HoI4 Air Superiority and CAS Guide

Air power is the most misunderstood multiplier in Hearts of Iron IV. Players who ignore it lose battles they should win and blame their templates. Players who overbuild it starve the army of rifles to feed a thousand-plane air force that never finds the enemy. Both mistakes come from the same place: the air war runs on two stats the UI barely explains, and the thing you are actually fighting for is a debuff, not a kill count.

Get three ideas in the right order and everything else clicks. First, air superiority exists to halve the enemy's defense and breakthrough — that is the product, and shooting down planes is only how you pay for it. Second, your air force fights at the size of its two invisible caps, mission efficiency and detection, not at the size of its roster. Third, close air support is a luxury that prints value only under a sky you already own. The rest of this page unpacks those three ideas into decisions: what to build, how to design it, where to put it, and what to do when the enemy owns the sky instead.

What Air Superiority Actually Does

The kill feed is a distraction. When your fighters own a region, the game applies a debuff to every enemy division under that sky: reduced defense and reduced breakthrough, scaling up to minus fifty percent. Open a defending division's tooltip during an attack and you can see it directly — something like minus forty-three percent defense from enemy air superiority. Halving an army's defense before your tanks even cross the river is what wins land wars. Everything else about air power is logistics for delivering that debuff.

This reframes the entire air war. You do not need to annihilate the enemy air force; you need to hold the sky over the battles that decide the campaign. A lopsided kill count with no ground effect means you are fighting in the wrong zone. A modest fighter force parked over your main offensive axis, painting the map green, is doing more for the war than a glorious turkey shoot over a quiet front.

Air superiority also gates the special operations. Paradrops require at least seventy percent superiority over the drop zone. Port strikes require the enemy to be at thirty percent or below. Nuclear strikes, late game, demand seventy-five percent. The game shows these requirements in the mission interface itself — read them there before committing rather than trusting any fixed number. Green air quietly enables your navy too, supporting ships in battles under the contested sky.

The last consequence is the one new players miss: close air support scales with all of this. CAS value, and the doctrine bonuses that amplify it, rise with how much of the sky you control. Under green air, CAS is a force multiplier on top of a multiplier. Under red air, the same wings are an expensive way to lose planes. There is no such thing as "CAS to compensate for losing the air war" — the two do not combine that way.

The Two Invisible Caps on Your Air Force

Your air force has two sizes: the one in the production screen, and the one actually fighting. The second is always smaller, and it is set by two caps that the UI buries. Most "my air force doesn't work" problems are one of these two, not the plane design.

Cap one: mission efficiency — what share of your planes can take off. Nine hundred fighters at sixty-nine percent efficiency is a six-hundred-twenty-fighter fight; the rest sit on the runway. A wing builds efficiency up from zero when first assigned to a region, so low numbers on day one are normal, not a bug. What is not normal is staying low, and the usual suspects are four: your range circle does not fully cover the air zone (every uncovered slice costs you), the air base is overcrowded past its limit, the weather is bad, or you are out of fuel. Deploying more ground crews adds ten percent efficiency even on a wing already at one hundred. One warning: the zone's average mission efficiency lies. Two idle transport wings dragged into the region will tank the average while your fighters are fine. Always drill into the per-wing numbers before trusting the zone summary.

Cap two: detection — what share of the enemy you can see. You cannot shoot planes you have not spotted, and detection decides how many get spotted. The math is brutal and linear. Say you have one hundred fighters and twenty-five percent detection: you reveal twenty-five enemy planes, and only about seventy-five of yours can engage — three times the spotted count. Scale your force to a thousand planes and the cap barely moves; a blind thousand-plane air force fights at seventy-five. Detection comes from controlling the ground below (ground spotting, roughly ten percent, and the enemy gets it when fighting over their own territory), from your planes' range covering the zone, from planes physically in the area, and from radar. Night cuts it. There is one exception that matters: bombers on a bombing run are far easier to engage, so even a low-detection force can get its fighters into combat against enemy bombers. Detection is mainly the stat that decides fighter-versus-fighter trades.

When the air war looks lost, run the same diagnostic every time instead of guessing. Glance at average mission efficiency, then check each wing individually. Look at detection if fighters are not trading. Count active fighters and AA guns on both sides. Read the air superiority bar against the thresholds you actually need. Then open the airbox details — the summary only covers the last eight hours, while the details show the whole war: fighters lost on each side, bombers lost, trains and tracks and trucks destroyed, buildings bombed, ships sunk. Twelve of your fighters lost against forty-three of theirs means you are winning, even if the last eight hours felt quiet.

