One of the most impactful ships in the Second World War were the Carriers. These giant floating islands work as a landing and take-off point for planes, which can move around on the sea, allowing them to perform effective missions in enemy territories.

Carriers are the bread and butter of the United States since they can’t really use their planes on the Pacific front otherwise.

Recommended Read: How to Increase Supply in HOI4

They are also vital for naval-focused countries like the United Kingdom and Japan for their continuous use of naval invasions.

These ships are also very important in naval battles since they allow the powerful bombers that deploy off of them to deal massive damage to enemy fleets.

To put planes on Carriers in Hearts of Iron 4, you need to leave them out of combat manually where you want them to. Then, you can deploy your planes on them, as you would on any normal airfield.

Table of Contents

• How to Put Planes on Carriers in HOI4
• How Carriers Work and How to Use Them

How to Put Planes on Carriers in HOI4

You can’t just throw any plane on a carrier! You must first research the land-based version of an aircraft. Then, you’ll need to research the carrier-capable versions of Fighters, Close Air Support, and Naval Bombers.

These variants have different names, stats, and artwork compared to their land-based counterparts. You’ll find the research option by clicking the aircraft carrier button on the aircraft type in the air research tab.

When you build a new carrier, it comes with a pre-assembled air wing produced during construction using your dockyards.

This air wing will be equipped with the most up-to-date carrier-capable models you’ve researched. Before launching the carrier, you can adjust the types of planes included in its air wing to fit your strategy.

When your carrier joins a patrolling fleet, its air wing automatically transforms into a Carrier Air Group. This Carrier Air Group automatically engages in any naval combat your fleet encounters.

How Carriers Work and How to Use Them

Carriers can do two things in HOI4:

• Carriers act as floating air bases for carrier-capable aircraft (fighters, CAS, and naval bombers). These planes can be launched for various missions outside of combat.
• During combat, carriers deploy their aircraft as a Carrier Air Group, automatically engaging enemy fleets. They don’t require the usual 8-hour wait to join the fight.

Carriers function as mobile airfields. The number of planes they can carry depends on the available hangar space. This allows for incredible strategic flexibility. You can equip your carriers with:

• Naval Bombers: Deliver devastating blows to enemy fleets, particularly effective against capital ships.
• Fighters: Provide crucial air defense against enemy carrier aircraft, safeguarding your fleet from aerial assaults.
• Close Air Support (CAS): Offer offensive support for land forces during amphibious assaults or naval invasions. By strategically positioning your carriers near the invasion zone, you can provide crucial air cover for your landing troops.

How to Design a Carrier

The design of the Carrier can be very important, since this allows you to get the most out of this huge, heavy ship.

Carriers are very vulnerable, so focus on maximizing their hangar space to carry more planes. Heavy armor is a waste. Rely on your escorts for protection. If your frontline screen is gone, your carriers are likely doomed anyway.

Match your carrier’s engine speed to your fleet’s overall speed. Carriers are often faster than battleships. Secondary weapons are a personal choice, offering some light attack against destroyers.

Tips on How to Use Them

• Before engaging enemy fleets, consider swapping any carrier CAS for naval bombers. This maximizes your damage output.
• Strive for a balance between offense and defense. A common strategy is using 1 fighter for every 5 naval bombers. Fighters protect against enemy carrier aircraft, while bombers deal heavy damage with their piercing attacks.
• Carriers are vulnerable once their escorts are destroyed.
• Unlike land-based aircraft, carrier wings can be trained and require micromanagement for optimal performance.

That’s everything you need to know about how to put planes on carriers in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

In Hearts of Iron 4, your biggest enemy will more often than not be Supply. As soon as you see that annoying red supply bag above your troops, you will start seeing real hits to your equipment and Manpower pool.

To stop this useless loss of resources, you will need to somehow increase the Supply in those provinces.

Recommended Read: Best Air Doctrine in HOI4

Most players don’t really understand how Supply works, which is why they often fail to provide enough of it for their dying troops.

There are a few ways to increase Supply in Hearts of Iron 4, and those are to increase Motorization levels, build new Supply Hubs, build Railways connecting Hubs, and to improve Infrastructure.

Table of Contents

• How Supply Works
• How to Increase Supply in HOI4

How Supply Works

Supplies aren’t physical items you build. Instead, they’re a resource automatically generated in your states based on factors like population, infrastructure, victory points, and how well-connected they are.

Each division has a “supply appetite.” They need a certain amount of supply to function effectively. If they don’t get enough, their organization suffers, making them easier to defeat.

There are two ways your troops get their supplies:

• State Supply – This comes directly from the province itself based on population, infrastructure, and victory points. Think of it as the local food stores and farms keeping your troops fed.
• Hub Supply – This comes from a network of supply hubs connected to your capital. Think of these hubs as regional distribution centers sending supplies to your troops on the front lines.

Your capital acts as the main supply hub, sending supplies to other hubs via railways. The maximum amount of supply your capital hub can handle depends on the number of factories you have. It’s like a giant warehouse with limited space.

This capital supply cap doesn’t directly dictate how much reaches all your hubs. It’s just a total limit. Each individual hub also has its own maximum supply level based on the quality of the railway connecting it to the capital.

Beginner Explanation

So, imagine your capital as a giant supply depot. It has a limited capacity, the Supply Cap, based on your factories. This cap represents the total amount of supplies it can hold and distribute.

