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HOI4 (Hearts of Iron IV): Japan Guide – China and Beyond

HOI4 (Hearts of Iron IV) Japan Guide - China and Beyond

Hearts of Iron IV, the latest installment in Paradox Interactive’s beloved series, thrusts players into the epic theater of the Second World War. Challenged by formidable adversaries, gamers assume the role of leaders, steering their nations through the trials and tribulations of humanity’s most extensive conflict, aiming to achieve ultimate triumph. Among the influential forces of the era, Japan stands tall as the predominant East Asian power in HOI4 and a crucial member of the Axis. Driven by Imperialist aspirations and a perceived sense of mistreatment by the West, Japan is primed to assert its dominance. In this article, we will delve into Japan’s strategic position, exploring how it can bolster its might for an impending war, and ultimately, how to elevate Japan to not only regional supremacy but a global powerhouse in HOI4.

Japan Starting Position in HOI4

After a strong modernization push in the Meiji era and the subsequent First Sino-Japanese and Russo-Japanese wars, Japan has cemented its place as one of the world’s global power and the only non-European nation (apart from the United States) to do so.

But beneath the surface, indignance boils with the perceived lesser treatment of Japan by the Western powers (especially after the Racial Equality Treaty).

With the interwar years leading to years of failed civilian governments, militarism has managed to take root in Japanese politics and firmly establish itself as the guiding principle for the Empire to take.

Armed with ambitions of taking on much of Asia under the banner of the Greater East Asian Co-Prosperity Sphere, Japan finds itself on the precipice of war, especially following the taking of both Manchukuo and Mengkukuo as vassal states in HOI4.

The Empire stands ready to push through all that stands within its path of Divine destiny, no matter their size or distance.

Initial Economic Position

Being an island nation, Japan’s lack of important resources such as rubber and oil historically fueled its thirst for new conquests and this is very much the same reflection here with Japan mainly producing steel, chromium, and tungsten.

Although Japan has 19 oil in the 1936 HOI4 start, 16 units of these are being imported from the United States, making any sanctions from them or the other allied powers devastating.

In terms of law, Japan has Limited Exports and Partial Mobilization for its trade law and economy law in HOI4, respectively. This is very much in line with other Axis powers at the time as these nations clamp down on allowing their resources to reach other nations while also preparing their industry for an upcoming war.

For national spirits, Japan has Zaibatsu and Militarism affecting the economy with the former giving bonuses to the military factory, civilian factory, and naval dockyard construction speed by 5% each at the expense of a higher cost for changing economy and trade laws.

Sadly, the latter has more or less negated the civilian factory bonus speed of the former as Militarism brings up the civilian factory construction speed time by 10% and also reduces the research speed by 5%.

Initial Political Position

As Japan has fully transitioned to an effective militaristic government and society, this is very much evident in the national spirit of Militarism which grants 20% bonus war support, a reduction of 20% in the justify war goal time, and 25% less cost to change the conscription law in HOI4.

Having Hirohito as the country’s leader places Japan in an extremely stable position with the Emperor’s trait, Emperor Showa, giving a whopping 60% bonus to stability.

Likewise, the Imperial Sanction trait increases the tension limit against the Chinese by 75%. Lastly, his Warrior Code makes the AI version of him unlikely to call allies into wars as it is believed that the spoils of war should only be theirs alone.

Japan doesn’t have much in terms of political advisors in HOI4, being a product of the earlier Hearts of Iron period. Some of their best advisors currently are Mitsumasa Yonai (Silent Workhorse), Hiroshi Oshima (Prince of Terror), and Takuo Gudo (War Industrialist).

In total, there are only 8 possible advisors for Japan in HOI4 though some cannot be described as useful with two of them locked to other ideologies while Kingoro Hashimoto is not useful as his ability to increase the fascist support being utterly worthless as Japan already starts off as 100% fascist.

In terms of subjects, Japan has both Mengkukuo and Manchukuo as vassals in HOI4 while parts of China like East Hebei, Dalian, and Formosa are all owned by the Japanese Empire.