Fighters First: What Wins the Air War

Fighters make or break the air war, and they should spend most of the game on the Air Superiority mission. Everything else you fly — CAS, bombers, naval strike — operates on the credit your fighters extend. So the first question of any air plan is never "what CAS do I build" but "can my fighters win the trade." The trade itself comes down to a short, stable hierarchy of stats.

Air attack and air defense decide who trades better, and they outrank everything else. Air attack is your raw damage output and the priority stat for fighters specifically. Air defense is the most important defensive stat in the game right now: it divides incoming damage so fewer planes die, it reduces the damage your wings take from ground AA, and it decreases disruption, which is what lets your bombing and ground-support missions actually complete. A plane that survives its sorties flies more of them; survivability compounds.

Speed is the best offensive stat after raw air attack. A wing's maximum speed adds a flat damage bonus, and being faster than the enemy adds a second one on top — a seven-hundred-kilometer-an-hour fighter beating up a five-hundred-kilometer-an-hour fighter gets paid twice. Speed also lets you choose fights. Under the hood, every point of thrust over weight is worth three kilometers per hour of max speed, which is why module weight is a design tax; if weight ever exceeds thrust the plane cannot take off at all, and the designer will refuse to let you save it.

Agility is no longer king. Old guides treat agility as the defining stat, and it has since been massively nerfed. It still reduces damage taken, but only its value relative to the enemy matters: keep it roughly level with the aircraft you expect to fight and stop thinking about it. Far below the enemy and you get destroyed in mass; roughly even and it is a minor stat. Do not design around it.

Stat	What it actually does in combat	Who needs it
Air attack	Raw damage in air-to-air trades.	Fighters — the offensive half of the trade.
Air defense	Divides incoming damage, cuts ground-AA losses, reduces mission disruption.	Every plane that expects to be shot at, which is all of them.
Speed	Flat damage bonus, plus a second bonus for being faster than the enemy.	Fighters — best offensive stat after air attack.
Agility	Reduces damage taken, but only relative to the enemy's value.	Keep it roughly level with the opposition; do not stack it.
Range	Decides whether you fight at all.	Everyone — it silently gates every other stat.

Two levers outrank any stat line. The first is technology: being ahead in airframe and engine tech is the single best way to win an air war, and it beats most other factors — a tech-leading air force trades favorably even with mediocre designs. The second is wing experience, which has five levels and a gap between them large enough that green wings simply get slaughtered. Never ship brand-new wings straight to the front. Run them on Pilot Exercises in an air zone the enemy cannot reach until they hit the third level, Trained; combat then pushes them the rest of the way. The early days of a war are when air experience is most defining, so train before the shooting starts.

Designing Planes That Outlive Patches

Specific plane builds go stale every balance pass, so the durable skill is designing to principles and reading the live numbers off the designer yourself. Six rules cover almost every airframe decision in the game.

1. Range is the first stat, not a nice-to-have. If your range circle does not fully cover the combat region — all of Poland, all of Egypt, the whole Ukrainian stretch — the wing pays efficiency penalties for every uncovered slice, and a superior plane that cannot reach the fight loses to an inferior one that can. Range beats air defense: a plane with slightly less defense but enough reach wins the battle the other plane never makes. Fix coverage with drop tanks, extra fuel tanks, or simply more airfields closer to the front. Extra fuel tanks shave a little air defense; accept the trade.

2. One engine on a light airframe, always. A second engine jumps production cost by well over half and costs you agility and thrust for almost nothing in return. If you genuinely need two engines, you are describing a medium airframe — build that instead. Light frames are the workhorses of the air war and should stay cheap.

3. Quantity beats quality when resources are scarce. Tons of planes that are merely okay beat a few great planes that never move the needle. A small elite air force loses planes it cannot replace and loses the efficiency-of-numbers fight; a large adequate one holds zones. Design to what your economy can sustain, then stop optimizing.

4. Match your CAS and naval bombers to your fighter range. Wings of different ranges cannot share the same airfields and cannot all operate over the same region without debuffs. Designing your CAS to the same reach as your fighters lets the whole air group base together and cover the same front — a small decision that removes a permanent operational headache.

