Air warfare

From Hearts of Iron 4 Wiki
Revision as of 21:16, 15 August 2019 by Bitmode (talk | contribs) (Superiority: Condense table so it's easier to see the two exceptions)
Jump to navigation Jump to search

Air warfare consists of the deployment of air wings to Strategic Regions, where they can undertake missions targeting enemy air forces, land units, naval units or buildings. Given that Air warfare is the only type that directly affects all three types of combat (on top of the strategic targeting), the air war is something the player must take into account when devising successful strategies.


The map mode icons.

Air warfare is managed in the corresponding Strategic Air map mode. This map mode can be activated by either:

  • clicking on the airplane button located in the lower right corner of the main screen
  • pressing the F3 hotkey
  • clicking on any air base icon on the map (this will also open the air base view)

Most air operations work on the scale of strategic regions (called "area" in some info screens), which usually comprise a number of states or a naval zone. These regions are shown by name in the Strategic Air map mode.

Air Bases

An air base icon on the map in Kanto state in Japan, and carrier fleet based at the naval base in the same state

Air base Air bases are needed for the operation of aircraft. They are state-wide buildings, which may be constructed or repaired at the Construction screen. In contrast to other state-wide buildings, air bases are located in a specific province (which is fixed per state) and control of this province determines who can use the air base. When an air base gets captured, planes automatically relocate to other air bases if available and won't be lost.


The air base view of Kanto state showing a capacity of 1200 (level 6) and 253 aircraft stationed there

Each land-based air base can support 200 planes per base level without any penalties. The maximum air base level is 10, for a maximum of 2,000 aircraft. All types of planes may be located at these air bases, including carrier-capable models.

The capacity of an air base is shared between allies. The tooltip for the air base shows the total number of planes located there (and a list of the countries with air wings and the types of planes). If the total number of stationed planes exceeds the capacity, every additional percent of planes causes a 2% overcrowding penalty. At 50% over capacity, the penalty reaches 100%, so it is very important to manage the available capacity.

Air bases can be damaged by strategic bombing missions Strategic Bombing Mission.png. Damage will reduce the capacity the base can hold until repaired.

Carrier Fleets

The carrier fleet view is the same as the view of an air base on land, except that it lists each air wing under the name of the carrier(s) in the fleet. In this case, the two air wings are located on the carrier Ryujo in the fleet called 1 Koku Sentai. The wings are in standby, because the fleet is at anchor in the naval base.

Aircraft carriers act as additional, floating air bases. Their capacity is determined by the deck size stat of the ship and they only support carrier-capable aircraft.

Normally aircraft on carriers only participate in naval battles, but carrier task forces on hold outside of ports can launch missions in a strategic area. This may be very useful to provide some air support for an amphibious invasion when other bases are out of range.


The Air Forces screen show a list of all air wings. It can be opened from the Air Overview button Air Forces.png in the top right of the screen.

Air wings are a group of planes forming an air unit attached to an air base. A new air wing is deployed from the air base screen. An air wing may be created only if there are sufficient planes and service manpower available.

One air wing needs to contain at least 1 and at most 1,000 planes. They must all be the same type of plane; it is not possible to mix fighters with close air support, for example. It is possible to change the size of an air wing once it is deployed by clicking on an air base, then clicking on the top number on the left-hand side of each wing's row. The reinforcement level of an air wing represents the amount of planes an air wing has at full strength, and if the current number of planes is lower than the reinforcement level, new planes will be added to it as long as there are sufficient stockpiled planes of that type. If there are none, then reinforcement will take place when new planes of the correct equipment type are produced by military production lines.

Wings can be Split.png split or multiple wings of the same type Merge.png merged into one in the air base view. There is also a Reorganize option Reorganize.png that allows greater control over moving planes between two or more wings of the same type.

Coast of Japan air region with an air wing with 72 fighters assigned to it. The air wing is carrying out an interception mission Interception Mission.png .

Once a new air wing is created, it will take several days for the planes to arrive at the airport. The wing may be assigned to an air region and given missions immediately, but it will not carry out the missions until the planes arrive.

