Just how good or bad was the IJN during WW2?

[ray245]

While the IJN achieved a number of success against the allied navies at the start of the war, it remained plagued with numerous issues, ranging from pilot training to issues concerning fuel.

While the war in Europe allowed Japanese to invade SEA while the colonial powers were distracted, it provided the Japanese with a much easier time in invading SEA. Would the Japanese navy even be able to push back the navies of the European powers if they aren't focusing all their attention in Europe?

[Borgholio]

If Europe was not at war and it was the world vs Japan, they would crumble pretty fast. The IJN had some successful ships and some fine pilots, but they were always lacking in the industrial and recruitment areas. They simply could not replace the ships or the trained pilots that they lost. That's partly why they went to the Kamikazes - they couldn't train enough pilots to actually mount a proper attack on the US ships. So if Japan started getting aggressive and the other Pacific powers weren't distracted by the battle of the Atlantic, then I would say the Japanese might not even start a conflict and if they did, their expansion would not be nearly as quick as it was IRL.

[Isolder74]

Yamamoto knew from the outset that they didn't have a chance against the US Navy right from the outset unless he managed to knock out the US Navy very quickly and right from the start. This is why he planned and executed the attack on Pearl Harbor in the first place. This why he risked so much on the Battle of Midway hoping to finish the job.

Even if we ignore the British, they didn't have a chance and everyone in the Japanese Navy knew it. They did manage some early victories but once the US got the war machine rolling, they were crushed. Even before that the sausage grinder that was Guadalcanal was the beginning of the end for the Japanese. Remember because of the long and high standards that the Japanese place on themselves for pilot training for the Naval Air Service they could only train 100 or so new combat ready pilots a year. Even with emergency streamlining of their training system they still could only get up to 300 in a year.

Where the US and British could replace their losses, every ship, man and aircraft lost was a liability for the Japanese that they couldn't easily replace. This was extremely the case when it comes to their carrier pilots who they could not replace for the duration of the war. Every experienced pilot lost simply meant their carriers became less and less of a viable strategic weapon just when they would be needing them the most. In fact they entered Midway 2 carriers short because of the pilot losses from Coral Sea. While they might have repaired the battle damage to the Shikoku, they needed months to fill the pilot seats again. Contrast that with Yorktown which was repaired and fully back in action(and manned) for the Midway battle.

[Simon_Jester]

A worthwhile footnote to this is that at some point "high training standards" becomes "has hit the point of diminishing returns." Training your pilots twice as hard doesn't make them twice as deadly, once you get past... I don't know, the first 10-100 hours of pilot training. And to a large extent, getting that level of training is about having sufficient fuel for training, and about having experienced instructors on hand. It's not magic, though obviously a nation with limited fuel reserves has trouble with it.

So it's not (as some Internet morons think) a case of "the Japanese pilots were UBERLEET SUPERMEN who were worn down by sheer numbers." When fighting American carrier pilots in the Coral Sea, against aircraft no better than what the US had at Pearl Harbor, the prewar "elite" Japanese pilots didn't manage particularly disproportionate casualty ratios, after all.

It's more like "Japan made questionable decisions about how to train pilots, with the consequence that unlike every other WWII power, they could not produce more pilots on demand."

Sort of like how German surface warships weren't UBERLEET SUPERSHIPS worn down by sheer numbers. Nope, they were just plain outnumbered, while not actually being stronger or better than most of their opponents of comparable vintage.

[BabelHuber]

This is a good link which shows why Japan basically didn't have a chance: http://www.combinedfleet.com/economic.htm

On top of it, Japan compounded their problems by trying to create 'superiour' warships like the Yamato-class: This was intended to even the odds, since Japan would have warships at hand which were individually superiour to their counterparts.

However, in real life this means that Japan produced even less war ships than otherwise. Having 2 North Carolina-type ships is usually better than having 1 Yamato-class ship, since 2 ships can be at 2 locations at 1 time or combine their strengths in 1 place, while a single ship can only be at 1 place at a time.