Initial Military Position

The Imperial Japanese Army starts with 60 divisions spread across the disparate Japanese Empire. The army’s composition is rather mixed most division templates unsuited for war either through their division template, experience, or strength which necessitates a reform of the Japanese forces in the near future, prior to any conflicts.

The Imperial Japanese Navy is the third strongest navy and lays claim as the dominant naval force in the Pacific, only rivaled by the United States Navy. While formidable in its own right, many of its ships are aging and will need to be modernized or replaced to have a change with confronting the United States Navy and the Royal Navy in the seas and oceans.

The Imperial Japanese Air Force possesses a lot of planes at the start of the game, however, many of these planes are assigned to carrier duties, leaving only 7 squadrons capable of supporting any army operations.

In terms of leadership, the Japanese have a good number of choices for military appointments such as Hitoshi Imamura (Army Logistics), Yasuji Okamura (Infantry), Chuichi Nagumo (Carriers), Nishizo Tsukahara (Naval Strike), Mitsuo Fuchida (Tactical Bombing), Prince Fushimi Hiroyasu (Naval Aviation), and Isoroku Yamamoto (Naval Aviation Pioneer) himself to name a few.

Interservice Rivalry

Unique to Japan is the bitter rivalry between the Army and the Navy for the allocation of resources and the overall strategy in the Pacific. This is reflected in HOI4 with the national spirit of Interservice Rivalry and the decisions as to which service to prioritize.

The balance of power starts off as balanced but should it tip to either side, the service leading will get a bonus at the expense of its rival.

However, in light of Japan’s strengths, these are the best decisions to take:

  • Prioritizing Steel – The Army comes out on top since the early game is all about taking China and rebuilding the Army.
  • Prioritizing Aircraft Construction – The Navy wins out since a strong carrier force is needed to confront the Americans and their naval industry.
  • Prioritizing Conscription or Draft Exemptions – Draft Exemptions are better since the recruitable population is already not needed with Japan’s many national spirits increasing the recruitable population already (if China is a puppet, then even more reason).
  • Prioritizing Special Forces – Neither look well but the Naval barely wins due to their bonus in attack and defense but there is no need to take this decision if it can be avoided.

In all scenarios, it would be best to favor the Army in the early game while the 1940s should see the navy strengthened instead as by this time, the Allies will be our target.

The Better Historical Route for Japan in HOI4

This HOI4 path will see Japan following the same route it did historically where the Kodoha faction was purged and the Toseha faction emerge as the ultimate victor of the two.

In this HOI4 route, Japan will look to conquer China and bear its fangs against the Allies, seeking to best the British and American in a decisive naval encounter that will allow its courageous forces to force their surrender and establish the Greater East Asian Co-Prosperity Sphere as the only faction in Asia and beyond.

Opening Army Moves

Given that China will be our early target, it’s best to assign an army of 24 divisions on the Chinese front within East Hebei and then assign another army of 24 divisions to take Shanghai and let your final army of 12 divisions land in Fujian.

Be sure that two naval invasions are given (though with no divisions assigned) since that’s our limit for the meantime. While this is being done, train 12 more Hohei Shidan divisions and assign it to our final army to bring it to full strength.

For military leaders, assign Shunroku Hata as your Field Marshal while the armies should have Tomoyuki Yamashita head the force directly facing Beijing while the second army should be led by Hitoshi Imamura to give him more XP.

The last choice is up to the player though a personal preference would be to go for better logistics generals since China is a supply hell.

Start having all the forces exercise until they reach enough XP to become a regular unit. If you have enough XP, start reducing the Hohei Shidan to the default 6 infantry battalions and 2 artillery battalions. Convert all units for now to this division template as light tanks are not fully effective while trucks are more needed as supply vehicles.

For military factories, try to allocate the following:

  • 2 military factories for Infantry Equipment
  • 3 military factories for Support Equipment
  • 6 military factories for Artillery Equipment
  • A military factory each for civilian trains, trucks, basic carrier naval bombers, and basic carrier fighters. 