If an air wing is disbanded, then all of the planes will return to the equipment stockpile and will be available for deployment to other air wings.


Missions control the behavior of the wing in the assigned region. Note that while the selectable missions depend on the wing's type, they don't depend on the region. Most missions only make sense when operating over land or sea respectively.

Mission efficiency

The fighter wing from Kanto is assigned to the Home Islands region. Kanto is within that region (0 km range from the base). The range for the planes is 570km, which is sufficient only to cover 60% of the region, so there is a -40% penalty to Mission Efficiency. The tactical bombers have a range of 1000km which can cover the whole region, and they get no penalty.
The nearest Japan air base to China is Liaotung, which is 747km from the North China region. The CAS wing there only has a 700km range and suffers a -70% efficiency penalty, because the CAS can only cover 30% of the region. Japan owns two states within the region, including East Hebei. Building a new air base there before Marco Polo means the CAS can cover 84% of North China region, and receive only a 16% penalty.

The mission efficiency of a wing influences what percentage of its planes can actually carry out the assigned missions.

  • If the wing's range does not cover the entire strategic region, it will get a range penalty proportional to the provinces that are not covered.
  • Airbase overcrowding can cause a large penalty, as described above.
  • Bad weather conditions reduce mission efficiency
  • Wings newly assigned to a strategic region get a temporary, decaying penalty to mission efficiency. Therefore frequent region changes should be avoided, especially for bombers.

Deploying more planes can offset reduced mission efficiency to an extent, but basing planes closer to the center of the strategic region or using planes with longer range may be more efficient.

If the player does not control any bases within a region that they are attacking, then they are at a considerable disadvantage to their enemies, who do have control. The player might:

  • Choose tactical bombers to carry out close air support missions, instead of CAS, and use heavy fighters because of their longer range.
  • Try to capture an enemy air base as quickly as possible, so that the player can redeploy some fighters and CAS there. It might even be worthwhile if the player captures a state without an air base to build their own level 1 base there as quickly as possible. That will allow them to redeploy wings with up to 200 planes to be located within the region.
  • Use strategic bombers to bomb enemy buildings, including air bases. This might cause enough damage to their air bases to "even the odds" by reducing enemy Mission Efficiency. But this may only work if their air bases are already close to full capacity.
  • Using carrier fleets might also be very useful if the region has a coast where the player can (safely) anchor the fleet. Especially if the attack on the region is being carried out by a naval invasion. The carrier fleet can carry out the multiple roles of protecting the transport convoys, and providing shore bombardment.
  • Abandon trying to compete for Air Superiority with the player's fighters, and rely only on interception missions. Fighters on interception missions only take off and attack bomber wings if they detect a target. This causes lower losses of the player's fighters. It will give the player's enemy the Air Superiority bonus in combat however.

The Air missions ordered will be conducted regardless of weather, but bad weather reduces detection and efficiency and increases the risk of an accident at take-off and landing. The effects increase with weather severity, with sandstorms and blizzards being particularly bad. It may be advisable to put air wings on standby during such conditions.

Air superiority/Escort mission

Available for: Fighter, Heavy Fighter, Jet Fighter

Wings with this mission Air Superiority Mission.png will fight and disrupt any enemy air wings operating in the area. The air superiority mission doubles as escort mission, protecting bombers operating in the region by reducing disruption from enemy fighters. Air superiority mission efficiency bonuses increase the attack, defense and agility of the wing.

Close Air Support mission

Available for: CAS, Tactical Bomber, Jet Tactical Bomber

Close air support, also known as ground support, is the use of aircraft to assist troops in land combat. This is accomplished by putting Close Air Support (CAS) planes or Tactical (TAC) bombers on Close Air Support missions Close Air Support Mission.png that strafe and bomb enemy troops resulting in enemy manpower loss, enemy equipment loss, and chaos (reduction in enemy unit organization).

Wings with this mission will participate in land combat throughout the strategic region. This gives an attack bonus to friendly troops and directly damages organization and strength of enemy divisions. Divisional anti-air (AA) weapons reduce damage to the division caused by close air support attacks in proportion to the AA's ability to shoot down planes. Air support mission efficiency bonuses increase the attack, defense and agility of the wing.