Also, when you lose a more expensive ship, it hurts more.

My best guess is that Japan tried to repeat the 1905 success against Russia. In 1905, Russia was also economically superiour, but after losing at Tsushima stopped fighting. So Japan probably thought that the USA would react similarily after Pearl Harbor.

This is an insane strategy, but at least would have some basis in reality. Everything else I can think of is just plain madness on Japan's part.

[Isolder74]

To put it into perspective, the Japanese expected their pilots to have at least 200 hours of flight time before they could even be considered for carrier pilot training then on top of that at least 300 flight hours of carrier flight practice before they were even considered for carrier service. This is the minimum to just get out of flight school and does not include all of the flight time they used for follow up combat training(up to 350 hours itself) after being assigned to a ship. This was one reason why the oil embargo was considered such a big deal for them as it drastically curtailed all of their training programs. It was not helped that only specially selected candidates were even selected for entry into the programs in the first place making the situation even worse.

All the post Midway streamlining did was cut those requirements in about half and double the size of the training classes.

Meanwhile, the British and Americans are throwing as many flight candidates at the training schools as they could muster so even if they trained to the same degree of intensity(which of course they didn't) they would have still come out on top. Even then it quickly got to the point that even a green US Navy pilot could run circles around a hastily trained green Japanese pilot by 1943 and onward.

[Tribble]

To put it into perspective, the Japanese expected their pilots to have at least 200 hours of flight time before they could even be considered for carrier pilot training then on top of that at least 300 flight hours of carrier flight practice before they were even considered for carrier service. This is the minimum to just get out of flight school and does not include all of the flight time they used for follow up combat training(up to 350 hours itself) after being assigned to a ship. This was one reason why the oil embargo was considered such a big deal for them as it drastically curtailed all of their training programs. It was not helped that only specially selected candidates were even selected for entry into the programs in the first place making the situation even worse.

All the post Midway streamlining did was cut those requirements in about half and double the size of the training classes.

Meanwhile, the British and Americans are throwing as many flight candidates at the training schools as they could muster so even if they trained to the same degree of intensity(which of course they didn't) they would have still come out on top. Even then it quickly got to the point that even a green US Navy pilot could run circles around a hastily trained green Japanese pilot by 1943 and onward.

Not to mention pilot safety was generally regarded as an afterthought, if not outright discouraged. No armour, no self-sealing fuel-tanks, limited attempts at rescuing downed pilots and a culture which promoted a glorious death in combat as the best way to go certainly didn't help.

One area where Japan was outclassed was radar; although they had radar, its development generally lagged behind the Allies and even Germany.

Also, the Japanese naval codes had been broken by the Americans even before Pearl Harbour. One of the reasons why the IJN task force went undetected was because the IJN employed complete radio silence in the days leading to the attack. The cracking of the Japanese naval codes certainly had a big impact; for example, Yamamoto dispersed his forces at Midway hoping to throw the Americans off balance, but the Americans deciphered the true target, ignored the feints, and concentrated their forces at the IJN carrier group.

Perhaps the biggest impact on the war is the one that's rarely talked about, which was the Allied campaign against Japanese shipping. The Japanese placed a low priority on protecting their merchant fleet, and the Allies exploited it to the full. IIRC, more than 75% of Japan's merchant fleet was sunk by the end of the war. Even if they had somehow maintained superiority in terms of warships, their economy would have collapsed due to lack of shipping. They really had no chance.

[ray245]

How well could Japan fair against a full undistracted Royal navy alone, assuming the US stay well out of the war?

[Thanas]

You might find this thread interesting.

[Elheru Aran]

My understanding of the situation is that the majority of the Japanese arms were state of the art... for the 1930s. That was part of what doomed them in the end, along with simply being incapable of keeping up with the sheer volume of Allied production lines. They had many early gains through surprise, a minor element of strategic genius (they really did have some very good officers in the early part of the war), and a fairly consistent war plan that involved techniques which maximized their limited numbers (ambush, trench/bunker warfare, shock attacks).

