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Air warfare consists of the deployment of air wings to Strategic Regions, where they can undertake missions targeting Production, Construction, Infrastructure, other Units, or in the case of naval and tactical bombers, naval units, ports, or convoys. 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 strategies.
- 1 Deployment
- 2 Air combat (fighters)
- 3 Air superiority
- 4 Aces
- 5 Close Air Support
- 6 Strategic Bombing
- 7 Naval Bombing (this information needs to be verified and edited)
- 8 Guides
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 requires service manpower, and can't be created unless there is enough available manpower.
Air wings can be assigned to an air region called "area" inside Hearts of Iron IV. An air region comprises a number of states or naval zones, and can cover a fairly large area, such as Northern France. Once assigned to an air region, one or multiple missions can be activated for each wing. A wing cannot be assigned to two or more regions at once. Most air regions cover only land or only sea, but some cover both. This can affect the type of mission that can be carried out. Air regions that include naval zones cover the same area as naval regions.
In Strategic Air map mode you can click anywhere on the map to display the air region view.
Once you create a new air wing it takes several days for the planes to arrive. The wing can be assigned to an air region and given missions immediately, but it will not carry out the missions until the planes arrive.
Air wing size can take any value between 1 and 1,000 planes. They must all be the same type of plane. For example, you cannot mix fighters and close air support in the same air wing. You can change the size of an air wing once it is deployed. An air wing has both a reinforcement level, and the current number of planes. If you increase the reinforcement level, then the current number will increase to match it, as long as there are sufficient stockpiled planes of that type to reinforce the wing. If there are not, then the reinforcement will take place once new planes of the correct equipment type are produced by your military production lines. You can also merge two or more wings of the same type of plane located in the same base, or split a wing into two new wings, each 50% of the size of the original wing. There is also a Reorganise option that allows finer control to move planes between two or more wings of the same type.
If you disband an air wing then all of the planes return to your equipment stockpile, and are then available to be deployed to other air wings.
An air wing can have an Ace which improves the combat stats of the wing. Air wings in HOI4 do not have commanders and cannot be renamed.
Air bases are state buildings, which can be constructed or repaired from the Construction screen.
Each air base on land can support up to 200 planes per base level without any penalties. The maximum air base level is 10, for a maximum of 2,000 aircraft. All models of planes can 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). The air base view above shows Kanto has a total capacity of 1200 planes (level 6 base), and there are currently 253 planes located there.
If the total number of planes is 250 in a level 1 base (capacity 200), then the air wings get a -50% penalty to their mission efficiency. If the total is 300 planes then there will be a -100% penalty.
Air bases can be damaged by strategic bombing missions. Damage will reduce the capacity the base can hold without penalty, until this is repaired. If you can inflict enough damage on enemy air bases to cause a large efficiency penalty, then you can effectively ground your enemy's air wings.
Overrunning By Enemy
If their air base is overrun 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. If the new air base is within range, then they continue to operate the same missions. Their mission efficiency will be adjusted accordingly. If the mission is no longer within range, then the planes will complete any current combat mission they are engaged in, then will go into Standby at the new air base. The player or AI can then give them a new mission.
A fleet with aircraft carriers can also operate as a floating air base. Carrier capable models are the only planes that can be based on aircraft carriers. The maximum number of planes allowed on an aircraft carrier fleet without any penalty is determined by the deck size of the carrier(s). This is much smaller than bases on land - ranging from a capacity of 45 (1922 base model CV) to 85 (1944 base model CV), and up to 31 higher with +5 deck size variants.
For a fleet to operate like an air base on land, then the fleet must be at anchor. If the fleet is patrolling, then the air wings are on a carrier mission. This means they only take part in naval combat with the carrier fleet. If the fleet is anchored then the air wings on the carrier(s) can be assigned to standard air missions covering a region, like air wings based on land. This can be very useful to provide air support for an amphibious invasion.
This is the same as 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. These wings can be assigned standard air missions in an air region.
Each Air Wing can be assigned to a single air 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.
The air wing view by default shows the name air region that the air base is located in, and the distance to that region, which will be 0 km. If you select another region then the name changes, and the distance to that region is shown. If the planes in an air wing have insufficient range to reach that region, then they will be hatched red. You will not be able to assign them to the region. If they can reach the region, but have insufficient range to cover it all, then they will be hatched yellow to warn you that there will be a mission efficiency penalty if you assign them to 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.
The air coverage percentage for planes which don't have sufficient range to cover the whole area of a region, is available from the air region view. An icon for each wing shows:
- Green if Mission Efficiency is 100%, which means that air coverage must be 100%
- Amber if Mission Efficiency is less than 100%, but over 50%
- Red if Mission Efficiency is less than 50%
The Mission Efficiency can be affected by air base capacity and weather penalties. The tooltip for an amber or red icon will confirm if the wing is unable to cover the whole region.
The lower the Mission Efficiency, the less successful the mission is likely to be, your air wings will do less damage to their targets and are more likely to be take damage, and maybe shot down by enemy aircraft and AA fire. Choosing an alternative mission or sending more planes may be considered, but the most important factor is the range from the region, and therefore the location of the air base that is used. All wings with early models of light frame planes (fighters, CAS and naval bombers) will have poor coverage if they are based outside of the region they are operating in, unless their base is very close to the border.
If you do not control any bases within a region that you are attacking, then you are at a considerable disadvantage to your enemies, who do. You 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 you can redeploy some fighters and CAS there. It might even be worthwhile if you capture a state without an air base to build your own level 1 base there as quickly as possible. That will allow you 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 capacity.