For the land doctrine, be sure to switch to Superior Firepower as it is the better land doctrine for all-around purposes.

Opening Navy Moves

Given that Japan is a dominant naval power in HOI4, it’s only fitting for the Navy to receive its own little guide separate from the Army. As Japan is producing already a new set of ships to complement its already notable fleet, we should trim them down to focus on building convoys and new ships.

Cancel the Kongo battleship, Zuiho carrier, Mogami cruiser, and Okonoshima cruiser, then set all other production lines to only a single ship. After this, start building convoys (at least 300-500 units) while we wait for new technologies to be researched.

For High Command, Chuichi Nagumo is the only worth addition to the list while there is no doubt that Prince Fushimi Hiroyasu should be the Chief of Navy. Yamamoto as the Theorist should round out the trio perfectly well as the Navy will take a backseat to the Army in the meantime.

At the start of the game, the Japanese Navy will square off against the Dutch East Indies fleet and establish naval dominance over the area which means that the South China Sea and the Straits of Malacca will be Japanese-dominated.

We’ll also be going with a ‘hack’ of sorts as once the convoys are complete, we’ll start building cheap carriers with the express purpose of refitting them once the latest technologies are complete. To this end, take the Sasebo Naval Arsenal design company to reduce production costs significantly. 

For the cheap carrier, basically, remove the anti-air and anti-ship modules on the Soryu class and build enough to bring the total amount of carriers to 8 (or even 12 if you’re daring enough).

Opening Economic Moves

Start by building 2 civilian factories in Kyushu, Chugoku, Kansai, Tokai, and Kanto since they have the highest infrastructure level on the mainland. Since Kyushu has only a single available building slot, construct 3 civilian factories in Tokai instead.

Research the following to start off: Basic Machine ToolsConstruction IElectronical Mechanical Engineering, and Passive Sonars (to counteract the American submarines).

When the researches are complete, continue the naval tree by researching 1936 Destroyer HullActive SonarBracket Shooting, and adding a touch of Radio to complete the mix.

Trade for whichever resources you require since the Army requires a heavy investment on its part.

Opening Political Moves

To start, justify a war against the Dutch East Indies as soon as possible. We’ll be conquering (or at the very least, occupying) their oil and rubber-rich areas to fund our war effort and the construction of planes in the future.

To begin the national focus tree, take the Purge the Kodoha focus. For the first political appointment, go for Mitsumasa Yonai for extra political power. He’s the only worthy pick at the start with the rest not being of great use.

Move at least 10 divisions of the third army to Taiwan and set them on a naval invasion of the Dutch East Indies province of Kalimantan as the first target. Position Yamamoto’s fleet in the same province as well and divide the task force equally into 4 fleets with the naval invasion support mission in the South China Sea, Celebes Sea, and Java Sea.

After the first focus, continue down to the Guide the Zaibatsus and National Mobilization Law. By this point, war will be possible with the Dutch East Indies and as such, we should launch an attack while the world tension is still low.

Take Kalimantan and then use the newly acquired naval bases to launch a final assault on Java and Sumatra to finally make the Dutch East Indies government surrender.

Unfortunately, we cannot move any troops to the Netherlands but we’ll let our German friends handle them later on. Focus on improving relations with Germany till it reaches the maximum possible.

The Prelude to China

Once the Dutch East Indies campaign ended, place the third army back to Taiwan and set two naval invasion orders, one for the second army towards Shanghai and one for the third army towards Fujian. Both naval invasion orders should only have 5 divisions each since 10 is our max at the moment.

Follow the focus tree to National Research SlotNationalize War IndustryNational Defense StateSpiritual Mobilization, and Liaison Conference. The downside to recruitable population following the move to a total war economy should be countered easily by the Spiritual Mobilization national spirit.

When research is complete, focus on getting the latest industrial, naval, and army research. Try to keep 2 on the industry, 2 on the army, and 1 on the navy in the meantime (when the National Research Slot focus has been completed).