That was negated mostly by a lack of serious upgrades as the war went-- Japanese technology and industry never managed to come up to the standards that American and British industry reached in the 1940s or sometimes even 30s (note that a number of their aircraft were directly inspired by German fighters, most notably the Tony)-- steadily decreasing quality of munitions and troops on their side, increasing quality of troops on the Allied side, and again, the flat out ridiculous volume that the USA (mostly) was cranking out of ships, aircraft, tanks, guns, what have you. The moment things turned around for the Allies at Midway, the Japanese were absolutely punching way above their level, and their end was highly inevitable.

[Simon_Jester]

This is an insane strategy, but at least would have some basis in reality. Everything else I can think of is just plain madness on Japan's part.

From the point of view of a bunch of foreigners with little knowledge of Russian or American culture, there would be no obvious reason to expect the Americans to keep fighting when the Russians didn't.

Meanwhile, the British and Americans are throwing as many flight candidates at the training schools as they could muster so even if they trained to the same degree of intensity(which of course they didn't) they would have still come out on top. Even then it quickly got to the point that even a green US Navy pilot could run circles around a hastily trained green Japanese pilot by 1943 and onward.

About how many hours did the Americans receive? But yeah, once you get to the point where your carrier pilots can take off and land on the ship reliably, and at least avoid the most obvious mistakes in a dogfight, you benefit more from getting them into the field than not.

I believe this is compounded by the fact that the vast majority of air-to-air kills were being scored by a handful of "aces," and that it's hard to identify an "ace" in advance. Getting more pilots out there meant that the minority of aces get an opportunity to show their stuff (and survive over long periods to rack up very high kill rates), whereas holding them in training and dribbling out pilots to the carriers a few at a time reduces the effect. Since it was seemingly impossible to turn normal pilots into aces just by training them harder, you didn't benefit from training past a certain point.

And, yeah, lack of aircraft and pilot safety doesn't help either. If you're going to train an elite you have to keep them alive, or there's no point in even bothering to train them- there's a reason why warrior aristocrats in feudal warfare traditionally wear armor.

[ray245]

It really does seem surprising that the Japanese maintained an imperialistic ambition to control East Asia despite having a far weaker navy than almost every rather rivalling powers in the region. In other words, the only hope of a successful invasion of SEA lies entirely on an extremely lucky set of events to begin with.

They have to hope the war in Europe would be able to keep the French and the British occupied while requiring a decisive strike against the US navy, while not having any major allies that could aid them directly in the Pacific. Looking at the IJN operations during WW2, it is hard to see many operations that could be seen as a major success after Pearl Harbour.

Almost every other naval engagement they fought in resulted in a dismissing ability of the IJN to conduct any future operation successfully.

[Elheru Aran]

It really does seem surprising that the Japanese maintained an imperialistic ambition to control East Asia despite having a far weaker navy than almost every rather rivalling powers in the region. In other words, the only hope of a successful invasion of SEA lies entirely on an extremely lucky set of events to begin with.

They have to hope the war in Europe would be able to keep the French and the British occupied while requiring a decisive strike against the US navy, while not having any major allies that could aid them directly in the Pacific. Looking at the IJN operations during WW2, it is hard to see many operations that could be seen as a major success after Pearl Harbour.

Almost every other naval engagement they fought in resulted in a dismissing ability of the IJN to conduct any future operation successfully.

That's more or less the case-- they were counting on swift, decisive surprise victories to sweep the Allies out of the way in the East. After that point, their main hope was that the Germans and Italians would keep everybody busy in Europe and Africa. They had set up some groundwork for the future in occupying Korea and a good chunk of China by that point.

