its anti-aircraft accuracy in 1941 (RN equipment gave a quick and dirty answer rather than solving equations slowly and accurately like the Mark 37 or Type 94). One of the worse features of both the Type 91 and the Type 94 was that they depended on a separate optical range finder. When IJN ships came under attack by multiple enemy aircraft, it was discovered that nobody had realized pre-war that getting both the fire control telescope and the range finder to point at the same aircraft might be a problem. The Type 3 addressed many of the problems of the Type 94 and could give a much quicker solution while using radar ranges. However, it was never put into service. Destroyers and light cruisers used simpler (lighter and cheaper) systems such as the Type 2 for both HA and LA fire. However, that was not very effective as a HA system. Once more a new Type 5 system had been designed by 1945 with blindfire capacity but again it was not actually used. Meanwhile 25 mm guns on large ships and all guns on ships smaller than large destroyers were at best provided with the Type 95 or the related Type 4 fire control but the American report notes "It is curious that the Japanese Navy took no steps at all to design any other form of sight based on more advanced principles..."

Now to my devious plans. I intend to announce that the IJN will help to fund a program to deliver a television to every village before the celebration of 2600 years of the Empire Imperial Japan at Its Zenith: The Wartime Celebration of the Empire’s 2 ... - Kenneth J. Ruoff - Google Books and the Olympic Games in 1940. I also intend to fund the development of hearing aids to assist the naval gunners who often suffer hearing problems in later life. It has not escaped my notice that the British television industry was crucial in preparing Britain for large scale production of radar equipment after 1939 and that the success of America in producing proximity fuses that could be fired from a gun may have been greatly assisted by the development of a miniature value for hearing aids.

 

[parsifal]

I don't think that you have realized how stupid the IJN was with its codes. There is the issue of poor training. The additive tables of JN25B had 50,000 groups of numbers but 60% of the messages used the first 10,000 numbers as most clerks started on page 1 and as you mention they did not change the books often enough.

There is not much that is on par about IJN cipher security, but in practical terms how much worse were they? In the "This day In Europe" thread, ive been reading the DKM daily reports. By that time the B Dienst and other intelligence services were reading roughly 90% of RN and approximately 80% of the French Navy's "secure" signal traffic. These were being translated into uncannily accurate situation reports. not sure about DKMs intelligence on the USN and its merchant marines, but the few entries that do get entered in to the German Admiralty daily reports show remarkable details The effective difference between the Japanese and most of the allied navies in terms of their signal security was very minor.

What the Japanese were not prepreed for was the concerted effort the US put into breaking the codes, AND THEN PROCESSING THAT INFORMATION INTO SITUATION REPORTS OF DIRECT OPERATIONAL BENEFIT. neither were the Germans or Italians. The authors you are relying on are largely sensationalist in this regard, but in the end, Japanese SIGINT was overwhelmed rather than flawed in the first place. Not much they could do about that.

There is no sensible justification for having each code group divisible by three. If a transmission or decoding produced an error, there was only a one third chance that the erroneous group would be divisible by three. However, if the group cannot be found in the code book, it is clearly an error, and even with the divisibility by three, it is still not at all simple to guess what the correct group should be as any of the five numbers could be wrong. Clearly the IJN was reaching towards error checking codes but they were nowhere near getting that idea to work. They were, however, making their opponent's task much simpler. For example, occasionally the clerk would forget to add the superencipherment. Such signals were immediately identifiable as all the groups were divisible by three. The more mathematical consequences are explained in "The Flaw in the JN-25 Series of Ciphers, II" by Peter Donovan http://carma.newcastle.edu.au/jon/Preprints/Papers/Submitted Papers/Walks/Dirks notes/09duc1.pdf.

I did not know the details, but the results are pretty well known. Despite 10 years of effort, the USN had not had much success in deriving useful information from their reading of signal traffic. The qualities of the Yamato for example, were not known. The relative blindness was changed by two connected events. The first was the massive expansion in their SIGINT services, most notably in the analyst and interpretative areas. The intell just wasn't filed and forgotten anymore. Increasingly SIGINT was looked at, assessed and acted on. The second event, for the initial codebreaking effort was the enormous signal traffic generated by the April raids. how they did it is irrelevant. Until that US effort that swamped Japanese security, Japanise security was okay...not outstanding, poor in some respects. Once broken, the Japanese could not re-establish security nearly quickly enough. As the war progressed it became easier and easier to crack new codes. There was nothing the Japanese could have done about that.