The CAS air wing can split up and divide CAS planes to several land battles. It is therefore not necessary to use multiple CAS air wings. The number of planes from the air wing joining the battle is limited by 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 apply:

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

Example: One forest land battle takes place in the air region. The enemy frontage, from the landbased divisions, is 20 which allows 3x20*(1-0.1) = 54 planes on the CAS mission to join the battle. CAS wings will join the battle to fill up to 54 planes.

Interception mission

Available for: Fighter, Heavy Fighter, Jet Fighter, Rocket Interceptor

Wings with this mission Interception Mission.png will only participate in combat if enemy bombers or transport planes are detected. Interception mission efficiency bonuses increase the attack, defense and agility of the wing.

Strategic Bombing mission

Available for: Strategic Bomber, Jet Strategic Bomber, Tactical Bomber, Jet Tactical Bomber

Strategic bombing is the act of damaging enemy buildings, industry, and infrastructure via planes designed to drop bombs. Wings with this Strategic Bombing Mission.png mission can prioritize the type of target (such as airbases, radar installations, forts, infrastructure, etc.) within the strategic region by clicking on the proper button. Note that your bombers may get targeted by state-level "static" anti-air Anti-air (building).png (AA). Strategic bombing damage is about 120 damage per attack cycle for ~0.3 buildings destroyed. This damage appears to be distributed among all the targeted buildings (forts, industry, etc.) in the air region without regard to the number of air wings present. World War II bombers were notoriously inaccurate, and therefore the amount of bomb damage varies greatly from day to day.

Players carrying out strategic bombing should note:

  • Strategic bombers are very expensive to construct and in many cases a significant number are required to have any meaningful impact. Carefully consider the opportunity cost of committing many factories to a strategic bombing campaign.
  • If the enemy air region is heavily defended with fighters, the bombers may need to be escorted. Only heavy fighters have enough range to escort strategic bombers deep into enemy territory, but they can be beaten by light fighters.

Players subject to strategic bombing can respond in several ways:

  • State-level "static" AA Anti-air (building).png emplacements (built in the Construction interface or States view) will not only destroy the enemy's bombers, but they will also receive some of the bombs (diverting them from the factories, refineries, resources, and naval facilities that the defender needs to protect).
  • Strategic bombers can be fought in the air by fighters. Heavy fighters are more effective than light fighters in this role. Bombers are much slower and less agile than fighters, so players designing defensive fighters will find guns are most effective. Heavy fighters' larger range also means that they can be used to defend a larger area.
  • The Construction Repair Continuous focus will speed up the repair of damaged buildings. This will help the region to recover.

Players can assess the impact of their bombing and their defenses in the region's air combat screen (number of buildings bombed, percentage of bombers disrupted). The details pane of that window provides numbers across a long time frame.

Naval Strike mission

Available for: Naval Bomber, CAS, Tactical Bomber, Jet Tactical Bomber

Wings with this mission Naval Strike Mission.png target enemy ships, both inside and outside of naval battles. They may get targeted by naval anti-air. Air wings have a base 4% chance to detect or find an enemy fleet. This detection percentage is modified by other variables. To make detections more frequent at the expense of potentially reducing bombing effectiveness, make more smaller air wings.

Once an enemy fleet is discovered, a randomly assigned ratio of planes to fleet frontage is determined. Fleet frontage is calculated from the total hit points (HP or health) of the enemy fleet divided by 20. Typically, the ratio of attacking planes to fleet frontage is 1:1. Each plane assigned to the attack rolls to hit a target. If the plane hits, it does damage equal to the plane's naval attack (naval damage) value. In a fleet with multiple ships, the target is randomly selected (note: increased ship's surface visibility may increase its chance to be selected as a target...more visible targets are more often struck. This needs to be verified). For example, if a NAV1 hits a heavy cruiser 1, the NAV1 will do 1.5 points of damage. That is, the battleship will lose 1.5 hit points out of its total of 150 hit points.