Yamamoto was perfectly aware though that once the Japanese engaged the United States, they were screwed. A number of the higher level officers were quite aware of this as well, but political expediencies dictated that they obey their authorities' imperialistic ambitions and keep schtum about any doubts they might have.

[Isolder74]

About how many hours did the Americans receive? But yeah, once you get to the point where your carrier pilots can take off and land on the ship reliably, and at least avoid the most obvious mistakes in a dogfight, you benefit more from getting them into the field than not.

I believe this is compounded by the fact that the vast majority of air-to-air kills were being scored by a handful of "aces," and that it's hard to identify an "ace" in advance. Getting more pilots out there meant that the minority of aces get an opportunity to show their stuff (and survive over long periods to rack up very high kill rates), whereas holding them in training and dribbling out pilots to the carriers a few at a time reduces the effect. Since it was seemingly impossible to turn normal pilots into aces just by training them harder, you didn't benefit from training past a certain point.

And, yeah, lack of aircraft and pilot safety doesn't help either. If you're going to train an elite you have to keep them alive, or there's no point in even bothering to train them- there's a reason why warrior aristocrats in feudal warfare traditionally wear armor.

American Pilots standard was 50 - 100 hours flight time(one successful landing was usually enough to clear a pilot for deployment) including carrier take off and landings. The way the American schools were set up also increased the proficiency of the training schools the longer the war went on. Periodically, the Americans would rotate their aces back to the training schools as instructors. The Japanese kept their pilots in combat operations until they were killed meaning any important information tactically they had learned in combat was never passed on to newer pilots. Nearly every pilot in the Great Marianas Turkey shoot on the American side were combat veterans facing 90% green Japanese replacements. They still had a few of their combat veterans still around but most of them were now gone.

The motto of the Japanese pilot training was "Train Hard, Fight Easy" something that worked out for them initially. However as the war went on and the Allies sunk tanker after tanker it only got worse for them. One of the factors that helped lose them the Battle of Midway was fuel shortages meant that the new pilots in the first strike wave had not been able to practice bombing land targets so their initial strike against the Midway Airfields was not able to take them out of action. All during the war, the Japanese showed less then normal capability at destroying Allied ground facilities. They could take out planes and buildings just fine but they struggled to knock out roads and airfields.

[Lord Revan]

This is an insane strategy, but at least would have some basis in reality. Everything else I can think of is just plain madness on Japan's part.

From the point of view of a bunch of foreigners with little knowledge of Russian or American culture, there would be no obvious reason to expect the Americans to keep fighting when the Russians didn't.

in defense of the Japanese High Command, USA(or more precise the american people) had made their dislike for a new war very clear (yes as hard as it might seem to imagine there was a time when USA didn't want to start/join wars for shits and giggles), in fact IIRC the whole deal with the "lend/lease" laws was to give USA ability to assist the allies without giving the impression of "getting american boys killed in another european war", so the idea of a Pearl Harbor style attack wasn't that bad in paper.

What the Japanese misjudged totally was the reaction of the american people for getting attacked on essentially their own soil. It should be noted that Japanese leaders who had knowledge of american culture were less optimistic about their chances, but Japanese High Command/goverment at the time had large amount of arrogance so they dismissed the warnings of those members of who were less then optimistic about their chances.

[BabelHuber]

From the point of view of a bunch of foreigners with little knowledge of Russian or American culture, there would be no obvious reason to expect the Americans to keep fighting when the Russians didn't.

These foreigners must be utter morons, then

In 1905, the Tsar was weak, Russia had some strikes and other unrests pre-war and after the battles of Tsushima and Mukden, a revolution-like situation occured.

A strong Tsar who had the support from the Russian population would have been able to crush the Japan army first, then rebuild the Russian fleet and crush the Japan navy a few years down the line. The only hope of Japan would have been support from Great Britain in this case, and even then they would have lost Korea.

So taking 1905 as a blueprint to attack a country with an industrial output which is literally more than an order of magnitude higher than Japan's is a recipe for disaster.