For the next set of political appointments, go for Sasebo Naval Arsenal for the naval design company, Prince Kan’in Kotohito for the Chief of the Army, and Yasuji Okamura for a slot in the Military High Command.

When the focuses are complete once again, go for the Greater East-Asian Co-Prosperity Sphere and Marco Polo Bridge Incident to finally provoke a war with China. Like the Soviet Union, we cannot let the Chinese get rid of their debuffs before starting a war, hence the necessity of an immediate war.

The Second Sino-Japanese War

Once the focus Marco Polo Bridge Incident completes, we should be able to have our war with China. At this point, all armies should have stopped their training and have been ready with battle plans for the first army and complete naval invasion orders for the second and third armies.

Let the navy once again play a naval support invasion role in the Yellow Sea and the East China Sea. Once all armies have landed, set the navy to exercise once more to bring the XP higher.

Be sure to have all armies’ supply vehicles be motorized instead of horses as China’s large landscape makes the latter extremely detrimental to our campaign.

When the war starts, have only the first army’s order activated. When the Chinese have moved much of their force to defend their capital, let the naval invasions land in Shanghai and Fujian and immediately have all the other forces of each subsequent army join their comrades on the beachfront.

Set the second army directly against the Beijing forces to encircle them while the third army focuses on capturing the southern and central provinces of China.

Should any other Chinese faction join, this should not be an issue due to their armies likely being understrength or technologically disadvantaged. At no point should you call your puppet into the war since it will only open an unnecessary new front for the troops to handle.

Continue pushing the Chinese who should not have the capabilities to oppose your troops. If logistics becomes an issue further, appoint Hitoshi Imamura to your high command (though you could do this early if you have enough PP and CP) and get Logistical Focus as your Spirit of Division Command.

Post China

Assuming China and its allies have surrendered, we have the option of either annexing or puppeting China. The best suggestion here is to annex all coastal provinces and then set China as a puppet via the peace conference demands tree.

Alternately, you could give the remaining province to Manchukuo but due to the nation’s possibility of rebelling, it may not be a wise idea.

Since the war with China has ended, we will need to start redirecting the balance of power to the Navy. At this point, the following focuses should have been completed or should be next in line to be completed.

  • Sign Tripartite Pact
  • Strike South Doctrine
  • Army Expansion Law
  • Army Expansion
  • Supremacy of Will
  • New Naval Estimates

Create a heavy cruiser design with all its weapon modules containing light attack guns and a destroyer design with its only weapon module being a single torpedo turret. Keep building these two on repeat once the carriers and convoys are completed.

For research, keep focusing on industry (Dispersed Industry is great for Japan in HOI4 due to them nearly reaching the limit in building slots per state and Refinery/Oil Production for obvious reasons), 1940 carrier hull, 1940 destroyer hull, and continued naval research.

With enough political power, assign recommended naval personnel to their respective positions. Train three or four more full armies with the Hohei Shidan. You can add to their battalions to bring the combat width to 25 and start preparing them for motorization and mechanization once enough equipment has been built.

Sharpening our Fangs

The main goal of the 1940s is to get ready for the American conflict and to this end, The Zero focus must be completed quickly to unlock the Zero, which will be our main fighter as its superiority to the American design will make short work of them.

If all carriers are built already, switch the naval designer to Yokusaka Naval Arsenal instead and redesign the existing carrier designs to include the extra deck size and retrofit the cheaper ones to the latest design as this is much faster than simply building a new one out of scratch.

Complete the retrofit on all major ships and then set them back on exercising to build our XP further and bring the experience on each ship higher. Be sure to fill all carrier decks with mostly naval bombers as they’ll serve as the hammer of our forces against the enemy vessels. The remaining space should be occupied by carrier-focused zeroes.

When civilian factories reach 50, we can dedicate our focus to naval dockyards and military factories. Continue allocating equipment to the Army and assign a small force to invade Hawaii from the Marshall Islands.

Be sure to only be building Zeroes and CAS planes once the army requirements are met as these two planes will form the hard-punching artillery for our army once it lands on American soil.

