While part 1 of this tutorial guide looked at the economy as the foundation of your country’s power, parts 2, 3, and 4 will focus on the military: the primary application of your country’s power. {If you haven’t checked out part 1 of the tutorial, you can access it by following the link here.} Having the strongest economy in the world doesn’t mean much if you can’t leverage it with a competently designed, well-trained military. 

In this guide, we will look specifically at land combat. Land combat is by far the most prevalent form of combat in the game. As such, it will be the largest of the military guides. We will look at basic combat mechanics, combat width, logistics, an overview of unit stats, as well as terrain modifiers. 

Combat Mechanics 

Combat in HOI4 is a combination of unit statistics, modifiers, and dice rolls. Understanding how these all interact with one another is vital to finding success on the battlefield. 

Cardinal Stats: Organization & Strength

Organization is the single most important stat for your divisions. It represents the willingness and ability of your units to fight. If your division’s organization is at zero, it can’t fight. 

Organization is lost from movement, combat, and lack of supply. If your unit is in supply, it will recover over time. Your unit’s organization cap can be increased with various doctrines that can be found in the officer tab and unlocked with army experience. 

Strength represents, well, the strength of the division. It is always represented as a percentage of 100. Strength includes both a division’s manpower and, more importantly, its equipment. If your division is not at full strength, its stats will be lowered accordingly by whatever equipment it is missing. If divisions are in supply, they will reinforce automatically as long as there is equipment and manpower available. 

Offensive Stats: Soft Attack and Hard Attack

Soft attack measures how many attacks your unit can make against an enemy unarmored (soft) unit. In this case, the higher the number the better. Certain battalions like artillery provide a substantial amount of soft attack. 

Hard attack is the same mechanic but for attacks against armored (hard) units. These values tend to be much lower than soft attack for most battalions. Some battalions such as anti-tank, however, provide a large amount of hard attack.

Defensive Stats: Hardness, Breakthrough, and Defense 

Hardness is the ratio of enemy soft and hard attacks that your division will be affected by. It is always expressed as a percentage of 100. Essentially, hardness is supposed to represent the percentage of the unit that is armored.

If a unit has a hardness of 10%, it means that it suffers 90% of enemy soft attacks and 10% of enemy hard attacks. Conversely, a unit that had 90% hardness would only suffer 10% of enemy soft attacks while taking 90% of their hard attacks. 

Because of how much more soft attack units tend to have compared to hard attack, it is always worthwhile to make your units as hard as possible. 

Defense is a measure of how good your unit is when holding ground. If your unit’s defense stat is higher than the enemy’s attack stat (soft and hard together in the correct proportion), then your unit only has a 10% chance of taking a ‘hit’. If the enemy has higher attack than your defense, that chance goes up to 40%. 

Breakthrough functions the same as defense except that it applies when your unit is attacking. Thus, having high breakthrough is crucial for your attacking units. 

Each ‘hit’ in combat deals 1d2 damage to your unit’s strength and 1d4 damage to your unit’s organization. As stated earlier, when a division’s organization hits zero it must disengage from combat and retreat. 

Because of its high breakthrough, the German motorized division is able to ‘absorb’ all of the attacks from the Polish division only getting hit 10% of the time
Because of its high breakthrough, the German motorized division is able to ‘absorb’ all of the attacks from the Polish division only getting hit 10% of the time

Combat Width 

Combat width is very important to understand in HOI4. Not building divisions intelligently in regards to width is probably the number one mistake new players make when first playing the game. Having trouble pushing through the Low Countries on your way to Paris as Germany? Combat width probably has something to do with it. 

Divisions in HOI4 take up a certain amount of space at the front. This is referred to as combat width. Ideally, you want to completely fill up all available width but not exceed it. If you exceed the available combat width, all of your units involved will suffer stacking penalties.

Since the No Step Back DLC and update, each different terrain type now has a different combat width. There is no longer a ‘one-size fits all’ width template for divisions. 