5. Let your resource map choose the defensive modules. Self-sealing fuel tanks add air defense and are strictly better than the alternatives — worth their rubber cost whenever you can afford it, with drop tanks as the cheap fallback when you cannot. Armor plates also add air defense and are the rubber-free route. European nations are rubber-poor and must budget this; Asian majors like Japan have rubber and can seal everything. The reverse problem is aluminum: the "no strategic materials" module can crater air defense — from nine down to three, for example — while cutting aluminum cost to one, and for an aluminum-starved nation it is still correct. Tons of planes at three air defense beat zero planes at nine.

6. 1939 is the power spike; the late tiers mostly are not. The second generation of airframes — the 1939 fighter and the 1939 CAS — is massively better than the 1936 versions, and the fighter in particular is arguably the best cost-efficient design in the game: it destroys AI-made planes and is safe to keep producing for the entire run. With those two designs you genuinely do not need anything else for the rest of a campaign. The advanced small airframes and engines that follow cost more than the stats they return, and the research is usually better spent elsewhere. The one late-game exception is the supersonic small airframe behind the special-project system, whose stats dwarf everything else — a real endgame prize if your research economy can reach it. Airframe slots grow as the tiers advance (two weapon slots on the 1936 frame, three on the 1939, four on the 1944), which is why later planes can carry more guns without sacrificing defensive modules.

Role	Airframe	Priorities	The trap to avoid
Fighter	Small	Air attack, air defense, speed, then enough range.	Two engines on a light frame — build a medium if you need them.
CAS	Small	Air defense first, range matching your fighters, ground attack last.	Chasing air attack — small differences barely move ground damage.
Naval bomber	Small; carrier-based if you have decks	Surface detection, torpedo tech as it unlocks, armor plates.	Land-based sorties — carrier wings are several times more efficient per sortie.
Heavy fighter	Medium	Range and durability; free modules into fuel or turrets.	Buying them for a European war, where range is rarely the bottleneck.
Tactical bomber	Medium	Flexibility: CAS, port strike, logistics strike, strategic bombing.	Expecting it to CAS as well as a dedicated plane — it does not.

Two production tricks round this out. Countries that start with cannons — Germany and the Soviet Union, for instance — can run an offensive early fighter variant that trades range for a large air attack jump, a real edge in the opening air war. And when you want to upgrade a module fleet-wide, the Convert button refits planes already in your stockpile for a fraction of the raw resources: design a base variant and an upgraded one, produce both, then convert the older into the newer. Two catches: conversion only eats planes sitting in the stockpile, so if you deploy everything to the front it silently stops; and you must balance factory allocation between fresh production and conversion by hand, or one outpaces the other.

The CAS Question: How Much Gun Is Too Much

Once the fighters are winning, CAS is where the air war starts paying rent on the ground. The first thing to internalize is that the mission itself carries most of the value. Even the cheapest, weakest CAS configuration delivers a ground-attack bonus on the order of a quarter to a third just for flying the mission — so a modest wing that shows up is already doing real work, and the design question is how much extra damage you want to buy, and at what cost.

There are three philosophies, and testing them head-to-head reveals which is the default. The first maximizes agility and air defense and skimps on ground attack: the cheapest planes, the fewest losses, the least damage. The third goes all-in on ground attack — a twin-engine frame with an anti-tank cannon and heavy bomb load — and hits the hardest per plane while costing nearly double and bleeding airframes faster than anything else. The middle road takes one step down from maximum survivability, keeps strong air defense, and carries a serious ground-attack payload.

The honest way to compare them is not damage per plane but damage per factory. Fix a total production budget, divide it by each design's per-plane cost to get the fleet size, and compare the troop damage over the same stretch of days. The plane designer shows you both numbers side by side — ground attack and IC cost — so you can always rerun this comparison yourself against the live values in front of you. Run that test and the middle design deals roughly twice the troop damage of the agility build for about ten percent more production cost, while the max-gun design does the most damage of all but loses the most planes at a price per airframe that makes every loss compound. The agility build's survivability, in other words, buys far less than it appears to: you save a handful of planes and forfeit half the ground damage.

One module mechanic explains why the middle road wins. Rocket rails add ground attack without reducing agility on CAS missions at all — they are free, and the only reason to skip them is to free a lower slot for a defensive module like armor or air defense. Trading one rail for survivability is exactly the exchange the middle design makes, and it is almost always worth it. Meanwhile, do not chase air attack stats on CAS the way you would on a fighter: unless you are flying a heavy bomber, small differences in air attack barely change ground damage, and the same module slot spent on air defense keeps the plane alive to fly another sortie. Survivability is the CAS stat.