At this point, we should have two carrier forces each consisting of 4 of our latest carriers and equal amounts of cruisers, destroyers, and our outdated fleet. We should already have completed the second naval transport research here so we can have multiple naval invasions in addition to our Hawaii force.

The Second World War

Target Singapore and the Philippines via naval invasion since we do not wish to bring Siam or any puppets into the fight for now. Papua New Guinea and North Borneo can be taken by troops coming in from the land border so no naval invasion is needed at the moment.

At this point, the global conflict should be in place. Before joining the war via an attack on the Philippines, be sure to have your navies in place to support the naval invasions of both Hawaii and Singapore.

Use your latest carrier fleet for each invasion as hopefully with our continued focus on naval research and superior technology, the outdated Allied fleet will be destroyed.

Assuming the naval battle has gone our war, we should use an entire army from Hawaii to launch an invasion of the American heartland in Los Angeles and San Diego. Set the navies to support a naval invasion once more and have a separate navy (at least 16 destroyers in a task force) on convoy escort duties to accompany our undefended troops to the front line.

At this point, assign an entire army group to fill the lines in California while all forces on the ground there should try to extend the perimeter while remaining stable. Focus on taking airbases in a state with such a facility and building some immediately should there be none. Our Air Force will be the driving force behind the army’s swift attack on the States.

Australia and New Zealand are nice targets but if they remain loyal to the crown, their territories will be sparsely defended and won’t be that much of a threat to us although you can use some troops to mop up their victory points to force a capitulation.

The War in America

By this point of the guide, the war in America should be waging fiercely as the American muscle should be in full swing at this point. If need be, bring more troops from the mainland and let the Chinese manpower replace their presence on the border with India.

If enemy naval presence in the area has been significantly reduced, you can change Nagumo from the High Command to Mitsuo Fuchida instead since his bonus to ground attack will heavily benefit our CAS forces.

Keep an eye out on your supply points and micromanage when possible. Since we are finally at war with the states, we can look to change some of our units to motorized, mechanized, and armored units. Be sure to use the optimal design for each division type to get rid of this.

Add more planes assigned to your armies there and with enough effort and persistence, the Americans should be knocked out though be careful of the Canadians on your side since they’ll likely aid the Americans.

Once the war with America ends, it’s best to puppet them again much like China since the entire states will take up a lot of manpower away from us solely just to garrison them. But in the meantime, request garrison support from China since we cannot let this manpower drain continue forever.

The Mopping Up

With the loss of America, Canada should be easy picking for our experienced forces. Following said conquest, the United Kingdom should be the only remaining major on the Allied side.

If India is a major by this point, you should call upon your Chinese troops (utilizing your best division template) along Siam and Tibet and allow them to launch a three-prong assault towards Delhi.

Transfer the two main battlefleets from the Pacific to German bases in France (assuming they have conquered it by this point, which they usually have) and prepare a naval invasion for an army across the English Channel to Dover.

Confront the Royal Navy with our battle-hardened and technologically superior ships and score an easy victory since the British rely more on battleships than aircraft carriers, unlike the Americans.

Once an army lands on the English coast, it should be easy picking from then on and the spoils of war can finally begin. Take whichever territory you prefer though having the United States as your puppet is preferable to occupation.

The Post-War

Assuming the war with the Soviet Union and Germany hadn’t ended, Japan has the ability to end the non-aggression pact with the Soviets in HOI4 and strike from Siberia.

Alternatively, Japan could detach from Germany and look to strike the Germans while they are busy with the Soviets then deal with the Soviets on their own (who would have likely taken millions of casualties by this point).

Like all other HOI4 post-war content, Japan is free to impose its will wherever possible as its army and navy are dominant in all theaters.


And that is all you need to know about how to play as Japan in HOI4. Check out other interesting HOI4 guides and articles:

Based in Santa Rosa, Philippines, Jonathan Ledesma is a Freelance Writer for Raider King.
Jonathan Ledesma
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