Air warfare

From Hearts of Iron 4 Wiki
Revision as of 03:33, 25 June 2016 by Potski (talk | contribs) (Detection: Added more information, and clarified areas that were uncertain in original text)
Jump to navigation Jump to search

[Multiple locations]

Air warfare consists of the deployment of air wings to Strategic Regions, where they can undertake missions targeting Production, Construction, Infrastructure and other Units. Given that Air warfare is the only type that directly affects all 3 types of combat (on top of the strategic targeting), the air war is something the player must take into account when devising successful battle plans.

Note: There is not yet a way to explicitly assign Air Wings to battle plans.



Each air base can support up to 200 aircraft per base level and the maximum air base level is 10, for a maximum of 2,000 aircraft. Small aircraft (fighters, close air support and naval bombers) of the carrier model may also be based on aircraft carriers.


Each Air Wing can be assigned to a single Strategic Region, where it can perform the possible missions for its type. With the wing selected at its air base, right clicking on an air region in range assigns it to conduct missions in that region. Then left clicking shows assigned wings and conditions in that region. Each wing present may be given an available mission. Pressing F3 will display the Air Region Map Mode. If your country (or faction) has air superiority in a region, it will be tinted green. Conversely, if the enemy has air superiority in a region it will be tinted red.

Type Missions
Fighter Air Superiority, Interception
Heavy Fighter Air Superiority, Interception
Naval Bomber Naval Strike, Port Strike
Tactical Bomber Close Air Support, Strategic Bombing, Port Strike
Strategic Bomber Strategic Bombing
Close Air Support Close Air Support, Naval Strike, Port Strike
Transport None
  • Close Air Support: Attacks enemy land units directly.
  • Air Superiority: Prioritizes attacking enemy fighters. Gives a bonus to land units in the area.
  • Kamikaze Strike: Special mission unlocked with a Japanese national focus. Prioritizes inflicting maximum damage against sea targets, at the cost of aircraft.
  • Interception: Prioritizes attacking enemy bombers.
  • Naval Strike: Attacks enemy ships at sea.
  • Port Strike: Attacks enemy ships in port.
  • Strategic Bombing: Attacks enemy constructions.

Transport planes have no missions. They are required to execute paradrop plans. Unlike in HOI3, they are not used to drop supplies.

Assigning more than one mission to an air wing will not result in simultaneous execution of all these missions. For example, if the Close Air Support and Strategic Bombing missions are activated for Tactical Bombers, they will usually perform the Strategic Bombing first, until there are no more active constructions in the area.


Air wings are a group of air units attached to an air base. Air wings can be assigned to an air region called "area" inside Hearts of Iron IV. Once assigned to an air region, one or multiple missions can be activated for each wing assigned this area (see advice in previous paragraph). Air wing size can take any value between 1 and 1,000 aircraft.

If their air base is over-run by enemy divisions by taking control over the state the air base is in, then the air wings will automatically redeploy to another air base under friendly control.

Air combat (fighters)

This section exclusively develops on the topic of air combat, aircraft versus aircraft. Using information available in the defines.lua file, it's possible to speculate that air combat simulation approximately follows these steps:

  • Detection: If enemy airplanes are not detected in the region, interceptors (defending fighters on interception mission) will not take off.
  • Target acquisition: This phase will determine what's the maximum possible damage that air wings can do and also which type of aircraft will receive the damage depending if it's an air superiority or intercept mission.
  • Combat simulation: This phase will determine how much damage is done or received in each round of combat.
  • Rest: The air wing rests for 3 hours after combat, then it can be sent in mission again.


The following variables, or defines, are known in order to resolve the detection phase:

  • Base detection chance from aircraft: 5%. This value can be increased through doctrines that provide Interception detection or Fighter detection.
  • Detection chance from effective aircraft: 2,000 planes are required in the air region for the base detection chance to apply, interpolated otherwise.
  • Detection chance without search mission: -50%. Planes which don't have a search mission (such as bombers), only count at 50% towards the effective aircraft total.

Example: if you have 200 fighters on air superiority these will count 200 towards the effective aircraft total. If you have 100 CAS on port strike, they will only count 50 towards the total. This will give an overall amount of 250 effective aircraft. If your doctrines have not increased the base detection chance (5%), this will produce a detection chance from the 250 effective planes in the region of 0.625%

  • Detection chance from radars: 25%. Radar stations have a range of 20 to 220 pixels (140km to 1565km) from the center of the State they are built in. The range is interpolated based on the radar station level (1-6). The area covered by the radar station will be shown on the map in air mode, coloured a darker blue than normal. The bonus is interpolated from the percentage of the provinces in the air region which are covered by radar. You can use a single radar station in a state with a central position (most regions can be completely covered by a level 2 or 3 radar), or radar stations in more than one state. If the areas covered by multiple radar stations overlap the affected provinces will stack, but the total bonus will never go above 25%. Radar stations in an another region can also count, if their range covers part of your region. So radar stations on land can cover the naval zones in a nearby naval region.
  • Detection chance during the night: -20%. This value means that interceptors can't detect aircraft at night without a number of air doctrines and/or good radar coverage.
  • Detection chance from occupied provinces: 10%. This bonus is 10% for occupying the whole state. If the occupation is split between two or more countries, then the 10% bonus is divided depending on the number of provinces each of them occupies out of the total in the state. So if you occupy 150 provinces in a state with 200 provinces you will get 7.5% detection chance. If your enemy occupies the other 50 provinces they will get 2.5% detection chance. This bonus applies to detection throughout the air region.