This plan only has a chance to work if the attacked country refuses to fight, and we all know how this ended.

[Simon_Jester]

From the point of view of a bunch of foreigners with little knowledge of Russian or American culture, there would be no obvious reason to expect the Americans to keep fighting when the Russians didn't.

These foreigners must be utter morons, then

In 1905, the Tsar was weak, Russia had some strikes and other unrests pre-war and after the battles of Tsushima and Mukden, a revolution-like situation occured.

A strong Tsar who had the support from the Russian population would have been able to crush the Japan army first, then rebuild the Russian fleet and crush the Japan navy a few years down the line. The only hope of Japan would have been support from Great Britain in this case, and even then they would have lost Korea.

So taking 1905 as a blueprint to attack a country with an industrial output which is literally more than an order of magnitude higher than Japan's is a recipe for disaster.

This plan only has a chance to work if the attacked country refuses to fight, and we all know how this ended.

The power of hindsight, it is stunning...

The Japanese strategy was certainly bad strategy, simply because taking big gambles with your national well-being on the grounds that the gamble paid off before is a stupid plan.

But when the Japanese made the decision to commit to war in late 1941, there was actually quite a lot of evidence they could interpret to support for the hypothesis that democracies lacked the will to efficiently prosecute protracted wars against militarist dictatorships.

They were wrong to conclude that, but the decision does reflect an interpretation of the world that, at this time, was widely shared including among citizens of the democracies.

[BabelHuber]

The power of hindsight, it is stunning...

The Japanese strategy was certainly bad strategy, simply because taking big gambles with your national well-being on the grounds that the gamble paid off before is a stupid plan.

Calling this a bad plan is the euphemism of the day.

But when the Japanese made the decision to commit to war in late 1941, there was actually quite a lot of evidence they could interpret to support for the hypothesis that democracies lacked the will to efficiently prosecute protracted wars against militarist dictatorships.

Which evidence was this? Great Britain resisted the Nazis. France, Netherlands, Belgium etc. were overrun, so they couldn't keep on fighting. This is independent of the form of government.

They were wrong to conclude that, but the decision does reflect an interpretation of the world that, at this time, was widely shared including among citizens of the democracies.

In WW1, quite a few democracies took part. It's true that these countries were all weary of wars and wouldn't start another one light-heartedly in the 1930ies. But this doesn't mean that they won't fight no matter what.

I'd assume that Japan did have some actual experts to help the government in decision-making. So, these experts should have come to the conclusion that if the USA stays in the fight, Japan has no chance at all. Even Yamamoto knew this.

Under such conditions, you don't start a war.

[Simon_Jester]

The power of hindsight, it is stunning...

The Japanese strategy was certainly bad strategy, simply because taking big gambles with your national well-being on the grounds that the gamble paid off before is a stupid plan.

Calling this a bad plan is the euphemism of the day.

Nonetheless descriptive.

It was a bad plan. It was also a stupid plan. However, it was a plan that was informed by some things that many non-Japanese sincerely believed, or at least feared, to be true at the time.

But when the Japanese made the decision to commit to war in late 1941, there was actually quite a lot of evidence they could interpret to support for the hypothesis that democracies lacked the will to efficiently prosecute protracted wars against militarist dictatorships.

Which evidence was this? Great Britain resisted the Nazis. France, Netherlands, Belgium etc. were overrun, so they couldn't keep on fighting. This is independent of the form of government.

At the time, the thesis was widespread that France, Belgium, the Netherlands, Denmark, and Norway had all been overrun largely because they were relatively pacifist and 'weak' nations, whose democratic governments had failed to adequately prepare for war because they were unwilling to take risks or expend resources to make the preparations.

Frankly, that theory had considerable supporting evidence, since all those nations were unprepared for war when it broke out, and in particular the Norwegians and the French wound up putting up much less of a fight than they could have, on account of lacking the means to resist as efficiently as might have been possible.