Naval strikes using only airpower never attack enemy convoys carrying resources or supplies. They can attack enemy convoys carrying troops. However, convoys auto-repair between each attack, and most aircraft are too weak to sink a convoy in one attack. Only NAV2 and NAV3 have a sufficiently high naval attack value to sink troops convoys. The auto-repair mechanism also means that bigger wings are better.

The situation is quite different if naval strikes are combined with an attack by warships (including submarines). In this case, the resource and supply convoys can also be the target of an attack, and many different types of aircraft can be useful (i.e., not only NAV2 and NAV3).[1]

Kamikaze strike mission

Wings with this mission Kamikaze Strike Mission.png target enemy ships, both inside and outside of naval battles with increased damage to both sides. They may get targeted by naval anti-air.

Port strike mission

Available for: Naval Bomber, Tactical Bomber, Jet Tactical Bomber

A port strike mission Port Strike Mission.png is an air attack against enemy ships located in a naval base. Naval bases are located within provinces on land, therefore, port strikes can only take place in a region which covers land. The naval base itself will get damaged as well during successful attacks, but empty bases cannot get attacked.

At least 30% air superiority is required to perform port strikes (reference Defines NAir PORT_STRIKE_ENEMY_SUPERIORITY_LIMIT = 0.3). The number of airplanes involved in a port strike is increased by the port strike value (e.g. 50% more aircraft are involved in a port strike if you have the first "Base Strike" naval doctrine). Note that air wings on a port strike mission may get targeted by state-level "static" anti-air Anti-air (building).png.

Air supply mission

Available for: Transport plane

Wings with this mission Air Supply Mission.png provide supply to assigned ground troops if land-based supply is insufficient. Command points are automatically used for these missions and transport planes can be shot down. The amount supplied isn't much, even with 100 transport planes, so this method shouldn't be relied upon.

Multiple missions

Wings with multiple assigned missions will generally only perform the first applicable mission and only mission efficiency bonuses (e.g. from air doctrines) for that mission get applied. To perform multiple missions simultaneously, create multiple smaller wings and assign them individually.

Air combat

Air combat is simulated every eight hours (at 08:00, 16:00, and 24:00). Depending on the location and the time of year, this leads to a varying amount of combats happening at day or night. Each of the following phases is completed for all countries before the next phase begins.


The detection chance depends on multiple factors

  • Occupation: Occupying land in the strategic region enables spotting planes from the ground and yields a chance of up to 10% (when controlling the whole region).
  • Radar: Radar coverage yields up to 50% detection chance (at full radar coverage)
  • Air missions: Planes operating in the region yield up to 80% detection chance (with 3000 planes, non-fighters only counting half)
  • (above chances stack additively)
  • Night-time: reduces detection by 20%
  • Bad weather: reduces detection by up to 90%

Only this percentage of enemy planes will be visible. Even after detection, the visibility of planes can be reduced further, e.g. by the Infiltration Bombing doctrine (-50% visibility for strategic bombers). At most three times as many own planes can deal damage as enemies are visible, so good detection is important to fully utilize available air wings.

Damage and Disruption

Air wings sortie in descending order of air attack and agility against detected enemies, so fighters and heavy fighters will generally do most of the damage dealing. Bombers can also deal air damage when necessary though.

Fighters disrupt enemy non-fighter missions, 1 point of disruption per fighter. This value gets increased by up to +100% from fighters' speed (at 1500 km/h) and up to +100% from detection (stacking multiplicatively). This makes detection critical for disruption as it increases both the number of fighters acting against enemy bombers as well as the disruption effect of each individual one. Disruption is distributed among enemy non-fighter wings according to their visibility/size.

For damage dealing, the planes are allocated against enemy wings according to their visibility/size. The following components are considered in the damage calculation:

  • the attackers' air attack
  • the defenders' air defense
  • stats multiplier: the difference in speed divided by 1500 km/h plus the difference in agility divided by 100. This modifier is capped between -100% and +100% and then multiplied by 30%. For example a 1936 fighter against a 1936 tactical bomber gets a bonus.
  • carrier factor: 0.1 for normal and 5 for carrier combat
  • agility disadvantage: if the target has more agility, a penalty of up to -67.5% is applied. The maximum penalty is reached at an agility ratio of 1:2.5.