Now, you connect this central depot to other smaller depots called Supply Hubs using railways. These hubs act like regional distributors, sending supplies to your troops. Here’s the catch:

• The maximum supply a Hub can provide depends on the railway quality connecting it to the capital. Better railways mean higher supply flow!
• This Hub’s supply capacity is either based on the capital’s Supply Cap or the railway level, whichever is lower. Think of it as a bottleneck.
• The Hub then distributes supplies to nearby troops. If the total amount of supplies needed by these troops is greater than the Hub’s cap, they won’t get enough.

Railways only connect hubs to the capital, they don’t directly supply troops. Building a railway to a province with no supply won’t magically create some!

By keeping your capital’s Supply Cap high (more factories) and upgrading railways, you ensure your troops get the supplies they need to win!

How to Increase Supply in HOI4

There are four ways to increase Supply in a state or province in HOI4:

• Increase Motorization Level
• Increase Railway Level
• Build Supply Hubs
• Increase Infrastructure Level

Increase Motorization Levels

Every Supply Hub in HOI4 has a limited range for supplying troops. This range depends on your chosen Motorization Level, which essentially determines whether you use trucks or horses for deliveries.

Motorization Levels:

• Horse (Default): This is the standard option at game start for both Hubs and armies. It has a short range but requires minimal resources. Great for early game when trucks might be scarce.
• Trucks: Upgrading to trucks increases the Hub’s supply reach and the amount of supplies it can deliver to existing provinces. However, you’ll need to dedicate trucks in your Logistics to keep this supply flowing.
• Many Trucks: This doubles the range and supply of the “Trucks” level, but also uses twice the amount of trucks.

There are two ways to leverage Motorization Levels for better supply:

• Individual Hub Control: Click on a Supply Hub in the Supply Map Mode. You’ll see three bubbles on the right. The rightmost one represents Motorization Level. Click it to switch between Horse, Trucks, and Many Trucks.
• Army-Wide Priority: Set a global preference for all your armies. Select an army or army group, then click the “horse button” above its weight (the boat icon) to adjust the Motorization Priority. Be careful though, prioritizing trucks for all armies can strain your economy if you’re not prepared.

By choosing the right Motorization Level, you can ensure your troops receive the supplies they need, no matter where they are on the battlefield.

Increase Railway Levels

The maximum supply a Hub can provide (its cap) depends on the quality of the railways connecting it to your capital. This can become a problem if you have too many divisions stationed near a Hub, causing it to reach its capacity.

You can increase the supply capacity by improving the railways between the Hub and your capital. Here’s how to do it easily:

1. Open the Supply Map Mode and click on the affected Supply Hub.
2. Look for the button labeled “Upgrade Bottlenecks” in the middle.
3. Clicking this button will automatically optimize the railways connecting the Hub to the capital. This can involve either:
   • Eliminating bottlenecks – Ensuring all railway segments between the Hub and capital are at the same level, removing any bottlenecks that restrict flow.
   • Upgrading the entire line – If all segments are already the same level, the button will upgrade them all to a higher level, increasing the overall supply capacity.

If you conquer a new Supply Hub and it lacks supply, the most likely culprit is a missing connection.

Simply build a railway from the Hub to any existing railway line in your territory. This will integrate the Hub into your supply network.

Build Supply Hubs

A common challenge you’ll face is the vast distance between existing Supply Hubs. This creates gaps in your supply coverage, leaving some areas underserved. To solve this, you will need to build new Supply Hubs.

However, constructing Hubs is a heavily time-consuming process. In the base game, it can take a significant amount of time to complete just one.

To counter this, consider prioritizing the construction of essential Supply Hubs at the beginning of the game. This proactive approach ensures your troops have the coverage they need from the outset.

Many countries have access to a national focus called “Reorganize the Railway System.” Completing this focus significantly speeds up the construction of Supply Hubs, allowing you to build them three times faster.

By strategically placing new Hubs and taking advantage of this decision, you can ensure your troops have a reliable supply chain, even in remote areas.

Increase Infrastructure Levels

Even with a well-developed network of Hubs and railways, sometimes you might need an extra supply nudge in specific regions. This is where Infrastructure comes in.

Building Infrastructure in states facing supply issues provides a small but helpful bonus. Each level of Infrastructure adds 0.3 Supply to all provinces within that state, reaching a maximum of 1.5 Supply at the highest level.

This bonus is fantastic because it’s “free” supply, not relying on Hubs or railways. It’s also used first, before supplies from Hubs, ensuring your troops get this local boost first.

Essentially, well-developed infrastructure acts as a local supply buffer, reducing the burden on your Hubs and ensuring your troops have a reliable baseline supply.

This can be particularly helpful in remote areas or during the early game when Hub construction might be limited.

That’s everything you need to know about how to increase Supply in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

Doctrines are the part of Heart of Iron 4 that cause the most debates. Since you will always have to choose only one out of 3 or 4, players get really heated about which one is actually the most useful.

Most of the time, the right answer is: “the doctrine that fits your needs.” This is generally the right answer for air doctrines as well since the bonuses are very good no matter which doctrine you choose, as opposed to the land doctrines, where you should never pick Mass Assault.

Recommended Read: Hearts of Iron 4 – Warfare Guide

The first thing you will need to ask yourself is where are you willing to be weaker and what exactly do you want to gain from using your air force.

In this guide, we will go through all of the air doctrines in Hearts of Iron 4, explain why each one of them is very useful, and why, most of the time, Operational Integrity is the best one to choose.

Table of Contents

• What Each Air Doctrine Does
• What Is the Best Air Doctrine in Hearts of Iron 4?
• Recommended Air Doctrine Per Country

What Each Air Doctrine Does

There are three air doctrines in HOI4:

• Strategic Destruction
• Battlefield Support
• Operational Integrity

Generally, all doctrines offer very similar bonuses, which is why you can’t really go wrong here. There are only a few bonuses that are different, and those can make a big difference.

