Effective Use of Airpower

Overview

Aircraft in Hearts of Iron 2 are extremely powerful when used effectively: they can decimate enemy Navies and destroy enemy Armies. An effective use of airpower requires a considerable amount of research and aircraft construction: half-hearted attempts to create an air force will not be effective.

There are four types of bombers in HOI2:

There are three types of fighters in HOI2:

Finally, in a category of its own, there is the Transport Planes (TRA). For technology requirements for these, see the Aircraft_Tech_Tree .

Version Changes

HOI2: Air combat in the original HOI2 game was considerably flawed. The AI would send aircraft on suicide missions, and literally waste its most valuable aircraft for no tactical nor strategic gain. Meanwhile, Naval Bombers were ridiculously overpowered and could single handedly wipe out entire navies.
DD: Air combat AI was significantly improved. Escort fighters became brigades. Naval Bombers were weakened.
ARMA: Air combat AI was again improved. Aircraft take much more damage by enemy fire than in previous versions of the game. That means more micromanagement as you really don´t want your planes to attack larger enemy stacks.

Strategy

This diversity of options makes it nearly impossible for any nation to master all aircraft technologies, or build sufficient quantities of aircraft in all fields. Therefore, it is necessary to choose areas of specialization, contingent on your overall war strategy. Two sets of aircraft share technology doctrines, making them popular choices: Fighters and Interceptors; and Tactical and Naval Bombers.

For major nations, the choice in Bombers is divided three ways, and only two options can effectively be pursued. Most players choose TAC/NAV & CAS, and ignore STR:

Tactical & Naval Bombers
Close Air Support Bombers
Strategic Bombers

Airfields

Building CAS, TRA, or FTR aircraft is typically best served by building new airfields near expected fronts for the aircraft to be useful beyond the initial front early in the war. Germany, for example, must build up the Polish border provinces to house CAS aircraft prior to Fall Weiss. Building up along the frontier of the Low Countries and France will allow Germany to use CAS as an integral part of the attack, shortening battles, speeding up conquests, and in the end reserving manpower and organization for more rapid movement around the end of the Maginot line. The Soviet Union has a severe lack of airbases, and requires considerable construction efforts to create an effective infrastructure for air power.

Air Defense

A total of five factors can be used to provide an extremely strong air defense:

Interceptor "umbrella": Interceptors on Air Superiority missions covering each major interior region of your nation.
Fighter "barrier": Fighters on Air Superiority missions that provide a defensive "front-line".
Anti-Aircraft: To assist fighters and interceptors, anti-aircraft installations are very effective
Air Bases: Any air engagement over an airbase provides your aircraft with combat bonuses
Radar: Any air engagement over an airbase provides your aircraft with combat bonuses

Air Superiority

Air Superiority is not merely a defensive tactic. While extreme defensive measures can be successful in achieving air superiority, offensive measures can produce the same or better results. Considering that the intent of Air Superiority is to remove your enemy's ability to put aircraft in the air at all, offensive operations are necessary. This requires a coordinated effort by your air forces to not only repel enemy aircraft, but also damage the enemy's infrastructure for those aircraft. This is important because most air combat (in DD & ARMA) will only reduce the org and cause slight damage to attacking aircraft. Those aircraft will then retreat in order to repair. Actual destruction of aircraft is quite difficult and rare (in DD & ARMA).

Strategic bombers are the best weapon for attacking enemy infrastructure, and perform three vital missions:

Installation strikes to reduce the effect of AA;
Runway cratering to reduce the strength of airfields;
Logistical strikes to reduce province infrastructure -- which means airfields and AA will take longer to come back to normal.

Once air superiority has been achieved, periodic Strategic Bombing runs are necessary to maintain supremacy. This method, though expensive, can be used to achieve complete air dominance over an enemy.