As we both agree, there was no way a simple superenciphered code such as JN-25 could have resisted the sort of effort used against it (and the slightly better RN codes also fell to the Germans). However, I believe that using conversion squares plus a grille with enciphered indicators would have resisted solution during WW2 with the same frequency of replacement of code books as OTL.

It took three years for the RN to make a major dent on German SIGINT, what the German effort lacked were the resources to use that mountain of information they uncovered. allied security was little better than the Japanese....that needs to be remembered in this discussion. I don't know about the USN, but I would be very surpised that it was much better than the RN.

 

[cherry blossom]

...snip...
It took three years for the RN to make a major dent on German SIGINT, what the German effort lacked were the resources to use that mountain of information they uncovered. allied security was little better than the Japanese....that needs to be remembered in this discussion. I don't know about the USN, but I would be very surpised that it was much better than the RN.

The USN was better than the RN partly because they were richer and partly because they designed the most secure of the WW2 era cipher machines (although probably not the most reliable). Almost all major USN warships normally carried a ECM Mark II cipher machine which was completely secure during WW2 USS Pampanito - ECM Mark II. The USN was sufficiently worried about the possibility of an enemy capturing the ECM Mark II that submarines sent into shallow waters only carried less secure ciphers such as strip ciphers, CSP-642, and Hagelin derived machines. As even the capture of an ECM Mark II would not have imperilled USN codes, we can easily imagine how the choice to use a less secure cipher might have turned out badly. In fact CSP-642 turned out to survive IJN attacks and the USN may have calculated that they would see evidence in IJN signals if CSP-642 were to be broken. However, the USN may still have lost something as they may not have been able to send Ultra derived information to submarines using only the strip cipher.

We can go a little deeper into the security of strip ciphers. The strip cipher system used by the US State Department was broken or stolen by the Japanese Army, who naturally did not tell the Navy but did send details to Germany Christos military and intelligence corner: Cryptologic cooperation between Germany and Japan - The State Department's Strip cipher. The German analysis of the State Department system with new strips Christos military and intelligence corner: Compromise of the State Department's strip cipher in 1944 and Bauer's Decrypted Secrets, pages 248-50, give clues on how such ciphers could be attacked without too much aid from captures although Rohrbach's paywalled article presumably gives the details An Error Occurred Setting Your User Cookie. According to Bauer, the German attack did require "massive use of Hollerith punch card machines and of special equipment ...". For its attack on CSP-642, the IJN similarly used "IBM tabulators of the First Life and the Meiji Life Insurance companies" according to Kahn's Codebreakers, page 582, generally successfully determining the number of strips in use. However, little further progress was made and Kahn seems critical of the competence of the IJN codebreakers.

The Royal Navy had a relatively small but slowly increasing number of TypeX Machines Christos military and intelligence corner: The British Typex cipher machine for its most secure messages. TypeX was not broken during WW2 although it was not as secure as the USN's ECM II but could not be produced quickly enough to equip more than the important shore bases and major warships over most of WW2. Thus unlike the Americans and the Germans but like Japan, the RN used superenciphered codes rather than cipher machines for most messages and the RN codes were broken even pre-war by Germany. After RN codes were changed in August 1940 there was a see saw struggle until 1943 as B-Dienst continued to break into the new RN codes after they had been used for some time. It was only from late 1943 that RN codes improved to become secure after Enigma messages revealed the extent of German success against the earlier codes. The BAMS (Broadcast to Allied Merchant Shipping) code was also broken by both Germany and Japan after the capture of a codebook by the raider Atlantis.
ps. There is a good summary of British code security failures at http://chris-intel-corner.blogspot.gr/2014/02/british-cryptologic-security-failures.html

 

[N4521U]

Switched sides!

 

[cherry blossom]

Switched sides!

That is certainly a good idea, especially by 1941. However, one thing which doesn't change whichever side of WW2 the IJN ends up fighting on, is that they are going to need better anti-submarine warfare equipment and skills.

There were voices in the IJN advocating more effort on ASW. Niimi Masaichi was one such officer
https://books.google.co.uk/books?id...v=onepage&q=Niimi, Masaichi submarine&f=false. Niimi became a Vice-Admiral but does not seem to have been very influential. Kaigun goes on to mention Oi Atsushi as a younger officer with similar concerns. Another voice was Sato Ichiro, who was with Niimi in the 36th Class at Etajima and like him became a Vice-Admiral. In 1927, he showed that he understood Japan's vulnerability https://books.google.co.uk/books?id...ge&q=sato ichiro brassey naval annual&f=false. However, Sato also lacked influence and had retired before the Pacific War. There is a revealing analysis of his views at
https://books.google.co.uk/books?id...VP7VBcHvUqCigtAL&redir_esc=y#v=onepage&q=sato ichiro brassey naval annual&f=false.