Here are all the bonuses that you get by investing in any of the air doctrines, that you will receive no matter which path you go down:

• Air Superiority: +15%
• Fighter Detection: +10%
• Ground Support: +10%
• Interception Detection: +10%
• Naval Mission Efficiency: +10%

Strategic Destruction

As explained by the developers under the doctrine, Strategic Destruction is the go-to doctrine for people that want to destroy their enemies’ provinces using Strategic Bombers.

There are two choices you will have to make down this path, where you will first have to choose between better Fighter skills in Interception or Air Superiority missions, and then choose between a big flat bonus to Strat Bombing or a smaller one with a decreased night debuff.

Usually, if your goal is to bomb your enemies to hell, this is the right doctrine to choose.

Here are the exact bonuses you can get down this doctrine, ignoring the general ones we listed above:

• Air Superiority: +15%
• Bomber Defense: +25%
• Escort Efficiency: +25% & Strategic Bombing: +50% / +40% & Night Time Strategic Bombing Penalty: -50%
• Fighter Agility: +10%
• Interception Mission Efficiency: +20% / Air Superiority Mission Efficiency: +20%
• Naval Mission Efficiency: +5%

Battlefield Support

This is the doctrine to buff your CAS and deal crazy damage to the land troops below your air force. Or, at least, that’s how it’s described. If you actually look at the buffs, your CAS do become more powerful, but not enough to make a huge difference.

It does feel, however, that you are dealing huge damage to the troops on the ground, as long as you’ve got Air Superiority.

Here are the exact bonuses you can get down this doctrine, ignoring the general ones we listed above:

• Air Superiority: +15%
• Air Superiority Mission Efficiency: +15% / Ace Generation Chance: + 25%
• Air Support Mission Efficiency: +40%
• CAS Agility: +20%
• Fighter Detection: +5%
• Ground Support: +30%
• Interception Detection: +5%
• Strategic Bombing: +15%
• Tactical Bomber Strategic Bombing: +10%

Operational Integrity

Weirdly enough, the Operational Integrity doctrine is described as the tactical bomber doctrine since it’s got a single Strategic Bombing boost for tactical bombers.

However, analyzing the doctrine better will likely make you realize that this is actually the best doctrine for fighters.

Most players in HOI4 want to make their fighters better than their enemies’, since this is the way you will win the aerial battles and gain the Air Supremacy needed to also get that intense CAS damage.

Operational Integrity gives you exactly what you need to effectively win in the air and get that Air Supremacy you clearly want over your land troops.

Here are the exact bonuses you can get down this doctrine, ignoring the general ones we listed above:

• Ace Generation Chance: +20%
• Air Superiority Mission Efficiency: +20%
• Bomber Defense: +20%
• Fighter Agility: +10%
• Fighter Detection: +10%
• Interception Detection: +10%
• Interception Mission Efficiency: +20%
• Strategic Bombing Visibility: -50%
• Tactical Bomber Strategic Bombing: +20%

What Everything Means

Here’s a brief description of all the bonuses you can get with these doctrines so you can understand exactly what they do:

• Ace Generation Chance: Increase the probability of generating aces during missions.
• Air Superiority Mission Efficiency: Improves air attack, air defense, and agility for planes on this mission.
• Air Support Mission Efficiency: Improves air attack, air defense, and agility for planes on this mission.
• Bomber Defense: Increases the air defense for planes on Strategic Bombing mission. 
• Enemy Air Support: Modifies the negative effect enemy air superiority has on the combat ability of our ground troops.
• Escort Efficiency: Reduces disruption from enemy attacks.
• Fighter Detection: Increases the amount of detection planes on Air Superiority mission contribute to the region.
• Ground Support: Increases the scaling rate of the Enemy Air Support bonus provided by air superiority
• Interception Detection: Increases the amount of detection planes on Interception mission contribute to the region.
• Interception Mission Efficiency: Improves air attack, air defense, and agility for planes on this mission.
• Naval Mission Efficiency: Improves air attack, air defense, and agility for planes on this mission.
• Night-time strategic bombing penalty: Reduces the negative effects of night for planes on Strategic Bombing mission, notably the Ground Bombing Targeting penalty.
• Strategic Bombing Visibility: Counteracts enemy detection when on Strategic Bombing mission, reducing the maximum number of enemy planes responding to the bombers. 
• Strategic Bombing: Improves Strategic Bombing damage for planes on that mission.

What Is the Best Air Doctrine in Hearts of Iron 4?

Though all three doctrines are useful, depending on the country you select at the start, Operational Integrity will usually be your main choice for most countries, making it the best air doctrine in HOI4.

Most of the time, the most important thing in air battles is losing fewer fighters than your enemy. If you and your rivals place all of your planes in one air region, destroying more of their fighters to get Air Superiority is the way to go.

At that point, it becomes an attrition battle, where you see which one of you can keep destroying more planes, as bombers and CAS also get destroyed in the process. For this reason, Operational Integrity is the main doctrine to go for if you play as any minor country.

Since you don’t have the capabilities to build a large air force, your goal is to just keep your skies safe, to avoid the total destruction that CAS deal or the annoying Civ factory usage that bombers cause by leveling your country.

So, to avoid most problems, you just need to pick the Operational Integrity doctrine and send your fighters to fight. The Fighter Detection bonus, combined with Ace Generation and Fighter Agility, will make you the biggest power in the air.

71Cloak has made a video where he made nations fight with the same number of fighters and same tech, using different doctrines.

He pit Strategic Destruction against Battlefield Support, Battlefield Support against Operational Integrity, and Strategic Destruction against Operational Integrity.