They were wrong to conclude that, but the decision does reflect an interpretation of the world that, at this time, was widely shared including among citizens of the democracies.

In WW1, quite a few democracies took part. It's true that these countries were all weary of wars and wouldn't start another one light-heartedly in the 1930ies. But this doesn't mean that they won't fight no matter what.

I'd assume that Japan did have some actual experts to help the government in decision-making. So, these experts should have come to the conclusion that if the USA stays in the fight, Japan has no chance at all. Even Yamamoto knew this.

Under such conditions, you don't start a war.

Bluntly, the Japanese fell prey to one of the worst cases of groupthink in recorded history, convincing themselves to massively cherrypick evidence in favor of the desired conclusion that the Americans would lack the will to fight a protracted war.

My point is simply that this evidence was not purely a product of their own insanity- they were exaggerating a belief that was shared by quite a few citizens of other countries, not just inventing a belief unique to themselves.

[Lord Revan]

We should also remember that USA at the time was just recovering from the great depression and was very anti-war. So it wasn't like USA was looking for an excuse to start a war with Japan, in fact it was quite the opposite.

Also we should remember that League of Nations (the toothless predesessor of the UN) had made impotent protests about the Japanese invasions of China, which probably enforced the notion of the western nations being weak in the eyes of the japanese hardliners.

Pearl Harbor was also not meant to be the start of long and bloody war but rather both the start and end of the war, the idea of the japanese commanders was to scare USA enough that they'd sue for peace on japanese terms.

So the japanese did misjudge the character of the american people but it wasn't a judgement without any merit.

[Sea Skimmer]

All during the war, the Japanese showed less then normal capability at destroying Allied ground facilities. They could take out planes and buildings just fine but they struggled to knock out roads and airfields.

That really came down to simple tonnage on target, Japan really was a fifth rate power on that subject. Even Italy could muster heavier bombing. Japanese accuracy strafing and bombing with the early war pilots could improve results against point targets like planes and ships but this meant nothing against area targets. Also even with skilled pilots, Japanese aircraft encountered rapidly much much heavier levels of anti aircraft fire.

Look at how nearly all Japanese twin engine bombers could only carry an 800kg bomb load. I don't think any single engine plane they had could do over 800kg at all except perhaps certain suicide plane conversions.

That's less then a P-40 Tomahawk could carry as a fighter bomber, and some late war US planes could get off the ground with two 2000lb bombs if they really wanted. With moderate payloads, just enough in fact for a torpedo, Japanese could destroy point targets like aircraft on the ground given a chance but they were just never going to be able to mount sustained bombing campaigns against anything. Japanese 4 engine flying boats in some cases had much heavier armaments, but they were few in number and badly needed as scouts.

By mid 1943 AIRSOL command, the Allies Soloman Island based collective land air power could put up 90 x B-24 raids, with even higher numbers of escort fighters. Japan could actually match this plane for plane in the air, but the B-24 strike would deliver anything from 250-500% more tonnage over the target depending on the range. This was besides what allied planes in New Guinea could do. Japan never had over ~500 planes total at one time in the combat theater around Rabaul.

So that's why you get constant Japanese air raids but not so much destruction, they just really aren't dropping many bombs and takes tremendous numbers to accomplish anything.

[BabelHuber]

At the time, the thesis was widespread that France, Belgium, the Netherlands, Denmark, and Norway had all been overrun largely because they were relatively pacifist and 'weak' nations, whose democratic governments had failed to adequately prepare for war because they were unwilling to take risks or expend resources to make the preparations.

Frankly, that theory had considerable supporting evidence, since all those nations were unprepared for war when it broke out, and in particular the Norwegians and the French wound up putting up much less of a fight than they could have, on account of lacking the means to resist as efficiently as might have been possible.

Sure, these countries lacked preparation, which was one reason they were overrun quickly by the Nazis. Today we have some additional information, like that France had significantly more tanks than Germany, but failed to use them in a sane way. Or that the German command structure was vastly superiour to the French counterpart.