The IJN's best sonar at the start of the Pacific War was the Type 93 Mod 3 The Pacific War Online Encyclopedia: Type 3 Model 1 Sonar but the older Type 93 Mod 1 introduced in 1933 was the equipment in general use. After the war had started, Germany gave the IJN details of its S-Gerät (drawings were carried on the I-30 which was sunk but the drawings were salvaged) and this was the basis of Type 3 The Pacific War Online Encyclopedia: Type 3 Model 1 Sonar produced from 1944. Clearly, the German sonar was superior to the Type 93 Mod 3 but it is not obvious how it compared with contemporary allied equipment. The S-Gerät had first been tested on German destroyers in 1938 and it is clearly highly desirable for the IJN to buy or steal plans of either the German or a British system around 1938.

The other issue is that the IJN needs to produce cheap but effective ASW vessels. The Tachibana Class http://en.wikipedia.org/wiki/Japanese_destroyer_Tachibana_(1944) and Ukuru Class http://www.combinedfleet.com/Ukuru_c.htm may have offered the best compromise of designs which saw production.

 

[parsifal]

Japanese SONAR was actually fairly efficient, as the attached USN Post War report suggests. it included elements of the latest (1941) technologies taken from captured british ships, as well as some German technologies and some of their own making

http://www.fischer-tropsch.org/prim...Reports/USNTMJ-200B-0343-0412 Report E-10.pdf

The problems with Japanese ASW was not so much their detection gear, though it could have been better. They lacked an effective ahead throwing AS weapon other than a fairly ineffective mortar adapted from an army ordinance. Training for ASW was more or less non-existent

The biggest problems with the Japanese ASW efforts were largely organizational and doctrinal. They failed to institute convoying until the middle of 1943, and did not have a dedicated Escort Command along the lines of the British Atlantic effort until September 1943. Even then, draftees into the command tended to be rejects from the surface navy in terms of personnel. Contrary to the popular myth, there was not really a shortage of escorts later in the war, roughly 700 vessels were built or converted for the purpose though the efficiency of many units was highly questionable. In terms of tactics, the Japanese failed to form proper hunter killer groups, or even retain the escorts in task groups so that they could develop effective team skills. Japanese escorts tended to blunder around the ocean depth charging indiscriminately with no object of corralling a contact into a planned AS trap. Sweeps tended to be of too short duration and not prosecuted with sufficient determination to be effective. Somewhere I very vaguley recall some sort of problem with the depth setting mechanisms of the DCs......

These weaknesses all tie in to the fact that convoy escort and ASW work did not fit into the IJN concepts of the decisive battle. A convoy battle meant a long war, and a long war meant Japan was going to lose. Certainly they could have done better, but its unrealistic to expect them to pour more resources into ASW in the pre-war build up when this was the sort of war they absolutely wanted to avoid.

 

[Garyt]

Late addition here, but what about a DE class that uses coal based engines? High speed is not a priority, a DE that runs at 20 knots is acceptable. This would help with the fuel issues 2 fold, both reduces consumption with the DE's and perhaps putting more of them at sea.

For that matter, what about having some CVE's with the same method of propulsion? Again, high speed is not a priority.

Even mixed propulsion of coal/oil could work if the coal based is too inefficient, though personally I think coal based DE's would work fine.

This idea reminds me a bit of Ben Franklin's idea to arm the colonies army with longbows and crossbows as opposed to muskets

 

[Shortround6]

Coal fired boilers using turbines don't have a big speed loss. You do need a bigger boiler room.

Reciprocating steam engines are where the speed loss comes from.

 

[Garyt]

Coal fired boilers using turbines don't have a big speed loss. You do need a bigger boiler room.

That's my point really. If they are designed as other escort vessels with the same amount of engine space, they will be slower.

But it would still seem to make sense I would think, for the oil starved Japanese Navy

 

[VBF-13]

Just my opinion, they spread themselves out too thin. They should have concentrated everything they had at Pearl, get us off of there. Then go get the rest.