All tiles have a base combat width. Any additional attacks coming from different tiles will increase the width of the battle by half or a third of the original base width. For example, plains and deserts both have a base combat width of 90 with an additional 45 added for attacks incoming from a different tile. So, if a plains tile was being attacked from three different tiles, the combat width would be 180. But, if a mountain tile (width 75) was being attacked from three different tiles, the combat width would only be 125. 

Here is a list of all-terrain types and their combat widths.

Plains – 90 (45), Desert – 90 (45), Forest – 84 (42), Jungle – 84 (42), Hills – 80 (40), Mountain – 75 (25), Marsh – 78 (26), Urban – 96 (32)

With these widths in mind, a common division template players build is a ‘9-1.’ This is 9 battalions of infantry and 1 battalion of artillery. It has a width of 21. 21 is a nice width because it allows four divisions to attack most terrain types without any stacking penalties. 

We will dive further into terrain and how it affects combat later in this guide.

Combat width is 90 in plains provinces. If I attack with a division to the North, it will expand the width to 135


“Amateurs study tactics, professionals study logistics.” A common military saying that also strikes true for HOI4. Without supply, even the most experienced, well-equipped division will be useless. Divisions out of supply will suffer a progressively harsher penalty depending on how much supply they are short. If a unit is completely out of supply, it will not recover organization and will slowly lose it.

Since the No Step Back DLC, logistics has gotten a rework. While being difficult to understand at first, once you get the hang of it, it is actually very straightforward.  

Supply Draw

Each of your divisions has a supply use stat. This information can be found on their division template. Supply use is how much supply is needed to keep the division in supply and performing at full capacity. Keeping supply use as low as possible is recommended and the logistics support company does just that. More on that later. Note that unlike previous versions of the game, supplies no longer need to be produced. 

Railways and Throughput

The main mover of supply is now constructible railways and trains. Level 1 railways provide 15 supply to the hub they are connected to. Each additional level of railway provides another 5 supply to the hub for a maximum of 35 with a level 5 railway. In order to get the desired throughput, all railways from the capital to the supply hub must have the appropriate level of railway. Throughput is always based off the level of the lowest relevant railway for the connection so be on the look out for bottlenecks!

Here you can see a bottleneck in supply due to the railway level being too low. By clicking the upgrade bottlenecks button, all of the relevant railways all the way to the capital will be automatically queued up for construction

Supply Hubs

Supply hubs have a maximum range from which they can supply units. The ability for a hub to supply a unit gets progressively worse the further away a unit is from the hub. Eventually, a unit will be too far away and will be unable to be supplied from the hub. This is why when you are conducting offensives, it is vital to locate enemy supply hubs and capture them as without them, your offensive will quickly grind to a halt.  

You can increase the range of your supply hubs a few ways. The first is simply to increase the amount of supply that is getting to the hub. Having level 5 railway connections all the way to the capital really helps. 

You can also increase the motorization level of the hub. You can do this by clicking on the hub and then clicking on the horse icon and changing it the truck icon. There are two levels of motorization. Level 1 takes 40 trucks per hub and level 2 takes 80. Remember that these trucks do not require fuel but will suffer from attrition and enemy air attacks. 

Finally, you can increase the infrastructure level. Each level of infrastructure will allow the hub to transfer more supply to the next province over. Although it is a small amount, it is per each province so it adds up quickly. 

The dark red hashed lines show which provinces are currently in range of the supply hub. By clicking on the motorization button, the range will be increased to the brighter pink hashed lines

State Supply

Supply also comes directly from the states you control. The amount is based off the population level, the amount of Victory Points (if any) present, and the level of infrastructure. Keep in mind that this amount of supply is generally very low and to support any large amount of units will require a logistics network as we have previously discussed. 


“The two rules of warfare:

  1. never start a land war in Asia.
  2. never march on Moscow in the winter.

Another military maxim that also strikes true for HOI4. Since No Step Back, weather and weather effects now greatly affect your logistics and thus your ability to conduct effective military operations. 