Operationally, the three philosophies are not rivals — they are a sequence. Open the air war with cheap, survivable CAS to keep losses down while your fighters win the sky. Once you own it, bring the heavy max-ground-attack design out for the decisive encirclement axis, where finishing the pocket a few days faster is worth the IC bleed. Deploy it like a scalpel, not a blanket. If you run a CAS-heavy air force as a major, the Battlefield Support doctrine is the amplifier: it adds a large ground-support bonus — on the order of plus sixty-five percent — that scales with how much of the sky you hold. That scaling is the whole doctrine in one line: monstrous under green air, worthless under red. Never take it expecting to lose the fighter war.

Anti-Air: What Protects What

Here is the misconception that costs more divisions than any other: anti-air buildings do not protect your troops from CAS. Ground AA — the structures tied to infrastructure — and the support AA company inside a division are two different tools that players constantly confuse, and only one of them does what you think.

Ground AA does three things, none of which is saving your infantry. It defends your buildings, so strategic bombing and logistics bombing of a well-covered target gets expensive and demands a calculated decision. It slightly reduces enemy air power in the region, tipping the air-superiority balance — small in a lopsided fight, but capable of swinging a close one. And it can shoot down planes flying strategic bombing, port strike, or air supply missions. What it never does is touch close air support or fighters. CAS is immune to ground AA structures entirely.

The thing that actually counters CAS is the support anti-air company in the defending division. It does double duty: it reduces the damage the division takes from CAS, and it inflicts losses on the attacking wings. The size of the effect is what makes it non-negotiable. Against divisions with no support AA, enemy CAS deals roughly three times the damage, and encirclements close noticeably faster — about a fifth quicker in side-by-side testing. Support AA is the single cheapest counter to close air support in the game, a support-company slot that blunts an entire enemy air arm. The division templates guide covers where it fits in a template; the rule of thumb is that any division expected to hold under enemy sky wants it.

AA source	What it actually protects	What it will never do
Ground AA (buildings, infrastructure)	Buildings against strategic and logistics bombing; tips regional air superiority; can kill planes on strat bombing, port strike, and air supply.	Protect divisions from CAS — it does not touch close air support at all.
Support AA company (in the division)	The division itself: cuts incoming CAS damage and shoots down the attacking planes.	Replace an air force — it is insurance, not parity.
Ship AA	The fleet against naval bombers, averaged across the screen.	Anything ashore.

One environment note: in single-player the AI rarely stacks AA into its divisions or onto its ships, so CAS often runs nearly unopposed and support AA can feel optional. In multiplayer, competent opponents stack it everywhere, and the same CAS doctrine that felt godlike against the AI runs into a wall. If you are transitioning to human opponents, respect the difference — your air wings will take losses they never used to, and divisional AA on your own spearheads stops being a luxury.

Running the Air War: Bases, Wings, Doctrine

Good designs deployed badly lose to mediocre designs deployed well. The operational layer — where wings sit, what priority they hold, how you train and reinforce them — is the part most air guides skip, and it is where campaigns are actually won.

Bases and range come first. The chain is simple: an air base, its air menu showing only the planes in that single base, and missions assigned per air zone. Deploy wings as close to the target zone as possible; a range circle that barely clips the edge of the region pays major efficiency costs for the uncovered area, and the fix is usually moving airbases forward as the front advances rather than designing longer-range planes. Do not let a base exceed its capacity — overcrowding is a silent efficiency killer, and splitting wings across nearby airfields solves it. Managing many bases is genuine micro; do not be afraid to pause and do it properly.

Priority settings decide who gets the good equipment. Each wing sits at one of three priority levels. High-priority wings get reinforcements first and receive the better replacement designs; reserve wings get whatever is left and wait longest. The classic use is a two-front air war: as Germany, set the fighter wings facing a strong enemy air force to High and the wings facing a barely-built one to Reserve, so your limited production flows where the fight actually is. The Germany first campaign guide shows this in the context of a full war plan.

The visibility trap is the one operational insight that changes how you fight contested zones. The moment you run ground-support missions in an air zone, every fighter you have there becomes permanently visible to the enemy. Detection is normally a two-way fog; CAS lifts it for you, unilaterally. So in a heavily contested zone, the winning move is often to pull CAS off entirely and fight fighters-only until you win the trade, then re-add CAS once you control the sky. If the enemy runs CAS and you run only fighters, you hold the visibility advantage and out-trade them. This is why "just add more CAS" is so often wrong in a contested zone — it can be the very thing losing you the fighter war.