 

[parsifal]

There wasnt a lot left to throw into Pearl really. It took the IJN roughly 18 months to train carrier qualified pilots, and the training establishment was a huge nut to crack if they wanted to change that. I forget the precise figures but Ive seen a memo from Yammomoto dated the end of April '42, complaining already about the shortages of pilots they were suffering. They were receiving something like 150 carrier qualified pilots per year from memory in 1940, and that was the yhear to look at for Japan in 1942. For the Americans it was a whole different ballgame. They had far better resources in their training programs, and dint view pilots as an expendable resource like the Japanese. For the USN, the pilots being trained in the latter half of 1941 are the ones that were manning their carriers 1942-3. They were a little under done in early'42, but US pilots learnt real quick, and the fact they were receiving pilots in the thousands compared to the Japanese few hundred made all the difference.

What the japanese threw at the Pacific fleet in December was about as much as they could muster. From there it was all downhill. By Midway, the big carriers were carrying approximately 15% less a/c than they had at Pearl, by the time of Eastern Solomons there was a partial recovery (because aircrew saved from the sunken carriers, but these too had been thrown on the fire. Thereafter replacement rates improved dramatically, but at the expense of quality. Aircrew in December 1941 had around 850 hrs of combat flying under their belts on top of around 500 hrs training time. Most of the air leaders had been flying since 1935-6. By the time of Phil Sea, there was virtually no combat time, and between 50-150 hrs of training hours. In that time, US pilot training had increased from around 250 training hrs to around 400 hrs, and combat times to an average of around 500hrs, up from nothing in 1941.

The pilots and machines manning the second line carriers in December 1941, the Zuiho, Hosho, Taiyo, Ryujo had already been combed out several times to build up the CAGs for the fast carriers. They lacked equipment, numbers, and skill to make much difference.

When I play sims of this scenario, as the Japanese, I actually hold back two of the fleet carriers and group them with the light carriers. I also dont comb out the CAGs of these smaller carriers. The four remaining fleet cariers that hit Pearl do a lot less damage, I dont even bother with a second strike over Pearl. I hit, then I run towards Midway. The two remaining fleet carriers plus the light carriers are escorting the Wake invasion forces to Midway, and the Guam invasion forces to Wake. Hitting midway early forces the USN into an unwinnable fight. They absolutely cannot allow the Japanese control of Midway that early, they have to implement some form of their plan Orange, and because the IJN carriers are concentrated, they usually destroy the USN fleet at sea more or less entirely. Game over from that point, provided the opponent silly enough to try and retake Midway. If they dont, there is a major security breach for Pearl, which is penalty enough in itself, but the Japanese move to isolate it from the rest of the TO by further occupations, Ellice, Gilberts, Johnston and Palmyra generally work to contain the major US supply and repair node very well. Keep a good part of your fleet at readiness at Kwaj, say 5 carriers, the rest at Truk on a training mission, building up spare CAGs as fast possible. Its admittedly unrealistic, but it at least points to some possibilities to an "alternative history".

 

[VBF-13]

What they brought to Pearl wasn't everything they had. Everything they had was spread out all over. I'm talking about surprising Pearl with everything they had, right on the jaw, but they didn't see it that way. Six months later was even almost too late for them. Had they been serious about taking the Hawaiian Islands, they'd have made it really tough. But instead that was just a hit and run to buy them some slack while they did their thing elsewhere. Had that not been viewed as an adjunct but as the main event and they'd have fortified it, they're five days away from the West Coast, and they cut us off from everything beyond the Islands, too. I just don't think they grasped the strategic importance of it. The Navy was doing the Army's bidding, there, really, for the most part, that's all that sneak attack was.

 

[parsifal]

Your thinking along the lines of a direct attack into Pearl. The army was never going to commit to the minimum 45000 assault troops they thought they might need for that, whilst the Navy thought it closer to 90000. To support a force projection of that magnitude, they needed to use every ton of shipping at their disposal then some. Post war studies suggest the navy was closer to the mark incidentally.

Direct invasion, if thats what you are angling for was a non-starter. The biggest operation the Japanese ever attempted, was in 1938 off Shanghai (or Hankow) I think, with about 25000 committed, and a couple of days sailing time from the Home islands. The japanese knew their limitations (well, sort of), and a direct assault was never within their capabilities. most competent post war studies Ive ever seen confirm that. That applies at any time, including just after the attack on Pearl. You do not attack a stronger opponent directly into the areas where he is most concentrated. that has about as much imagination, and about as much chance of success as one of Haigs "big pushes" on the Somme.

