Even though the manual for HoI2 is vastly better than it's predecessor, it does not cover all aspects of the game and the game continually changes with each new patch. This FAQ is mainly intended to complement the manual and is not meant as a substitute. I also recommend that you take a look at the HoI2 FAQ over at the HoI2 Wiki. Since it's in Wiki format you can also add/change to the FAQ all by yourself 
EDIT: With new patches out (currently 1.2) some parts of this FAQ might not be totally up to date, and I currently do not have enough time to keep this FAQ updated to each new patch. Please look at the HoI2 Wiki instead (link above).
The manual mentions that there are pdf-files on the game CD, where do I find them?
Actually there are no pdf-files on the game CD. Let's hope Paradox provides us with these along with a future patch.
How do I build Tiger tank divisions?
In HoI2 you can not build entire divisions of heavy tanks (Tiger, Königstiger, etc) or super heavy tanks (Maus etc) like you could in HoI1. You can only build light and medium tank divisions. Heavy and super heavy tanks instead exist as brigades that can be attached to your divisions. Heavy tank brigades can only be attached to armor, light armor and mechanized infantry divisions. Super heavy tank brigades can only be attached to armor and light armor divisions. No other division types, including infantry, can ever have heavy or super heavy armor brigades attached.
How do I build advanced light armor divisions?
The advanced light armor is represented as a brigade, just like the heavy and super heavy tanks. In other words, your improved light armor divisions (light armor, model III) will NOT upgrade into advanced light armor, it will instead upgrade into ordinary armor (basic armor, model III). The effects of the light armor brigade are similar to those of the armored car brigade.
All these different types of tanks confuse me, how does it REALY work?
In HoI2 tanks are represented in two different ways: as seperate divisions and as brigades which can be attached to divisions.
Tank divisions: There are two different types of tank divisions, the light armor division and the armor division. For each type of division there are various models (I, II, III, IV etc). The light armor division has three different models (I to III) and the armor division has six models (I to VI). When tank divisions upgrade they will always be upgraded to the next model number (I -> II, II -> III etc). The most advanced light armor division (improved light armor, model III) will upgrade into "ordinary" armor division (basic armor, model III).
Tank brigades: There are also three different types of tank brigades in the game: light armor, heavy armor and super heavy armor. These brigade types can never be upgraded, in other words the heavy armor brigade can NOT be upgraded into a super heavy armor brigade.
How does oil conversion work?
Energy can be converted to oil, and this happens automatically if your energy stockpile is at least twice as big as your oil stockpile. There is no way to prevent the conversion from taking place, in other words you cant turn it off even if you want to. The amount of oil you get from conversion is 10% of your effective IC. The amount of energy used is then calculated depending on your conversion tech level. In other words, getting better oil conversion tech will NOT give you more oil per day, it will simply save a bit of energy. The conversion process is NOT affected by your actual consumption of oil.
Example: Your effective IC is 200, the conversion tech is 0.25, your oil stockpile is 10,000 and your energy stockpile is 25,000. Because of the ratio of your stockpiles the conversion will be active, and generate 20 oil (200 x 0.1) each day at a cost of 80 energy (20 / 0.25). You will keep converting until your oil stockpile is at least half the size of your energy stockpile.
How does the gearing bonus work?
The gearing bonuses is an automatic bonus you recieve when doing serial production runs on units. It does NOT work on province improvements such as factories. Gearing gives you a 5% discount to the build time for each unit produced after the first one. The default cap is set at 35% discount, which can be modified by domestic policy slider settings. The biggest bonus is recieved if you have a fully planned economy, which gives an additional 10% discount, for a total of 45% discount. Any changes in slider settings will NOT have effect on existing production runs.
Example:
A unit takes 100 days to produce and you start a serial build of 20 such units. The first unit will take 100 days, the 2nd 95 days, the 3rd 90 days etc, up until the 8th unit which will take 65 days (=35% discount). All units after the 8th will take 65 days.
How does unit upgrading work?