Once the detection chance is established, then it gets modified by efficiency modifiers which serve to determine how many aircraft are detected.

  • Base detection efficiency: 10%. Once something is detected, the base detection efficiency says that 10% of all enemy aircraft are "found" or located.
  • Radar detection efficiency: 70%. Radar coverage will allow an extra 70% of all enemy aircraft to be "found" or located.
  • Random factor: 10%. The defines add a 10% random factor to detection efficiency. It's not clear if the factor can have a negative value or if it's binary (0% or 10%).

Target acquisition

Once aircraft are detected and the number of detected aircraft is determined, it's necessary to find out who will receive the damage resulting from the combat simulation. In the case of an air superiority fight, the answer is straightforward: the enemy fighters.

  • Base number of attack passes: 10%. This value multiplied by the attack value of an air wing will give the base number of passes each aircraft can do in single combat. An "attack pass" gives a chance to do damage against an aircraft. Note that, just like army divisions, an air wing with different models of aircraft will average out their value for the entire air wing so that any one fighter will be indistinguishable from any other fighter in the air wing. But the combat simulation is done at the single aircraft level.

In the case of interceptors, they possibly have multiple kinds of targets: escort fighters or the bombers themselves. The interceptors want to intercept or shoot down enemy bombers as much as possible and a few variables will increase or decrease their chances to roll attack damage on the bombers instead of escort fighters.

  • Base chance to attack bombers directly: 25%. Interceptors have a base 25% chance of "bypassing" the escort fighters and to attempt to inflict damage directly to bombers. (in the defines, this is called the "Combat escort pass chance")
  • Multiplier to chance to attack bombers directly: 25%. When there's a combat statistics difference (for speed or agility) between the interceptors and the escort fighters, the chance to "bypass" the escort fighters is modified. 25% of the statistical difference is used to add or substract to the base chance to attack bombers directly.
  • Maximum chance to attack bombers directly: 95%. Regardless of how better the interceptors are, they will never have more than 95% chance to "bypass" the escort fighters.

Now, the number of aircraft in the simulation will almost never be the same. The numerical advantage on one side provides a chance to result in more 2vs1 single combat simulations, instead of the default 1vs1.

  • Gang chance from combat aircraft advantage: 40%. It appears this value applies on the difference in number of aircraft and the result gives the number of 2vs1 combat situations.
  • Combat stack limit: 2. This value determines how big a gang situation can occur: 2vs1. This also implies there's no advantage in having more than a 2:1 air superiority for air combat purposes.

Also of note, the defines have a modifier to the number of passes that can be done against bombers or against air superiority missions (in single, 1 versus 1, fight). At the time of writing this, the modifier is set to "1", meaning the number of passes is not affected, but this could change in the future.

Combat resolution

  • Chance for pass without event: 60%. For each "attack pass" that an aircraft does, there's a 60% chance it will result in an "uneventful pass", no damage done, but also no damage received.
  • Factor of the effect of higher speed on attack chance: +25%. This factor applies only in air superiority vs air superiority combat only. During those air combat, the speed avantage of the fastest fighter wing will give that wing a +25% chance to attack first.

For the 40% of passes that are not uneventful, there's still a chance the pass doesn't result in a successful hit for the attacker:

  • Base chance to hit for each pass: 60%. A hit means that the target aircraft receives 1 point of damage. The cumulative damage will need to reach the air defense value before the target is shot down.

Here's an average (incomplete) result for 1vs1 scenarios: each air wing has an attack value of 16. This means that each plane will do 1.6 attack passes in each round (on average) and 0.96 of these will be uneventful (on average). One of the two planes will attack first and 0.64 of its attack passes will give it a 60% chance to score a success (it's possible that the same define was entered twice in defines.lua, but with 2 differents strings). Out of those 0.64 eventful attack passes, 0.384 (on average) would result in a success and then the other fighter in combat would roll for it's attack value. Rinse and repeat until one of the fighters is shot down or the combat ends.