In all scenarios, Operational Integrity lost 10 to 20% less fighters in the battles against the other doctrines, making it the superior choice for Air Superiority.

Which Countries Should Choose Strategic Destruction

Though Operational Integrity is the best choice for most countries, this does not mean you need to pick it. As you’ve seen from the stats, you just lose more fighters in the air battles, but this does not mean you lose if you have bigger production pools.

So, if you can afford to lose fighters and don’t care about losing more than your enemy, then you can pick one of the other two doctrines. This is usually the better choice for major countries that have huge production capabilities and can afford to lose thousands of planes.

Countries like the United Kingdom and the USA should always complete the Strategic Destruction doctrine, since they spend most of their time away from the fighting.

They also have amazing industries, allowing them to pump out as many fighters as it is necessary.

Destroying Germany’s industry is very important in taking them down, and the Strategic Destruction doctrine will help out a lot on this front.

This doctrine is also very useful for Commonwealth nations that won’t really be very involved in the fighting on the ground, but that can constantly pester Germany by bombing various different parts of Europe in hopes of destabilizing the country.

Most of America should choose this doctrine, unless they plan on attacking their neighbors. However, in most cases, even if you do attack your neighbors, Supply will be your biggest enemy, not air forces.

Which Countries Should Choose Battlefield Support

If you spend most of your time in huge land battles with your enemies, then Battlefield Support is a really good choice.

Though CAS deals a ton of damage even without this doctrine, this one allows you to quickly push through enemy lines with its amazing prowess.

A country like Germany, the USSR, and Japan would profit a lot from Battlefield Support, since all of them have to win their land battles first and foremost.

The only problem is that Battlefield Support gets the worst fighter bonuses out of the bunch, so you’ll always lose more planes than your enemies.

This doctrine will usually only be useful if you have a giant air force that doesn’t mind losing a lot, in exchange for huge wins on land. Or, if you have a really good fighter design, then you shouldn’t really be afraid of the air battles and just concentrate on destroying divisions.

Battlefield Support will make sure that the ground troops truly suffer if you’ve managed to gain Air Superiority, which should be easily done against the AI with enough research into Fighter and a design that focuses on Agility and damage.

Recommended Air Doctrine Per Country

Here are the best air doctrines to choose for each country in HOI4:

• Afghanistan: Operational Integrity
• Albania: Operational Integrity
• Argentina: Operational Integrity
• Sultanate of Aussa: Operational Integrity
• Australia: Strategic Destruction
• Austria: Operational Integrity
• Belgium: Strategic Destruction
• Bhutan: Operational Integrity
• Bolivian Republic: Operational Integrity
• Second Brazilian Republic: Operational Integrity
• British Malaya: Strategic Destruction
• British Raj: Operational Integrity
• Bulgaria: Operational Integrity
• Dominion of Canada: Strategic Destruction
• Chile: Operational Integrity
• China: Operational Integrity
• Colombia: Operational Integrity
• Communist China: Operational Integrity
• Costa Rica: Operational Integrity
• Cuba: Operational Integrity
• Czechoslovakia: Operational Integrity
• Denmark: Operational Integrity
• Dominican Republic: Operational Integrity
• Dutch East Indies: Operational Integrity
• Ecuador: Operational Integrity
• El Salvador: Operational Integrity
• Estonia: Operational Integrity
• Ethiopia: Operational Integrity
• Finland: Operational Integrity
• France: Strategic Destruction
• Germany: Battlefield Support
• Kingdom of Greece: Operational Integrity
• Guangxi Clique: Operational Integrity
• Guatemala: Operational Integrity
• Haiti: Operational Integrity
• Honduras: Operational Integrity
• Kingdom of Hungary
• Iceland: Operational Integrity
• Iran: Operational Integrity
• Iraq: Operational Integrity
• Ireland: Strategic Destruction
• Italy: Battlefield Support
• Japan: Battlefield Support
• Latvia: Operational Integrity
• Liberia: Operational Integrity
• Lithuania: Operational Integrity
• Luxembourg: Operational Integrity
• Manchukuo: Operational Integrity
• Mengkukuo: Operational Integrity
• Mexico: Strategic Destruction
• Mongolia: Operational Integrity
• Nepal: Operational Integrity
• Netherlands: Strategic Destruction
• New Zealand: Strategic Destruction
• Nicaragua: Operational Integrity
• Norway: Operational Integrity
• Oman: Operational Integrity
• Panama: Operational Integrity
• Republic of Paraguay: Operational Integrity
• Peru: Operational Integrity
• Philippines: Operational Integrity
• Poland: Operational Integrity
• Portugal: Operational Integrity
• Romania: Operational Integrity
• Saudi Arabia: Operational Integrity
• Shanxi: Operational Integrity
• Siam: Operational Integrity
• Sinkiang: Operational Integrity
• South Africa: Strategic Destruction
• Soviet Union: Battlefield Support
• Spain: Battlefield Support
• Sweden: Operational Integrity
• Switzerland: Operational Integrity
• Tannu Tuva: Operational Integrity
• Tibet: Operational Integrity
• Turkey: Operational Integrity
• United Kingdom: Strategic Destruction
• United States: Strategic Destruction
• Uruguay: Operational Integrity
• Venezuela: Operational Integrity
• Xibei San Ma: Operational Integrity
• Yemen: Operational Integrity
• Yugoslavia: Operational Integrity
• Yunnan: Operational Integrity

That’s everything you need to know about the best air doctrines in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

In Hearts of Iron 4, your main goal will be to win the Second World War. Unfortunately, it is quite hard to do this without doing some research beforehand, as the gameplay mechanics are very complicated for newcomers.