Aces, weather, and upkeep. Aces generate probabilistically from missions that sink a ship, down a plane, or bomb a building, and come in tiers — Good, Unique, Genius — each assignable only to the matching wing type. When you roll a Unique or Genius ace, assign it to a wing and set that wing to the elite reinforcement setting so it draws the best equipment and maximizes the bonus; remember an ace can die when a plane in their wing is shot down, so do not spend geniuses carelessly. Weather can dramatically cut mission efficiency and combat performance, which is why all-weather advisors in the officer corps turn a universal penalty into a private advantage. On upkeep: a wing of a hundred planes with a fuel cost of 0.2 drinks twenty fuel a day, so a large air force is a real fuel commitment; and reliability only governs rare air accidents, so keep it above roughly sixty percent and stop investing past that. Wings cap at a hundred planes each.

Doctrine and air command are where the bonuses get large. Pick the doctrine to match the air war you expect, not the one that sounds best on paper.

Doctrine	Built for	Pick it when
Strategic Destruction	Fighters	You are on the offensive and the enemy will not build many bombers. The safe default for non-air powers and for multiplayer, with more air superiority, mission efficiency, and fighter agility.
Battlefield Support	CAS	You are a major that expects to hold green air. Its large ground-support bonus scales with your air control — killer in single-player, worthless under red air, and its fighters are weaker than the other trees'.
Operational Integrity	Interception	The enemy is bomber- or CAS-heavy. Their escorting fighters are already visible, so the interception bonus makes you outrageous against a mission-dependent air force.

For spirits, the early standout is the research bonus on airframe types — fifty army experience to rush your second- and-third-tier fighters is one of the best spends in the game — alongside the spirit that cuts air doctrine cost and reduces accident chance. Avoid the daily-XP spirit early; it takes on the order of five hundred days to pay back. And for Air Command, take Centralized Control: a flat mission-efficiency bonus for every wing plus a detection bonus, the one command choice you should essentially always take. New wings should be trained to the third experience level before they see combat, as covered above — the experience gap is large enough that doctrine and aces cannot rescue a green wing thrown into a contested zone.

When You Cannot Win the Sky

Most countries cannot outproduce a major in the air, and that is not a lost campaign — it is a different campaign. The mental model does not change: you still want the debuff over the battles that matter. You simply stop trying to own every sky and start choosing which one sky is worth owning.

The recipe has five moves. First, concentrate everything on one decisive air zone and accept red air everywhere else; a small air force spread across five fronts matters nowhere, and the same force concentrated can genuinely contest one. Second, put support AA companies in every division that must hold ground or take part in an attack — under enemy sky this is the difference between a division that bends and one that breaks, and it kills enough enemy CAS wings to slow their whole air arm. Third, attack in narrow windows and on narrow fronts; broad offensives under red air are how minor nations bleed their armies dry. Fourth, use the weather: bad conditions ground CAS and cut efficiency on both sides, so a well-timed offensive in a storm is the poor country's green air. Fifth, do not build CAS you cannot escort — under red air it loses planes without delivering damage, and those factories should have been fighters or AA.

If the enemy air force is built around bombers and CAS rather than pure fighters, you have one strong asymmetric answer: Operational Integrity doctrine and the interception mission. Bombers on a mission are easy to engage even with modest detection, and the interception bonus lets a smaller air force punish a larger mission-dependent one far above its weight. You do not need superiority to make their bombing campaign unaffordable.

One thing to deliberately not build: a strategic bombing force in single-player. It is the weakest air investment for a conquering nation, because you advance fast and occupy the provinces you are flattening — you end up bombing your own future infrastructure. Strategic bombing earns its keep in multiplayer, where someone else has to rebuild what you leveled. Against the AI, those factories should be fighters, CAS under your own sky, or the army itself. Air power is a multiplier on a land plan; if the battle plan and the supply line behind it are broken, no amount of sky fixes it.

FAQ

Next Reads

• HoI4 Beginner Guide — where the air war fits in a first campaign, and what to learn before it.
• HoI4 Division Templates Guide — support AA companies and templates that hold ground under enemy sky.
• HoI4 Battle Plans and Frontlines Guide — turning green air and CAS into encirclements that actually close.
• HoI4 Supply Guide — fuel for a large air force, logistics strikes, and forward airbases that keep wings in range.
• HoI4 Germany First Campaign Guide — the classic two-front air war, wing priorities, and CAS-driven offensives in practice.