Both acute weather effects such as blizzards, sandstorms, and storms as well as seasonal climatic effects like cold or hot temperatures, deep snow, and mud can absolutely devastate a logistics network. 

Fighting in such conditions is ill-advised unless it is absolutely necessary. 

In the lower left part of the screen you can see the negative effect the snow has on logistics. Keep in mind this is only snow in December. It gets worse!

Air Supply

Finally, we come to air supply. If you are playing as a major nation, you may well have a decent-sized fleet of transport planes. It is possible to set them on the mission ‘air supply’ and have them drop supplies to your units. Keep in mind that if the enemy has air superiority, this will not go well. Additionally, the amount of supply that can be air dropped is relatively small so don’t expect to supply entire armies with it. It is more of a band-aid type of solution.

Unit Statistics

While we already looked at some key unit statistics like hard and soft attack, defense, etc, here we will go over some other stats. I won’t cover all unit stats but rather highlight some of the more important ones and explain how they function in the game. 

Armor and Piercing

If a unit has a higher armor rating than an enemy has piercing then it gets a massive boost in combat. It only suffers 50% of all enemy attacks hard or soft. Additionally, it deals an extra 50% organization damage to the enemy unit. If the enemy has more piercing than you have armor, then your units are ‘pierced’ and combat happens as it normally would without any bonuses or penalties. Piercing in HOI4 is all or nothing. It doesn’t scale. 

To add armor to your divisions add more hard units like tanks and half-tracks and remove soft units like infantry. You can also upgrade the armor level of your tanks. To improve your division’s piercing stat consider adding anti-tank battalions, anti-air, or tanks and tank destroyers. 

Keep in mind that armor and piercing are averaged for the entire division. If you have just 1 battalion of heavy armor or 1 battalion of heavy tank destroyers mixed with many battalions of infantry, the armor and piercing stats for the entire division will be reduced. 


HP in a division affects how much manpower and equipment you lose when your unit inevitably takes losses. Low-HP divisions will take more manpower and equipment losses for each % of strength lost. Infantry has the highest HP stat of all the battalions and is usually a core component of any division. This is why pure tank divisions fare poorly in HOI4. 

Air Attack

Divisions with a high air attack stat have the chance to deal considerable damage to enemy planes that are bombing them. Unless you anticipate having air supremacy, having some air attack in your divisions is usually a good idea. In addition, shooting down planes, it reduces the bonus from air superiority that an enemy might get. Finally, it also has the effect of increasing the division’s piercing stat by a fair amount. Your units can only engage enemy planes that are actively targeting them with ground attack. It has no effect on strategic and logistical bombing done by the enemy. 

Here we can see how having AA in my divisions is reducing my penalty for the Poles having air superiority


Manpower is how many men are required to keep the division at full strength. If you are a nation pressed for manpower you can either increase the level of conscription law (although this has heavier penalties for your economy the further you go), or design divisions that are less manpower intensive. Infantry is a very manpower-intensive battalion whereas artillery or armor provides much more firepower for less manpower cost. 


Entrenchment is how much of a bonus your units will get from digging in. Any unit that is stationary and not in combat will start digging in. Dug-in units receive combat bonuses for their offensive and defensive stats. This only applies when they are attacked however as it is lost as soon as they move. 

The higher a unit’s entrenchment stat is, the higher its dug-in bonus will be. Most units share their country’s base entrenchment stat but it can be increased by adding an engineer support battalion as well as certain command traits and doctrines. 

Trickle Back and Exp Loss

If you add the hospital support company, you will see trickle back and exp loss added to your unit’s stats. Trickle back works by adding a small amount of manpower back to your national pool from any combat losses you might take. Exp loss means that each casualty your division takes will bring down the overall unit’s experience level by a lesser amount. 

While these bonuses sound amazing and great to have, unfortunately, they are not. The way HOI4 is set up, the hospital support company is very expensive in terms of industry and opportunity costs. Additionally, most nations never have manpower shortages so it’s only worth it in a few niche cases. 