The only other option I can think of that you might be hinting at is some sort of comb out of the land based air (LBA) assets. Wasnt going to happen, more importantly couldnt happen unless the Japanese were prepared to abandon both China and Manchukuo, and risk economic ruin within 3 months of their DoW. Quite apart from that, there just wasnt the training assets available to even contemplate such a conversion. I can only repeat, the assets they have with respect to carrier capable air power was Japan actually punching above its weight, not falling short.

The problem with the attack at Pearl was that there was no follow up, nothing to force the US fleet into battle prematurely. by the time the Japanese had realized what they needed to do, it was far too late for them. A Midway option in December 1941, or a similar location as Midway, would force the Americans to play ball when they couldnt. Sink the 1941 US Pacific Fleet as the Japanese and you really do win your war. I agree with Yammamoto however, in the long term, Japan could not defeat the US, therefore they should not fight the US. Any amount of victory in 1941 and 1942 is not going to change the long term outcome. From that perspective, Pearl Harbour was national Seppuku.

.

 

[VBF-13]

Your thinking along the lines of a direct attack into Pearl. The army was never going to commit to the minimum 45000 assault troops they thought they might need for that, whilst the Navy thought it closer to 90000. To support a force projection of that magnitude, they needed to use every ton of shipping at their disposal then some. Post war studies suggest the navy was closer to the mark incidentally.

Direct invasion, if thats what you are angling for was a non-starter. The biggest operation the Japanese ever attempted, was in 1938 off Shanghai (or Hankow) I think, with about 25000 committed, and a couple of days sailing time from the Home islands. The japanese knew their limitations (well, sort of), and a direct assault was never within their capabilities. most competent post war studies Ive ever seen confirm that. That applies at any time, including just after the attack on Pearl. You do not attack a stronger opponent directly into the areas where he is most concentrated. that has about as much imagination, and about as much chance of success as one of Haigs "big pushes" on the Somme.

The only other option I can think of that you might be hinting at is some sort of comb out of the land based air (LBA) assets. Wasnt going to happen, more importantly couldnt happen unless the Japanese were prepared to abandon both China and Manchukuo, and risk economic ruin within 3 months of their DoW. Quite apart from that, there just wasnt the training assets available to even contemplate such a conversion. I can only repeat, the assets they have with respect to carrier capable air power was Japan actually punching above its weight, not falling short.

The problem with the attack at Pearl was that there was no follow up, nothing to force the US fleet into battle prematurely. by the time the Japanese had realized what they needed to do, it was far too late for them. A Midway option in December 1941, or a similar location as Midway, would force the Americans to play ball when they couldnt. Sink the 1941 US Pacific Fleet as the Japanese and you really do win your war. I agree with Yammamoto however, in the long term, Japan could not defeat the US, therefore they should not fight the US. Any amount of victory in 1941 and 1942 is not going to change the long term outcome. From that perspective, Pearl Harbour was national Seppuku.

.

The Midway force brought in a landing force. That was at a time when they thought they had the drop on us, as well. The Hawaiian Islands would have been greater in magnitude, obviously. It would have required an unprecedented commitment in resources, there's no question about that, just look at the troop estimates you supplied. Still, they had surprise on us. The branches weren't on the same page for it. Had they thought on an invasion, considered it, it wasn't much. They needed a commitment for that. That's the first thing they were lacking. They should have taken it, just as they took the Philippines. They could have, IMO, had they concentrated everything there. Instead, they kicked it, and had their fingers crossed we'd capitulate, but, instead, we mobilized. Six months go by, they try to get us, again, at least attract our big carriers, and get them out of the way. It's dragging on. They hadn't planned on it. After Midway, at least, they probably had a different plan on the books, every month. They're fighting a battle of attrition. And we're in a full-employment cycle, and throwing more at them than they can handle. Ah, hindsight...

 

[Shortround6]

They should have taken it, just as they took the Philippines. They could have, IMO, had they concentrated everything there. Instead, they kicked it, and had their fingers crossed we'd capitulate, but, instead, we mobilized. Six months go by, they try to get us, again, at least attract our big carriers, and get them out of the way. It's dragging on. They hadn't planned on it.

The problem for the Japanese is that it is a major gamble because they cannot invade Hawaii and the Philippines at the same time. Assuming they are successful in Hawaii it is going to be 2-4 months before they can invade the Philippines and the real goal, the Dutch East Indies oil fields. The Japanese have a very limited amount of oil until they can get the oil fields under their control. Giving the defenders in the South East Asia 2-4 more months to dig in/prepare won't make them invulnerable but it would allow them to make a better showing than they did. Delaying the capture of the oil fields even more. They are in a race against time not only against the US getting it's production up and rolling but in getting the oil fields under control and producing before their fleet just runs out of fuel in mid ocean,so to speak.