This base chance to hit for each pass is modified depending on different situations:

  • Maximum bonus to hit chance due to better stats: +20%. A plane with a "combat statistics advantage" can obtain up to 20% to its chance to hit for each pass it does.
  • Bonus to hit chance from 2vs1 situations: +18%. When a single combat simulation is done in a 2vs1 scenario, the "ganging" airplanes receive an 18% bonus to their chance to hit for each pass they do.
  • Maximum damage reduction from higher agility: +20%. Higher agility than the attacking aircraft will help the target reduce the damage it takes.

Also important to note, there is a maximum number of air wings allowed in a combat simulation: 6. With each air wing currently able to support up to 1,000 aircraft, this means there's a theoretical limit to the number of aircraft that can enter a combat simulation: 1,000. More importantly, a low number of aircraft in each air wing will not improve the situation in any way past 8 air wings. It's not clear at the moment if the limit of 8 air wings is for each side or the total for both sides.


Once an air wing has completed a combat mission, it needs to rest at the air base for 4 hours before it can be sent in combat again. It's as of yet unclear how long a combat simulation lasts or if the rest period applies to air wings that could not take part in the simulation due to the air wing limit.

Calculation of airplane stats difference

During the combat simulation, the difference in value of Agility and Speed statistics will impact a number of variable such as the chance to bypass escort fighters or the chance to hit an enemy fighter.

  • Speed difference multiplier: 25%. A speed difference between two aircraft will provide a "combat statistics advantage" equal to 25% of the speed difference.
  • Agility difference multiplier: 100%. An agility difference between two aircraft will provide a "combat statistics advantage" equal to 100% of the agility difference.

For example, without any variants, a 1940 fighter will have an advantage of 150km/h in speed and 15 points of agility over a 1936 fighter. This will result in a (150*0.25%)+(15*100%) = 52.5 combat statistics advantage for the 1940 fighter.

  • Maximum agility factor: 3. This is unclear, but it appears that for the purpose of damage reduction, the aircraft with the higher agility will not get any marginal statistical advantage if its agility is 3 times higher than the lower agility. This is effectively a cap on damage reduction.

Known unknowns

  • One define in particular mentions a modifier on who attacks first, but the base value or the value for each mission is unknown.
  • The air combat simulation seems to resolve combat on a 1vs1 level, or possibly a 2vs1 scenario, but it's unknown how many rounds of combat there are.
  • Some defines are no longer in use in the simulation, but it's impossible to know which. Therefore, any of the information above may be inaccurate.

Air superiority

Every 50 points of air superiority advantage in a strategic region gives a +1% air support bonus to land combat?


Air combat has a chance of generating aces. An air wing may be assigned up to one ace.

Ace Chance Fighter Effect Bomber Effect Support/Naval effect
"Good" 0.9 +3% Air Attack
+3% Speed
+5% Agility
+5% Bomb Targeting
+3% Range
+5% Naval Strike Targeting
+3% Bomb Targeting
+5% Agility
"Unique" 0.4 +6% Air Attack
+5% Speed
+10% Agility
+10% Bomb Targeting
+6% Range
+10% Naval Strike Targeting
+5% Bomb Targeting
+10% Agility
"Genius" 0.05 +10% Air Attack
+8% Speed
+15% Agility
+15% Bomb Targeting
+10% Range
+15% Naval Strike Targeting
+8% Bomb Targeting
+15% Agility

The effects are scaled inversely by the size of the wing relative to 100 planes, to a maximum of x10 at 10 planes.

Close Air Support

Whenever a battle takes place on the ground an airwing assigned to the CAS mission can join and do damage to the enemy troops. Mulitiple airwings on the CAS mission can join; however, one air wing cannot split up and join two or more battles. The number of planes from the airwing joining the battle is dependent on the enemy troop frontage. The number of planes able to join the land battle is 3 times the used enemy frontage.

The allowed CAS frontage is adjusted by the type of terrain in the province where the land battle takes place. The following factors applies:

  • Forest: -10%
  • Urban: -50%
  • Hills: -5%
  • Desert: -0%
  • Plains: -0%
  • Mountains: -10%
  • Marsh: -0%


  • One forest land battle takes place in the air region. The enemy frontage is 20 which allows 3x20*0.9 = 54 planes on the CAS mission to join the battle. CAS wings will join the battle to fill up to 54 planes.
  • Two land battles take place in the air region. The first battle is in a forest and the enemy frontage is 20 which allows 3x20*0.9 = 54 planes to join in. However, each of the two air wings is in stacks of 50 planes. If they both join the battle, the 2nd airwing wastes 46 planes that cannot join another battle.

In the defines.lua file COMBAT_MAX_WINGS_AT_GROUND_ATTACK is set at 30, which suggests that up to 30 CAS air wings can be active at the same time in an air region. It is unclear if this affects the maximum air wings limit of 6 for fighters.

How CAS damage is calculated is currently unknown.

CAS planes also have an air superiority stat, which indicates air superiority is not only for fighters. As long as an CAS wing is active it will contribute to the air superiority in the air region.


Air Mechanics/Combat/Mission "Quick" Guide