Terrain Modifiers

We already looked at the terrain as far as it pertains to combat width. Now let’s examine how terrain impacts combat as a whole. 


Plains are the basic terrain type in HOI4. They have no modifiers whatsoever. This makes them the easiest to attack but the hardest to defend. 


Found in North Africa and the Middle East, deserts are common enough in HOI4. They don’t give any combat penalties but they are taxing logistically. Fewer supply moves from hubs and supply trucks take more attrition. Additionally, all equipment is subject to a +15% attrition penalty. Units also suffer a -5% to movement cost. Finally, your generals have an increased chance to fall ill. In deserts, less is more. Try to make due with fewer units. Large armies have no place here. 


Forests give a -15% attack penalty as well as -50% to movement cost. There is also a small penalty to supply flow from hubs and truck attrition but it isn’t as bad as in other terrain types. Having air superiority will only provide 90% of its bonuses here. While attacking into a forest isn’t ideal, it also isn’t horrible. 


Fortunately, jungles are not found in the main battle arena that is Europe and its periphery. However, the Asian, African, and South American theaters have plenty of them. Jungles give some nasty penalties. -30% attack, -50% movement cost, +20% attrition rate, as well as a very large truck attrition rate means that they are not fun to attack or defend. As with deserts, your generals have an increased chance of falling ill here. Air superiority counts for significantly less here so it is a terrain that can act as an equalizer for two mismatched opponents. 


While definitely an idyllic landscape, hills aren’t great to attack into. They give a -25% to attack and -50% to movement cost. Air superiority is only 95% effective here and there is a small penalty to supply flow from hubs and truck attrition. If you anticipate fighting a lot in hills, it would be worthwhile to recruit mountaineers who will have bonuses in such terrain. 

Due to their special training, Mountaineers actually receive a terrain bonus in hills


Mountains are big hills. They give a whopping -50% to attack and -100% to movement cost. Supply flow from hubs is reduced and truck attrition are significant here as well as a general +30% attrition rate on all equipment. Mountaineers have milder versions of the attack and movement penalties so if combat in mountains can’t be avoided, it is best to use them. 

These harsh penalties along with a narrow base width of 75 means that mountains are one of the most difficult tiles to attack.


Just like the Dead Marshes in the Lord of the Rings lore, marshes in HOI4 should be avoided at all costs. This is the absolute worst terrain to fight in. +100% movement cost, +35% attrition rate, -40% attack, increased chance of illness, and massive supply hub flow and truck attrition penalties make this terrain type a nightmare to deal with. Forcing your opponent’s divisions into marshes while avoiding them yourself is a sound strategy. 


Urban areas are very common in Europe with most countries at least having a few tiles. Urban areas give a +20% movement cost, and -30% attack penalty. Air superiority is only 50% effective here. Urban is the only terrain type that actually provides a supply hub flow bonus. As previously stated, urban areas have the highest combat frontage at 96 which means that being outnumbered here will hurt the most. However, if they can match enemy numbers and dig in, defenders can be very difficult to evict from urban tiles. 

Pulled from the Hoi4 wiki, here is a terrain map showing where all the different terrain types are in the game

Where Water Meets Land

Although not actually being tiles, rivers and straits need to be discussed here as well. In HOI4, all rivers are classified as either small or large. Small rivers give -30% to attack and -25% to movement cost. Large rivers give -60% to attack and -50% to movement cost.

Amphibious assaults across straits or across open water with transport ships gives a large -70% to attack. Some of these penalties can be lessened through general traits and special abilities. Like mountaineers in their niche terrains, marines perform well here. 

Keep in mind that all of these terrain bonuses and penalties are just the base. Every battalion has its own terrain penalties or bonuses that stack with these. For example, a heavy tank battalion will perform much worse than an infantry battalion when attacking a forest, etc. 

By now, you have the basics of land combat in Hearts of Iron 4. It is a lot of information to digest. But over time, it will become second nature to you. In the next section of the guide, we will look at combat at sea and in the air.

See you there!

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