 

[VBF-13]

The problem for the Japanese is that it is a major gamble because they cannot invade Hawaii and the Philippines at the same time. Assuming they are successful in Hawaii it is going to be 2-4 months before they can invade the Philippines and the real goal, the Dutch East Indies oil fields. The Japanese have a very limited amount of oil until they can get the oil fields under their control. Giving the defenders in the South East Asia 2-4 more months to dig in/prepare won't make them invulnerable but it would allow them to make a better showing than they did. Delaying the capture of the oil fields even more. They are in a race against time not only against the US getting it's production up and rolling but in getting the oil fields under control and producing before their fleet just runs out of fuel in mid ocean,so to speak.

That's right. Throw in the rubber plants, too. The raw materials were the main event. The Japanese swept through that region because of the element of surprise, principally. Could they have done both, and got Hawaii, too? I'll concede, it would have taken more than they threw at MacArthur.

 

[cherry blossom]

That's right. Throw in the rubber plants, too. The raw materials were the main event. The Japanese swept through that region because of the element of surprise, principally. Could they have done both, and got Hawaii, too? I'll concede, it would have taken more than they threw at MacArthur.

Don't give too easily!

As far as sane sensible military leaders were concerned, Hawaii was beyond Japan's reach.

However, if we want innovative alternate history, we might turn to Glen239's famous Operation Tinkerbell, which we can find for example at The invasion of Oahu, December 1941. - Axis History Forum and Operation Tinkerbell preliminary: calculating shipping costs in Battleship Vs Battleship Forum.

One of Glen's insights was that December 1941 was special in that most of the Japanese merchant fleet was idle and thus available to transport troops and supplies. Now clearly, the attack on Malaya and the Netherlands East Indies could not be delayed as the capture of the oil fields was critical. However, it was only necessary to prevent American forces on the Philippines from attacking Japanese ships, which could be done by bombing as occurred historically. The actual invasion of the Philippines could be delayed for months. Similarly, there was no urgency in attacking Guam or the British held Gilberts.

Another surprising observation was that there were essentially undefended airfields on several islands in the Hawaii Chain, with only Oahu having a significant garrison (note that the Japanese leaders probably never imagined that such airfields would be undefended). Thus Glen came up with the idea of Japanese troops landing on the other islands shortly after the Pearl Harbor attack and establishing bases. As the Japanese Fleet would have to stay around, it would probably encounter any USN ships that were at sea and that remained in the vicinity; in particular Enterprise and Lexington. Thus it is quite plausible that Japan can create a situation in which the control of the waters around Oahu and the air above are contested on fairly equal terms. As both fleets will depend on bases two thousand miles away, control may swing back and forth. However, the IJN was at its strongest relative to the USN just after Pearl, so the IJN may control the sea most of the time.

Could the IJN achieve anything else. Well they could bombard Oahu and sink any surviving ships in Pearl. Surely not! What about the coastal artillery? Well once again we find that America was not quite ready for war. The guns were all in the open and could be disabled by the Kido Butai's dive bombers.

But could Japan take Oahu? Well that is the hard question. The IJA would certainly find it hard to establish itself on Oahu. The IJA and SNLFs did make successful landings against some opposition, for example, at Kota Bharu in December 1941 or on Hainan Island in February 1939. However, they did not have the training and techniques of 1944-5 US Marines. The biggest difference may have been that IJN ships had not practised supporting landings and there was no radio communication from the shore to call for gunfire support. Off Hainan, instead of directly supporting, the IJN bombarded communications according to a rigid plan during the night landing. Clearly a night landing, perhaps further screened by smoke, would make getting ashore through the Hawaiian surf even more exciting. At Shanghai, the IJN was willing to bring its ships close to the shore when Japanese infantry were pinned down. However, the problem off Oahu is that there may be many other things for IJN ships to do. OTL Japanese amphibious tank development Type 2 Ka-Mi - Wikipedia, the free encyclopedia was also running too slowly to assist unless we add a POD that planning begins well before late 1941. Thus a landing may well fail. However, if some Japanese forces are established ashore and can be supplied, it seems likely that the US forces will be worn down as they cannot be easily resupplied.