Strategic Examples

Germany: As a nation, Germany relies upon the strength of their ground forces, very specifically their armor and fast attacks, to conquer territory and integrate it quickly into their war machine to fuel further conquests. A large STR force is absolutely antithetical to this approach. Reducing infrastructure and IC of provinces you're going to conquer slows your advance and lengthens the amount of time it takes to integrate the province into your empire's production machine. The clear choice for Germany is CAS/TAC.

Great Britain: Having the sea as a wall, Great Britain is in a position that massive land combats are not to be expected. Until the aid of the United States comes into the war, the UK will not be able to win an extended land campaign against a Germany set to defend against it. The best defense of the Home Islands is making certain that Germany cannot mount an attack. Being dependent upon overseas sources for your industrial materials means that you will be vulnerable if the Germans should cut your supply lines. Large land forces garrisoning all the possible landing beaches in Great Britain can be hard on your TC, leaving your overseas holdings vulnerable to conquest. Shutting down the immediate threat of Germany is your number one goal. TAC/STR is clearly the choice for Great Britain.

Tactics

Ultimately, the Air Force is only useful to the extent that it assists in the broader war effort, which generally means capturing provinces. In the land war, a complete/ideal use of the air force would be conducted like this:

An Interceptor wing flies over your own forces, protecting them from enemy bombers
A fighter wing flies over enemy territory, attacking enemy interceptors to clear the air for your own aircraft
Strategic Bombardment attacks behind enemy lines, weakening IC and province infrastructure of the soon to be retreating forces
Tactical Bombers conduct interdiction missions on the enemy lines as your main army attacks, helping to rapidly reduce enemy organisation
As the retreating enemy falls back into a province with greatly reduced infrastructure, your Close Air Support bombers perform ground attack missions, tearing the enemy army to shreds.

Night Flying

Night operations have a penalty to attack of -80% and a penalty of -50% on defense. This effectively makes it safer for bombers to conduct nighttime bombing runs, and it makes INT and FTR less effective in combating them during the night. Air Doctrine research gives greater advantage to the bombers, eventually with the elimination of the defense penalty entirely. This is essential for effective use of STR in particular.

Aircraft In-depth

Interceptor vs. Fighter

Interceptors are designed to defeat bombers (STR, TAC, CAS, NAV), while Fighters are designed to achieve air superiority. For this reason, fighters will defeat interceptors in an "even" fight, and will perform decently against enemy bombers. Interceptors, on the other hand, will severely punish enemy bombers, causing heavy damage and forcing enemy bombers to abort their mission.

Fighter Overview:

Superior Range (necessary in the Pacific)
High cost to build
High cost and time to repair
High supply/fuel needs
Technology comes later
Decent at non-conventional uses (ground attack, etc)
Excellent for JAP and USA due to range issues

Interceptor Overview:

+25% combat bonus when fighting bombers
Inferior Range (not needed due to defensive role)
Low cost to build
Low cost and time to repair
Low supply/fuel needs
Technology comes earlier
Very poor at non-conventional uses (ground attack, etc)
Rocket interceptors are very poor and need two more aircraft techs to be researched before interceptors can upgrade to turbojet models
Excellent for GER, USSR, ITA, UK

For these reasons, many players exclusively build Interceptors. A combined force of Fighters and Interceptors is the most potent combination possible.

Escort Fighters

Escort Fighters (ESC) are always a necessity for TAC, STR, and NAV since they significantly reduce the org and strength damage taken by bombers, which results in improved bomber effectiveness. In HOI2, NAV were extremely dominant, and did not technically need escort fighters. In HOI2 DD and ARMA, NAV must have ESC. CAS cannot have escort fighters, and as a result are more likely to receive more damage in combat. Historically, it was determined that the most effective bomber/escort ratio was 1:1, and this remains true in the game. In HOI2, escort fighters are distinct aircraft units, and thus should be grouped with bombers. In HOI2 DD and ARMA, escort fighters are aircraft "brigades", and can be directly attached to bombers.

