Hearts of Iron IV
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 from the perspective of each country before the next phase begins.
Detection, damage and disruptionEdit
In this phase, own air wings will try to attack the enemy, both by directly damaging them and, in the case of enemy ground missions, disrupting them. Enemy countries are any that this country ( or the host country of air volunteers) is at war with. The prerequisite for attack is the ability to detect the enemy.
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. The number of visible planes can be further modified:
- If the enemy side includes both ground missions and superiority fighters, the latter will be fully visible. The fighters and bombers don't need to be from the same enemy country.
- Regular bombers on strategic bombing mission and carrier-based bombers can reduce their visibility with the "Strategic bombing visibility" modifier (Infiltration Bombing doctrine: -50%).
- Planes on close air support mission are twice as visible.
- Planes on port strikes are ten times less visible.
At most three times as many own planes can attack as enemies are visible, so good detection is important to fully utilize available air wings, especially when the enemy has fewer planes.
If the country does not send ground missions, enemy intercept missions will be ignored as targets. Likewise, if the enemy has no ground missions, own interceptors will not attack. Carrier fighters actively take part in air combat (as superiority fighters) and all types of enemy carrier planes are available as targets if their carrier is in a naval battle. Wings on both sides produce 0.075 country air experience per plane for their respective countries. This means an air force getting attacked by multiple countries gets a multiple of experience.
All wings considered for attack gain 0.4 wing experience. 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. If enough enemies are detected, bombers can also deal air damage though.
The planes of each sortieing wing are allocated against enemy wings proportional to their visibility (against all wings for damage and only against ground missions for disruption). The following components contribute to the final damage value:
- 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 6 for carrier combat (if both the attacker and defender are carrier wings)
- agility disadvantage: if the defender 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.
The following components contribute to the final disruption value:
- attacker's speed effect: attacker's speed divided by 1500
- detection chance
- carrier factor: 4 for normal and 8 for carrier combat (if both the attacker and defender are carrier wings)
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.
Equipment loss and escortingEdit
Fighters on escort/air superiority mission counteract the disruption that bombers received from the enemy in the disruption phase. Bombers of allied countries don't get escorted. The following components contribute to the escort's disruption reduction:
- base: 2
- speed factor: speed divided by 1500
- agility factor: agility divided by 100
- attack factor: attack divided by 100
This ratio gets removed from the received disruption of all bomber wings. The number of active escort planes is not recalculated for this phase and is used as the last country in the previous phase left it in, causing some countries to have arbitrarily worse escort efficiency.
If a wing lost at least one plane and has an ace, there is a chance that they die as a result of the air combat. The chance is the number of lost planes times 0.001 times 0.1 plus 0.003. Due to rounding issues this is effectively just 0.3% unless the wing loses ten or more planes in a single sortie.This means an ace can be expected to survive 230 sorties with losses.
Each point of damage received in the previous 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.
Other planes perform their missions, such as close air support, strategic bombing etc. They gain 0.28 wing experience. Disruption reduces the effectiveness of these missions. Wings may take additional losses in this phase from state, naval, or divisional anti-air.
All ground missions except para drop and mine planting/sweeping require the selection of a specific target. If multiple missions are selected, they are tried in the following order:
- close air support
- strategic bombing
- naval bomber/kamikaze
- port strike
- air supply
Only the first category that produces a valid target is used, but a single wing can handle multiple targets within the same category in one sortie. It is not necessary to split up wings to support multiple land combats for example. But a large naval bomber wing can for example not send any remaining planes on a port strike when another part of the wing executed a naval strike.
Night time's "Ground Bombing Targeting" modifier (-50%) causes a corresponding probability of the wing being unable to find their target. They are still subjected to state AA.
Strategic bombing, port strike and air supply missions are affected by state anti-air (AA).
The probability that a damage event occurs (C) and the number of planes destroyed (D) depend on the following components:
- damage base chance: 10%
- hit chance modifier: the "Static Anti Air hit chance factor" modifier (three radar technologies provide +20% each)
- a random number R between 0.0% and 100.0%
- damage factor: 0.8
- anti-air factor: for air supply missions, the AA value of their target's state (even when that state is friendly) divided by the maximum AA level (5). For the other two mission types, the average AA level in enemy states in the strategic region, divided by the maximum AA level (5).
- effective number of planes
- damage modifier: the "Static Anti Air damage factor" modifier (+10% each from anti-air 2 and 3 technologies)
- air wing's defense stat
If R is smaller than C, a hit occurs with the following damage (in number of planes destroyed):
Or averaging the random number to :
Small bomber wings and especially strategic bombers (having high air defense) will be frequently affected by the minimum-one loss.
Disruption damage factorEdit
The ground mission wing can reduce any disruption left over after the escort phase further using its own stats. Finally the disruption produces a damage factor that scales the damage the mission can actually do. It uses the following components:
- disruption: value after the escort phase
- defense factor: air wing's defense divide by 200
- attack factor: air wing's attack divided by 200
- speed factor: air wing's speed divided by 1500
- air wing's number of planes (not reduced by mission efficiency)
The value that gets reported as "Planes disrupted" in the statistics of an air region is accumulated over all missions and sorties in the time frame.
Guided missiles always have a disruption damage factor of 100%, ignoring any disruption applied against them.