There are many moving parts when it comes to warfare in Hearts of Iron 4. You will need to know what most of the stats mean, how to design your divisions properly, and how to keep everyone supplied throughout the battles.

Recommended Read: How to Use Floating Harbor in HOI4

To properly win all your wars, you will need to master some of the tedious parts of micromanaging your troops, which are usually worth the effort.

In this guide we will show you everything you need to know about warfare in Hearts of Iron 4, ranging from how divisions work, to how to win every war you participate in.

Table of Contents

• How Divisions Work
• Combat Width
• Supply
• How to Win Wars in HOI4

How Divisions Work

Divisions are the bread and butter of war. They are your troops which you guide on the battlefield to win wars.

These divisions have two main stats that will decide their ability to fight properly and win:

• Strength (orange bar)
• Organization (green bar)

Strength is the closest thing to HP your divisions have. If a unit completely loses its Strength it will be destroyed, and you will lose whatever was left of it forever. The Strength is a combination between equipment and Manpower.

Organization is the morale of your division. If they lose all Organization when attacking, they will immediately stop their offensive.

If they lose all Organization when defending, the division will start retreating to a different province, in order to recover their Org.

Divisions with lower than maximum Strength or Organization are much easier to defeat and are usually your first sign either you or your enemy are starting to lose the war.

There’s no way to make sure your Strength is larger and all you can do to keep this stat high is to make sure you always have surplus equipment and Manpower to supply back to your divisions after battles.

For Organization, on the other hand, you personally decide how much max Organization you can have in the division designer

Division Designer

The division template designer is a huge part of the game. In the Recruit & Deploy menu players can edit their divisions, choosing exactly what battalions are part of it and what stats they actually have.

What All Division Stats Mean

In the division template designer, players will see three columns: Base Stats, Combat Stats, and Equipment Costs.

Under these columns, they can see the division composition, which will help figure out what bonuses the division will get from advisors and doctrines, and the Hardness percentage.

Base Stats

• Max Speed – the speed that the division will have. The minimum is 4 km/h, with everything above 10 being really fast.
• HP – number that represents how easy it is to destroy the division. The higher the number, the longer the division will last in a situation where it will likely disappear forever.
• Organization – the real health of a division. In battles, divisions lose if they lose all of their Organization. Once they retreat, they have to wait to recover before being at full strength.
• Recovery Rate – the speed at which Organization recovers out of combat.
• Reconnaissance – stat that decides if the general of the army will counter the tactic of the enemy. The total is a combination between the division’s stat and the one of the general.
• Suppression – efficiency when it comes to suppressing occupied territory. Stat only relevant for Garrisons.
• Weight – determines how many Convoys are needed for transport across water.
• Supply use – determines how much Supply the division needs in the province they are stationed.
• Reliability – how likely it is that equipment will break down due to attrition. A low Reliability will result in a lot of meaningless losses of equipment.
• Reliability Bonus – extra Reliability gained from Support Companies.
• Trickleback – returns a percentage of lost Manpower in battles to the country’s Manpower pool.
• Exp. Loss – determines the amount of division experience lost per Manpower lost.

Combat Stats

• Soft Attack – the main Attack stat. All units that have low Hardness (no tanks or armored divisions) take mainly Soft Attack damage.
• Hard Attack – the Attack stat for armored divisions. Units with higher Hardness take more Hard Attack damage.
• Air Attack – lowers damage taken from CAS by up to 75% and attacks planes above them.
• Defense – reduces damage that enemies deal to the division when defending.
• Breakthrough – reduces damage that enemies deal to the division when attacking.
• Armor – if Armor is higher than the attacking division’s Piercing, the defending division loses -50% less Organization and the attacking division loses +50% more Organization.
• Piercing – if Piercing is higher than the defending division’s Armor, the defending division loses +50% more Organization and the attacking division loses -50% less Organization.
• Initiative – increases reinforcement rate and Coordination. Relatively useless stat.
• Entrenchment – increases Max Entrenchment. Every point of Entrenchment gives a division +2% Defense and Soft Attack. Lose the bonus when moving.
• Eq. Capture Ratio – the amount of equipment the division captures during battles.
• Combat width – how much space the division takes on the battlefield. Check out our guide on Combat Width for more info.

How to Make Defensive and Attacking Divisions

When designing your divisions, there will only be a few stats that you should care about, depending on what you want to do with those divisions.

If you want to make defensive divisions that only need to hold back your enemies, then concentrate on Defense, Armor, and Entrenchment.

If you want to make attacking divisions, concentrate on Soft Attack, Hard Attack (if you’re fighting tanks), Breakthrough, and Piercing.

Hardness

There are two types of Attack in HOI4: Soft and Hard.

Soft Attack mainly targets divisions with low Hardness and Hard Attack hits divisions with high Hardness. Here is the exact formula that decides how a division is damaged in HOI4:

Attack = (1 – Hardness) * Soft Attack + Hardness * Hard Attack

Hardness is a stat that represents the number of armored battalions that are part of the division. Infantry has 0% Hardness, while Tanks have 100%.

A normal Infantry division will have less than 10% Hardness, while normal Armored divisions will have around 50% to 70%.

This means that an Infantry division with 0% Hardness won’t receive any of the Hard Attack damage, but 100% of the Soft Attack. A division with around 50% Hardness will receive half of both.

In singleplayer the AI generally uses only divisions with close to 0% Hardness, which means that Soft Attack is king. Generally aim to build divisions with really high Soft Attack to win most fights.