Carrier Attack Groups (CAG) are the other type of escort fighter in the game, and function as a naval brigade. A carrier (CV) without a CAG is a carrier without any aircraft, which of course is a worthless Carrier. Naturally, all Carriers must use a CAG to be effective. As an added benefit, as technology upgrades occur in escort fighters, naval CAGs in port will automatically be upgraded. This effectively serves as a carrier upgrade, making carriers the only ships in the game that can be effectively retrofitted.

Strategic Bombers

Strategic Bombers (STR) are only truly effective with Air Superiority established for a certain region, or when flying at night. STR are very vulnerable targets and are also expensive and time consuming to repair. At the same time, STR are generally the only way to achieve air superiority over enemy territory, with the obvious exception of capturing enemy provinces. In game terms, capturing provinces is almost always easier that achieving air superiority.

When STR performs logistical strikes, enemy IC is reduced in the province. That in turn lowers the target's ability to supply, reinforce, produce, and upgrade his military. It also lowers his TC, which may lower the ESE of his troops in the field.

On a naval note, Port Strikes with Strategic aircraft have much the same effect on enemy naval forces as Runway Cratering missions do with his air forces. You don't need to sink his ships if they can't be repaired, refueled, and rearmed. As Great Britain, hitting German ports can be a major boon to keeping your supply lines open. Your convoys don't have to worry about submarines that are undersupplied and spending months longer in port to repair.

[ ]{#Tactical_&_Close_Air_Support_Bombers} Tactical & Close Air Support Bombers

Once you have established air superiority, it is time to use your Tactical and CAS aircraft to effect. Your use of air is meant for one thing, and one thing only, winning on the ground.

Ground Attack and Interdiction are your bread and butter in this case. Use a combination of these attacks for greatest efficiency. TACs are best at Interdiction and Ground Attacks are best for CAS. Technically, both are very good at both missions. The increased attack values of CAS above Basic level combines with shorter flight times and increased ground attack efficiency to make for truly staggering numbers. And once an enemy unit breaks and is on the move, Ground Attack missions from CAS aircraft will severly tear them up. Additionally, the CAS is much more effective as the war goes on and enemy Softness factors begin to drop.

Naval Bombers

Naval Bombers are highly capable in Naval Strike missions. In fact, NAV was so powerful in the original HOI2 that many players refused to build any naval ships, and instead solely built NAV! NAV could utterly decimate any fleet in the water, without taking any serious damage. As a result of this extreme imbalance, NAV were weakened in DD and ARMA, though still quite capable. In addition to Naval Strike, NAV are capable of convoy bombing. They are not as good as submarines at convoy bombing, but they are still effective in this dual role.

Naval Bombers (NAV) are fairly unique among other air units, in that air superiority is considerably less important. This is partly because there is no AA over sea zones, and ships generally have much weaker AA than land units, which is historically accurate. Also, it is far more important for nations to use their air power over their own land units, rather than patrolling sea zones. Thus, NAV are generally quite free to roam about the oceans with little interference.

AirPower Efficiency

Airpower can be extremely effective, but it is not necessarily the most efficient use of resources, which is often a focus for veteran HOI2 players. HOI2 has been modeled in such a way that *the most efficient* use of military resources is an Infantry-only army. The IC, time, supply, and repair costs associated with Infantry beat out any other type of unit by a large margin, including air units. Also, mastery of air power is challenging in terms of time, cost, and research. While many nations can find a particular, effective use of airpower, extremely few nations can manage to have a presence across the spectrum of air options.