- Using carrier fleets might also be very useful if the region has a coast where you can (safely) anchor the fleet. Especially if the attack on the region is being carried out by 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 your 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 your fighters. But will give your enemy the Air Superiority bonus in combat.
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, sandstorms and blizzards being particularly bad. It may be advisable to put air wings on standby during such conditions.
|Type of Planes||Missions Available|
|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, but required for dropping paratroops|
- Close Air Support: Directly attacks enemy land units that are engaged in combat.
- Air Superiority: prioritizes attacking enemy fighters on their own air superiority missions, but also can escort your bombers and intercept enemy bombers. Gives a possibility of the Air Superiority bonus to land units in the region.
- Interception: attacks enemy bombers. Heavy Fighter range and survivability makes them suitable for bomber interception and escort. Interception missions never attack enemy fighters.
- Naval Strike: Attacks enemy ships at sea.
- Port Strike: Attacks enemy ships in port at a naval base. It does not attack the port facilities, the naval base can be damaged only by strategic bombing.
- Strategic Bombing: Attacks enemy constructions, including factories, infrastructure, AA, naval bases and air bases etc. If air bases are bombed then there is a chance to destroy some enemy planes based there.
- Kamikaze Strike: Special mission unlocked with the Japanese national focus or with Ideological Fanaticism from the generic national focus tree. Prioritizes inflicting maximum damage against sea targets, at the cost of aircraft.
Transport planes have no missions. They are required to execute paradrop plans. Unlike in HOI3, they are not used to drop supplies in version 1.1. This feature may be added in later versions.
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. Fighters with both air superiority and interception missions probably only ever carry out air superiority. It is more efficient to have two wings each ordered to execute one of two mission types than have both of them ordered to execute both mission types.
Naval bases are located within provinces on land. Port strikes can therefore only take place in a region which covers land. The port strike mission will be ignored if it is given to a wing operating in an all-sea region, like the Yellow Sea. Some regions mainly cover the sea, but they may also include some islands with naval bases, like East China Sea which includes Taiwan. The opposite is also the case - a naval strike can only target fleets which are at sea, so such a mission would be ignored if given to a wing which is assigned to an all-land region like Northern China. Finally, close air support missions and strategic bombing would be ignored if given to a wing in an all-sea region. In some parts of the world you have to be careful to check which region a naval base is located in, otherwise you could be giving wings missions that will be ignored, the interface does not warn you this is the case.
Mission Schedule, Rest, and Day/Night cycle
Missions take 7 hours in the air and a plane can only do two missions in a row. After that, it must rest at the air base for at least 4 hours before it can be sent into combat again. Its mission schedule depends on whether it is set to Day missions only, Night missions only, or Day & Night missions. Day is from 09:00 to 00.00 on the game clock. Night is from 01:00 to 08:00. At night, it is 20% harder to detect planes and bombing has -50% efficiency but air combat is otherwise unaffected.
- Day: Enters first mission at 09:00 and leaves second mission at 23:00, then rests until its next day mission.
- Night: Enters combat at 01:00 and leaves at 08:00, then rests until its next night mission.
- Day & Night: Enters a 19 hour cycle of performing two missions, resting, and repeating until ordered to stop.
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 land-based air wings, or CV-based planes taking place in air combat, all rest for 4 hours after a mission, then they can be sent on their mission again. CV-based planes must rest for 6 hours between strikes within naval combat.
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%).
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.
- 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.
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. Note that aircraft variants created in the production interface by using Air Combat Experience can change statistics and therefore combat effectiveness in powerful ways. (see the guide linked below)
- 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.
- 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.
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 Ace||Bomber Ace||Ground Support or Naval Ace|
|"Good"||0.9||+3% Air Attack
|+5% Bomb Targeting
|+5% Naval Strike Targeting|
+3% Ground Bomb Targeting
|"Unique"||0.4||+6% Air Attack
|+10% Bomb Targeting
|+10% Naval Strike Targeting|
+5% Ground Bomb Targeting
|"Genius"||0.05||+10% Air Attack
|+15% Bomb Targeting
|+15% Naval Strike Targeting|
+8% Ground Bomb Targeting
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.
Strategic bombing damage is about 120 damage per attack cycle for ~0.3 buildings destroyed. This damage appears to be distributed evenly among all the buildings (forts, industry etc.) in the air region without regard to the number of air wings presents.
Naval bombers and close air support can attack enemy fleets that are in the open seas (not in a port). This attack is called a "naval strike."
Naval bombers, close air support, and tactical bombers can attack enemy fleets that are moored in a enemy port. This a attack is called a "port strike."
The bombing missions are affected by both air and naval doctrine.
The naval doctrines "Trade Interdiction" and "Base Strike" give both land or carrier based air craft (naval bombers, close air support, and tactical bombers) "naval targeting" bonuses.
Trade Interdiction gives a +20% total naval targeting bonus.
Base Strike gives a +40% total naval targeting bonus.
The ingame mouse over explanation of naval targeting is "Modifies our planes' ability to target their objectives when executing naval strikes."
Similarly, air doctrines give bonuses to naval attacks. The air doctrines "Battlefield Support" and "Operational Integrity" give both land or carrier based air craft (naval bombers, close air support, and tactical bombers) a +10% "Naval Mission Efficiency" bonus. This +10% naval mission efficiency bonus is earned upon completion of the "Torpedo Strike Torpedo Tactics" found in both "Battlefield Support" and "Operational Integrity." The ingame tool tip definition of Naval Mission Efficiency is "improved tactics for planes doing naval bombing or port strikes resulting in increased ability." One possible interpretation of this is that the significance of Naval Mission Efficiency is that it grants naval bombers, close air support, and tactical bombers an improved (+10%) chance to complete a naval strike or port attack.