In multiplayer, most will focus on getting some Hardness on all divisions, with a lot of elite Tank divisions to push the lines while micromanaging.

To combat these, you will need a few Tank Destroyers to combat them with Hard Attack.

A single Tank Destroyer in most defensive divisions will usually be enough to also deal damage to the powerful Tank divisions that players use in multiplayer.

Combat Width

Combat Width in HOI4 is the amount of space that divisions can take up in a province battle.

Each province will have a set maximum Combat Width based on the terrain type (Plains, Urban, etc.), and each division will have its own Combat Width stat, which will decide how they fit in the battle.

When you create a division using the division designer, you will notice that most line battalions will add either 1, 2, or 3 Combat Width to your division, with most of them using 2 (Support Companies don’t add any Combat Width).

You can also check the Combat Width of a province before attacking by clicking on the tile and hovering over the image of the Province in the bottom left corner of the screen, which will tell you the terrain type and Combat Width.

When you start a battle, you can see if you open the fight menu (press the bubble with numbers in it) a number in the center that represents the Combat Width.

This can also change based on how many directions the province is attacked from (+half of the normal Combat Width per attack direction).

What Is the Best Combat Width?

When optimizing and designing your divisions in HOI4, you need to make sure that you choose the best Combat Width that will get the least amount of negative modifiers in most terrain types.

One problem that you can often bump into is making your divisions too small (less than 12 Combat Width) or too large (bigger than 40 Width), which will often either give you horrible Combat Width debuffs or just bad stats in the battle.

Taking this into consideration, the best Combat Width stats that you can use for your divisions in HOI4 are these:

• 14/15
• 18
• 24/25
• 35/36

Supply

Another thing that will decide if you can win battles or not is Supply. Supplies aren’t actually an item or equipment you can produce in the game.

Supplies are a resource that appears in your states based on various factors, such as state population, Infrastructure, Victory Points, and connection through Hubs.

All divisions in the game have a Supply consumption stat that decides how much Supply they need, which you should provide, otherwise their Organization will lower, making them easy to destroy.

There are two main sources of Supply in all provinces: State and Hubs.

The State Supply is the amount of Supply a province will get based on population, Infrastructure, and Victory Points. Supply from Hubs is the amount of Supply a province will get based on its connection to the capital.

The capital of your country has a main Supply Hub, the Capital Hub, that sends Supply to all the Hubs in the country through Railways.

The maximum amount of Capital Hub Supply (the Supply Cap) is based on the number of factories in the country.

This does not mean that the Supply Cap in your capital is how much supply you can send to all the Hubs. It is just a number that represents the maximum Supply you can have in all your Hubs.

Based on the Railway level, the other Supply Hubs have a maximum level of Supply they can provide as well.

How to Win Wars in HOI4

To actually win wars, you just need to plan everything better than your enemy.

If your divisions have good designs, they have Supply, and there are no huge debuffs against them, you shouldn’t have a lot of problems pushing through.

HOI4 is a numbers game, and having the bigger numbers will always allow you to win. Having huge Soft Attack, for example, is all you need to win in single player.

Putting a lot of Artillery in all of your divisions, even if they are Infantry divisions, is more than enough to win almost every fight.

A decent strategy is usually to allow the enemy to lose Manpower and equipment before pushing through. Trick your enemy into attacking and defend, losing almost nothing while they lose everything.

This strategy is usually the best way to win absolutely every war in the game, as the AI will usually throw troops at you until their Strength begins to waver. Once you notice that their Strength is below 70%, you should usually start pushing.

If you are playing as an offensive country, like Japan or Germany, then your main goal is capturing important cities. Build around speed and just push hard to get around the enemy line and get Victory Points.

Also, always look for encirclements. Even if you aren’t micromanaging and like just staring at your army as they push, help by creating encirclements.

Completely destroying enemy divisions is the way to win wars. This significantly lowers their Manpower and equipment, speeding up their capitulation.

That’s everything you need to know about how to win wars in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

Hearts of Iron 4 has a lot of hidden mechanics that most players have either never seen or never used. The Floating Harbor is one of these unique things that you can ask players with over one thousand hours about and still get confused answers.

Though the Floating Harbor isn’t one of the most useful pieces of equipment in the game, it is still something that can make a huge difference if you play your cards right.

Recommended Read: Hearts of Iron 4 – Navy Guide

The Floating Harbor is a special piece of equipment that acts as a Supply Hub when landing a Naval Invasion.

To use a Floating Harbor, you need to press the Naval Invasion Order (With Floating Harbor support) button that appears when you select an army and then just go through with a normal Naval Invasion. To press the button, you first need to build at least one Floating Harbor ship.

Table of Contents

• How to Unlock and Produce Floating Harbors
• What Is a Floating Harbor?
• How to Use the Floating Harbor in HOI4

How to Unlock and Produce Floating Harbors

Before we go into how to use the Floating Harbor, let’s first talk about how to actually get it.

First of all, you’ll need to complete the second naval transport research tech, the Landing Craft. This will improve the capacity for Naval Invasions while also unlocking the Floating Harbor.

Then, open up the Production menu and select to build ships. The Floating Harbor should be at the top, right below Convoys. Set up a production line for it, assign some Naval Dockyards, and wait for at least one to pump out.

What Is a Floating Harbor?

The Floating Harbor is a special ship in HOI4, only available with the No Step Back DLC, that can be used to initiate a special type of Naval Invasion order.

The Floating Harbor will deploy alongside the Naval Invasion, creating a Supply Hub where the troops landed.

This Floating Harbor Supply Hub will last for 30 days, during which your divisions will have full supply and can fight as long as they can, even though they lack a connection to a port or the capital of your country.