This being true, Airpower does have specific, unique advantages:

Constancy of Attack - Air power can apply pressure and damage to an enemy continuously, while land force must advance. The ability to continue to damage the enemy and keep him on his heels when he's been knocked back can mean a difference of a lot of IC and manpower spent on reinforcement.
Wide Ranging Effect - This applies to the Strategic strategy more so than the Tactical strategy, however it is applicable to both. The wide ranging effects of damage to IC can be devastating. 8 air divisions (4 bombers with 4 escorting fighters) hitting a province like Dresden, Cologne, or Berlin with maximum ToT can translate to big TC and production losses. TC dropping down reduces ESE of ALL of his armies. When a unit hits supply problems, they start getting a -.5% combat efficiency loss for each 1% of ESE below 100%. This can be very damaging. What other investment of IC can get a combat efficiency penalty across all units in an enemy army, navy, and air force, REGARDLESS of the size of their army (you might say "easier with a bigger army")?
Speed of Response - CAS and TAC aircraft can move across a continent faster than any other unit. If the enemy is making an unexpected attack, or gaining an unexpected advantage, air power is flexible enough to move to the other front and blunt the enemy assault. An armored attack can grind to a halt under heavy attack from CAS aircraft. Sending an infantry division to reinforce a defense can take some time, especially in lower infrastructure areas (can we say Russian Steppe, or Africa). Sending in aircraft for the same purpose can take an hour or two. An hour can be all the difference in winning an losing.

Miscellaneous Tips for Using Air Power

A few other tips before I wrap it up:

Make sure to mark any air unit messages as Show Message Popup and Pause. If you do this, you won't forget the aircraft, and once one mission is complete, you can go and examine your forces, determine their readiness, and get them back up again without missing a beat.
Produce early, produce often - Air divisions are rarely destroyed (unless you let them get overrun). Produce them early and upgrade them. You can pump out infantry much faster than you can aircraft. Get your air forces up to fighting trim before you go to war.
Continue to expand your air force as you go, planning ahead for future operations. If you want to keep England out of the war while you work on Barbarossa, keep your Luftwaffe expanding so that you can maintain the pressure on a crunched England while you deal with Stalin on the East Front.
Change your focus as the need becomes apparent. If you've managed to achieve air superiority as Great Britain, when D-Day is getting closer, go ahead and start working on some CAS aircraft or increase your TAC ratio in your air force. Certainly, the CAS won't be as effective as the TAC, but they're cheap and they can make a difference on the battlefield when your enemy's advantage in technology is nullified (An ME 262 on the ground isn't going to do much against your older, slower CAS aircraft in the air).
Once You Go Up, There's No Coming Down - Realize that once you commit to air power, you're going to have to intentionally lag in one area. If you're Germany or the USSR, you won't have the resources/time for effective naval investment.
Getting aircraft where you want them - Ground Attack and Interdiction missions will be most telling in battle. The targeting AI DOES prioritize active combats as targets. However, if your air units are in the air when combat starts, they may already be targeted, or in the middle of a mission, and won't go where you need them. By the time they've returned to base and head back out again, chances are the ground combat is nearly over. Use the planning boxes to launch your aircraft one to two hours AFTER you begin a ground attack. If you win before they arrive, then the enemy will get hit on the move for big time results. If the arrive before you win, watch the little green bar shrink.
Too Much of a Good Thing? - Yes, there is too much of a good thing. Use your air power in moderation. Each division above 2 in one combat gives a -2% effectiveness to ALL aircraft in the combat. If you have 30 CAS all attacking one target, you're not going to get results. Any over your command limit (minimum of 14) are going to be fighting immediately at a -25% penalty. Then everyone is going to get a -56% penalty for all those aircraft.
Be Mindful of Mother Nature - Weather can be detrimental to all military missions, but it is the one thing other than free ranging enemy bombers that can GROUND your air forces. While not paying attention to the weather with land forces means that you can expect a harder time of things, not paying attention with aircraft means MAJOR penalties. If you have storms or blizzards in the target area, aircraft cannot attack. If you have storms or blizzards over your airfield, they can't even take off. Rain and Snow can have a detrimental effect, but you can reduce this effect by researching the appropriate doctrines for the aircraft type. Attacking at night in the rain is pointless. Ground your aircraft and save the oil.