Equipment loss and escorting

Each point of damage received in the damage phase results in the loss of one airplane. Damage is rounded statistically, e.g. 1.2 damage received causes 1 plane to be lost in 80% of combats and 2 planes in 20% of combats resulting in 1.2 average losses per sortie. Fighters on escort/air superiority mission counteract the disruption that bombers received from the enemy in the disruption phase.

Non-fighter missions

Other planes perform their missions, such as close air support, strategic bombing etc. Disruption reduces the effectiveness of these missions. Wings may take additional losses in this phase from state, naval, or divisional anti-air.

Air superiority

Air superiority is the degree of dominance of your air force over an opponent's air force in a strategic region. Air superiority is provided by planes actively performing their mission and depends on their type as well. Each type of an air wing has a defined air superiority power value that describes how effective it is in domination of the sky (see table below).

Air Superiority Table
Aircraft Type Superiority Power
Heavy Fighter 1.25
Fighter, Carrier Fighter, Jet Fighter, CAS, Carrier CAS, NAV, Carrier NAV, TAC, Jet TAC 1.00
Strategic Bomber, Jet Strategic Bomber 0.01

The superiority power in the region comes from all of your (and your allies) active airplanes in that region. The more airplanes, the higher the value. Be aware that the value is also reduced (adjusted) with low region coverage. So remember to rebase your air wings to get the most optimal region coverage. Air superiority can also be adjusted by mission efficiency. Fighters on air superiority missions are generally the best way to get air superiority.

A region's air superiority is determined by comparing your adjusted air power (including allies) to the enemy's adjusted air power. This ratio is stated as a percentage and results in a color applied to a region (can be viewed using the Strategic Air map mode). The colors and interpretation of the colors is listed in the table below.

Air Superiority Region Color Table
Color Air Superiority Percentage Explanation
Red 0% - 30% enemy has air superiority
Yellow +30% - 60% contested region
Green +60% you (or allies) have air superiority
Air map mode screenshot showing different air superiority levels

Static AA Anti-air (building).png can also reduce air superiority in an air region. Each building level (maximum level 5) affects the air superiority multiplier by -1 (reference Defines NBuildings ANTI_AIR_SUPERIORITY_MULT = 5.0 -- How much air superiority reduction to the enemy does our AA guns? Normally each building level = -1 reduction. With this multiplier).

Every 50 points of air superiority advantage in a strategic region gives a +1% air support malus to enemy land combat defense and breakthrough. For this reason it is advised to hold air superiority as much as possible. AA inside divisions can reduce this penalty and potentially completely remove it. Air superiority also inflicts a malus to enemy movement.

Having Air Superiority in a sea region can increase the chance to spot enemy vessels (reference Defines NNavy DETECTION_CHANCE_MULT_AIR_SUPERIORITY_BONUS = 0.25) or to reduce enemy ship mission efficiency (reference Defines NNavy ENEMY_AIR_SUPERIORITY_IMPACT = -1).

Air superiority can also affect other air missions such as:


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

Skill Level Chance Fighter Ace Strategic Bomber Ace CAS, TAC, or Naval Ace
"Good" 0.9
  • +3% Air Attack
  • +3% Speed
  • +5% Agility
  • +5% Bomb Targeting
  • +3% Range
  • +5% Naval Targeting
  • +3% Ground Bomb Targeting
  • +5% Agility
"Unique" 0.4
  • +6% Air Attack
  • +5% Speed
  • +10% Agility
  • +10% Bomb Targeting
  • +6% Range
  • +10% Naval Targeting
  • +5% Ground Bomb Targeting
  • +10% Agility
"Genius" 0.05
  • +10% Air Attack
  • +8% Speed
  • +15% Agility
  • +15% Bomb Targeting
  • +10% Range
  • +15% Naval Targeting
  • +8% Ground Bomb Targeting
  • +15% Agility

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