Once the 30 days have passed, the Floating Harbor will get destroyed and you will now have to reach a real hub or port to get supplies for the divisions.

How to Use the Floating Harbor in HOI4

To use a Floating Harbor in HOI4, you will need to select an army and press the button right next to the Naval Invasion order, which shows almost the same but has a chest on water sign with an arrow rather than an anchor with an arrow.

Do the exact same thing you would do when launching a naval invasion:

1. Left-click on the province where you want your troops to leave from.
2. Right-click on the enemy province where you want your troops to land.
3. Activate the execution of the plan.

The naval invasion won’t launch unless you have:

• 50% Naval Supremacy in all sea regions where the troops will have to navigate.
• Enough Convoys to carry the troops.
• Enough Naval Invasion Capacity.

Once everything is right, your troops will sail to reach their destination, fight enemy divisions, if there are any in the selected provinces, and land.

The Floating Harbor will be visible on the water, right next to the troops, and you can now see a Supply Hub on the map where a port would normally be.

Open the Supply mapmode to see the Floating Harbor Supply Hub and hover over it for more details. There is also a cheesy strategy that you can use to make the Floating Harbor last longer.

How to Prolong a Floating Harbor’s 30-day Timer

If you didn’t know this, you can actually send Naval Invasions in your own territories, as long as they are occupied provinces. This means that you can set up another Floating Harbor Naval Invasion in the territories you currently have your troops.

When those new divisions land alongside your other marines, the Floating Harbor Supply Hub’s 30-day timer will reset, allowing you another extra 30 days to keep your troops supplied.

The only thing that you will lose doing this is Floating Harbors, as you instantly lose one once a Naval Invasion Order with Floating Harbor support has been sent out to fight.

This is one of the best ways to attack countries in territories without ports, since those are usually undefended and easy pickings, allowing you to push back through their country and finally actually capture a port from the inside.

That’s everything you need to know about how to use Floating Harbor in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

Though most players tend to think only about land battles, naval warfare in Hearts of Iron 4 is also extremely important. Knowing how to control the seas is a huge part of the game, as you will otherwise never defeat countries like the United Kingdom or Japan.

However, there are many who have managed to win World War 2 many times and still have no idea how navies work. The main reason why nobody really knows how to use them is because they always get new updates that change how they operate.

Recommended Read: How to Increase World Tension in HOI4

Luckily, things seem to have settled down lately and the strategy to win using them is always the same, no matter what country you choose.

So, in this guide, we will talk about everything related to navies in Hearts of Iron 4: research, naval combat, ship types, how to set up a fleet, doctrines, and how to win every battle that your boats will participate in.

Table of Contents

• Naval Research
• How Does Naval Combat Work in HOI4?
• How to Set Up a Fleet
• Naval Doctrines
• How to Always Win Naval Battles

Naval Research

Naval

We can’t talk about the navies in HOI4 before exploring and explaining the Naval Research category. The first thing you will find when opening the research tree will be a lot of hulls.

Hulls are the base of a ship. They are the base that will be used to put guns, engines, and many other important parts on the ships that you will design.

So, what you unlock here is just a big piece of a larger puzzle that won’t work until you put all the necessary upgrades on it.

The main things that evolve with each technological upgrade for a hull are speed, reliability, and range. The only problem is that their production cost will increase.

The upgrades under the Destroyer hulls that follow them with each upgrade are called Depth Charges, and they help in dealing damage to Submarines.

These will usually be very useful additions to convoy escorts that need to defeat the raiding Submarines destroying your whole supply of Convoys.

Under the Cruiser hull tech, you will find a list of Armor upgrades. Generally, avoid researching these unless you really want to make your Battleships extremely sturdy.

Their speed debuff will usually cause problems for the ships and the rewards are just not worth the cost.

A vital upgrade will be the one under Submarines, which are available around 1940, which lowers the visibility of subs. This will be extremely important, so get them as soon as possible if you use subs often.

Naval Support

The Naval support research category exists purely to make your ships better and naval combat to go smoother for your side.

The Armaments sub-category is the guns that you can put on your ships. All of the hulls you researched beforehand are useless unless you get some good batteries to put on them.

Torpedoes are special upgrades that will allow your ships to deal critical damage to Battleships and Carriers.

The Fire Control tech is extremely valuable, and you should always research it when possible since it just gives a flat bonus to all attack stats for all the fleets in your navy.

Transports will also be vital if you plan on doing naval invasions. Even if you think you’re never going to do them, it’s still a better idea to get the tech than to reach the moment when you need to use them and don’t have the necessary research.

The Mine Warfare upgrades are decent. You’ll likely only need the main line ones that increase mine damage since you don’t really want to waste slots on putting minelaying upgrades on your ships.

How Does Naval Combat Work in HOI4?

In HOI4, naval combat isn’t as common as land battles.

The main reason is that you will have to plan for them accordingly for a long time, and a big confrontation between fleets will usually result in almost total destruction of one of the sides.

Otherwise, you will spend most of the time fighting to destroy Convoys or to protect troops doing a naval landing.

When two enemy fleets find each other, they will start engaging. There are 4 lines where the ships can take their positions:

• Screening Group
• Battleline
• Carrier Group
• Submarine Wolfpack

When battle starts, based on their speed and who spotted who, the ships will quickly move to get in position while the battle starts.

The ships will attack each other for a while until one side realizes that it will lose, so they will attempt to retreat.

During the retreat phase, the losing army will lose most of its navy as the pursuing navy will do its best to leave no ship standing.

Screens

The Screening Group, also commonly known as Screens, are made out of Destroyers and Light Cruisers, and their main role is to protect all of the heavy hitters from enemy fire.