These facts most likely were not known by the Japanese government in 1941.

But it should have been known in 1941 that overrunning a country which lacks preparation is one thing, and performing an unprovoked sneak attack without being able to invade further is a completely different story.

In the latter case, the aggressor can only watch as the attacked country ramps up production and mobilizes its forces. And when your enemy has an order of magnitude advantage in production, this cannot turn out well.

Bluntly, the Japanese fell prey to one of the worst cases of groupthink in recorded history, convincing themselves to massively cherrypick evidence in favor of the desired conclusion that the Americans would lack the will to fight a protracted war.

My point is simply that this evidence was not purely a product of their own insanity- they were exaggerating a belief that was shared by quite a few citizens of other countries, not just inventing a belief unique to themselves.

The Japanes government, like Nazi Germany, had delusions of grandeur. I think that this led to decisions which were insane in hindsight, but at the same time a rational observer in 1941 would have known that the Japabnese attack on the USA can only lead to disater.

[ray245]

Looking at some of the problems the Japanese navy faced, it seems that they have problems even if they were to wage a purely defensive war against any determined opponents.

Any opponent seeking to eliminate the Japanese navy could very easily force the navy into port and deny them fuel supplies from operating.

[Isolder74]

Looking at some of the problems the Japanese navy faced, it seems that they have problems even if they were to wage a purely defensive war against any determined opponents.

Any opponent seeking to eliminate the Japanese navy could very easily force the navy into port and deny them fuel supplies from operating.

This is more or less what did happen during the war. Almost all of their heavy ships ended up needing to be based in Singapore or elsewhere in Indonesia where they were in easy access of the oil fields there. Before the Battle of Leyte Gulf, the carriers were only in Japan to try and refill lost pilot rosters as they desperately tried train replacements. They had no problem rebuilding the aircraft but those are useless without pilots.

During the Leyte battle, many of Ozowa's pilots had only managed one carrier landing some never at all(which means he could only guarantee one real strike). Just before the battle, in response to American moves in preparation for the Phillipians invasion, Toyota had committed the bulk of the 300 carrier pilots(ones with full carrier capability) they'd just finished training to attacks losing most of them with little to no actual strategic value. Some of those pilots simply lost at sea trying to attack ships they weren't even sure where they were. This didn't stop the Japanese military claiming to have sunk several carriers and battleships to the Japanese public.

[ray245]

Looking at some of the problems the Japanese navy faced, it seems that they have problems even if they were to wage a purely defensive war against any determined opponents.

Any opponent seeking to eliminate the Japanese navy could very easily force the navy into port and deny them fuel supplies from operating.

This is more or less what did happen during the war. Almost all of their heavy ships ended up needing to be based in Singapore or elsewhere in Indonesia where they were in easy access of the oil fields there. Before the Battle of Leyte Gulf, the carriers were only in Japan to try and refill lost pilot rosters as they desperately tried train replacements. They had no problem rebuilding the aircraft but those are useless without pilots.

During the Leyte battle, many of Ozowa's pilots had only managed one carrier landing some never at all(which means he could only guarantee one real strike). Just before the battle, in response to American moves in preparation for the Phillipians invasion, Toyota had committed the bulk of the 300 carrier pilots(ones with full carrier capability) they'd just finished training to attacks losing most of them with little to no actual strategic value. Some of those pilots simply lost at sea trying to attack ships they weren't even sure where they were. This didn't stop the Japanese military claiming to have sunk several carriers and battleships to the Japanese public.

From a grand strategy perspective, the IJN is basically an ineffective force against almost any other navy other than weak naval powers. They can't afford to defend the home Islands because they will be cut off from fuel otherwise. They can't mount much of an offensive either against a fully operation enemy navy because their fuel limits their operations. They can't defend their SEA poessession because they will simply be outproduced by their foes anyway.