Since they’re fast and resistant (with the right design), they go in the front and bear the full force of the enemy fleet.

They usually have enough speed to retreat when they take too much damage, which allows other screens to take their place in the frontlines.

They work very much like a shield for the whole navy since otherwise, the torpedoes used by the enemy fleet would tear through the heavy ships.

There is a stat that tells you exactly how well the screens are doing their job, called Screening Efficiency. The main reason why Screening Efficiency is very important is because it directly lowers the chance that torpedoes will hit your backlines.

A torpedo has a 100% chance of hitting when it fires, which is lowered by the Screening Efficiency. Each Battleline and Cruiser Group ship will need at least 3 screens.

This means that a fleet with 3 Heavy Cruisers and 1 Carrier will need 12 screens to be fully protected from the menace known as torpedoes.

Generally, they are the most important part of any fleet, and since they are easy and quick to produce, most players only concentrate on building them throughout the game. This is usually the strategy for any single-player game since the starting fleet for powerful countries is more than enough.

Usually, the Destroyers exist to take the damage while the Light Cruisers fight the enemy’s screen and try to take it down to get to the weaker backline.

Screens usually use Light Guns, which deal damage to the first non-occupied line in front of them.

Battleline

The Battleline is directly behind the Screening Group and their main role is to deal damage. They aren’t generally made to withstand attacks, and they are very vulnerable to torpedoes, which is why the Screens are so important.

Part of the Battleline are the Battleships and the Heavy Cruisers. Their main role is to deal the most amount of damage to both the Screens and the enemy Battleline, as they can get the largest amount of guns on top of them.

Battleline ships usually use Heavy Guns, which deal damage to the first two non-occupied lines in front of them. This normally means either the Screens and the Battleline or the Battleline and the Carriers.

Carriers

The Carrier Group is the furthest away from the battle, with ships such as the Carriers and Convoys. The purpose of this line is to attack the ships without actually getting hit by the opposing navy.

Since Carriers usually hold a lot of planes, their purpose is to survive while the bombers on top of them deal heavy damage to all the ships that are taking part in the battle.

Because they’re the furthest from the battle, they are protected by both the Screens and the Battleline when it comes to torpedoes, which would deal incredible damage if they managed to get through.

Submarines

The Subs have their own special line, which is under all of the others, that can be attacked using Depth Charges if you first manage to find them.

How to Set Up a Fleet

There is only one correct way to set up your fleet in HOI4, and that is to stack all of your ships into one single, huge task force.

Though the “smarter” way would be to make special fleets that each have its mission, you would generally be a lot better off by just putting all of your ships in a single giant fleet.

Since one battle in HOI4 will instantly decide if you’ve lost all your fleet or not, it’s better to make sure you can always win these kinds of fights.

Otherwise, you will likely get destroyed as a random fleet finds your smaller ones and instantly comes in full force to destroy you.

The only other fleets you might want to set up are convoy raider submarines since they are incredibly annoying and can destroy countries, and minelaying destroyers/subs, just to get an advantage in certain regions where you know you will have to fight at some point.

Otherwise, use a single ship to patrol the waters where you want total supremacy and set all of the deathstack fleet on the Strike Force command. This means that they will instantly join in the fight when someone finds enemy ships in the naval region.

Also, a very important piece of advice, never delete ships! Even if they’re the worst ships in the world, they will be very useful in the huge battle you will have with your main enemy.

Since the main goal of a navy is to win one single game-deciding battle, every ship will count.

In the worst case, you can just refit them to fit your needs better and find a use even for the early hulls pre-WW2.

Naval Doctrines

There are three naval doctrines that you can choose from:

• Fleet in Being
• Trade Interdiction
• Base Strike

The Fleet in Being doctrine focuses on making your ships better in battles. This means that they will get the necessary bonuses to excel in the occasional naval fights that happen in HOI4.

If you don’t have a reason to do something different, always choose this doctrine!

The Trade Interdiction doctrine is useful for harassing enemy countries’ Convoys. If you want to stop their supply of resources and likely ruin their land armies, Trade Interdiction is a really good choice.

However, this should only be chosen if you are a minor country without a real navy.

Never choose Base Strike. It helps you improve Carriers, which aren’t really the ships that win you battles. Just avoid this doctrine at all costs. It’s the equivalent to Mass Assault for ships.

How to Always Win Naval Battles

So, first of all, set up a huge fleet with all of your ships. There’s no other way to do this. Then, make sure to invest in the Fleet in Being doctrine. As specified earlier, this is the only one that will help you win wars.

If you started as a country with a great navy from the start (UK, US, France, Italy, or Japan) then you will only have to produce Destroyers and maybe Light Cruisers the whole game.

This way, you can make sure your huge fleet always has 100% Screen Efficiency and that it is protected in all battles.

Then, set up your fleet in three important naval regions on Strike Force. This will increase your intel in the region and give you naval supremacy, protecting you from any kind of annoying naval invasions.

Once you feel like you have enough intel in the region, you can send one or two destroyers to patrol in the region, trying to find enemy fleets.

This will usually result in them finding someone, moment when your huge fleet will come to destroy anything standing in their way.

Generally, it is best to avoid naval battles since you never know what can happen. The major powers all have huge navies with similar capabilities, and there is no way to predict how the battle will go. It’s basically a 50/50 toss.

Your main goal will always be capitulation, so try to launch naval invasions or just protect yourself from them.

You don’t even need to engage to do this, as the Strike Force command will assure naval supremacy while also generally avoiding battles.

That’s everything you need to know about how navies work in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.