Upgrading will take place automatically once you research a newer model of a unit and allocate enough IC to the upgrades slider in the production menu. The cost to upgrade is 1/2 and the time 1/4 compared to building a new unit of the same type you are upgrading to. In other words the total cost is 1/8 or 12.5%. This cost is affected by slider settings. It's impossible to not upgrade a specific unit (other than setting the upgrades slider to 0). You can not upgrade one unit type into another (example: you can not upgrade infantry into mechanized infantry). The only exception is light armor divivisions, if you have the final model (improved light tank, model III) it will upgrade into an ordinary armor division (basic medium tank, model III). As always this takes place automatically and you can not prevent it. Brigades upgrade the same way as other units. Naval units can not be upgraded, you must instead build new ships. You can not "skip" a model when upgrading, for example you can not upgrade 1918 infantry directly to 1939 infantry, it is first upgraded to the 1936 model.
Why am I getting Great War Manifestation as Germany in the 1936 scenario?
This event will appear randomly until you trigger the reoccupation of Rhineland event. To do this simply move one of your armies to the Cologne (Köln) province, and you will not get any more manifestations.
How do I move my garrison units?
The only way to move a garrison unit between two different land provinces is to strategically redeploy it. Select the garrison unit and right click on the province you wish to move it to, then select strategic redeploy. Garrisons can still be loaded on/off ships just like any other land division.
How do I get rare materials as Germany?
Try to trade for this on the world market before you start the war. Some nations worth trading with are the Soviets, USA and the Netherlands. Trade away your surplus energy and money, and consider producing extra supplies that you can trade away. Another way to get rare materials is to capture enemy capitals, which will give you part of their stockpile.
What is the difference between artillery and rocket artillery brigades?
Rocket artillery is cheaper and faster to produce, but gives somewhat lower bonus to soft attack and defence, plus it uses more supplies.
What's the difference between anti-tank and tank destroyer brigades?
Simply put: tank destroyers are better for offensive operations. Both have the same hard attack and defence values, but tank destoyer brigades give a bonus to toughness and reduce softness. They also do not decrease the movement speed of the division they are attached to. The bad part is they cost more IC and take longer to produce (total cost around 60% more) and they use more supplies and fuel as well. Armor divisions can not have anti-tank brigades attached.
What's the difference between artillery and self-propelled artillery brigades?
Simply put: self-propelled artillery is better for offensive operations. Both have basically the same hard attack, soft attack and defence bonus, but self-propelled artillery gives a bonus to toughness and reduces softness. They also do not decrease the movement speed. The bad part is they cost more IC and take longer to produce (total cost around 40% more) and they use more supplies and fuel as well. Mechanized and armor divisions can not have artillery brigades attached.
How much IC do I get from occupied/annexed provinces?
From both occupied and annexed provinces you get 20% of the base IC. In other words you do not get any more IC even if you annex (this was the case in HoI1). The reason to annex are others (less partisan activity, less TC drain). The only way to increase the amount of IC you get from occupied/annexed provinces is through ministers. The Prince of Terror trait on your minister of security gives you 15% more, for a total of 35% or almost twice as much.
EDIT: With new patches out (currently 1.2) some parts of this FAQ might not be totally up to date, and I currently do not have enough time to keep this FAQ updated to each new patch. Please look at the HoI2 Wiki instead (link above).
The manual mentions that there are pdf-files on the game CD, where do I find them?
Actually there are no pdf-files on the game CD. Let's hope Paradox provides us with these along with a future patch.
How do I build Tiger tank divisions?
In HoI2 you can not build entire divisions of heavy tanks (Tiger, Königstiger, etc) or super heavy tanks (Maus etc) like you could in HoI1. You can only build light and medium tank divisions. Heavy and super heavy tanks instead exist as brigades that can be attached to your divisions. Heavy tank brigades can only be attached to armor, light armor and mechanized infantry divisions. Super heavy tank brigades can only be attached to armor and light armor divisions. No other division types, including infantry, can ever have heavy or super heavy armor brigades attached.
How do I build advanced light armor divisions?
The advanced light armor is represented as a brigade, just like the heavy and super heavy tanks. In other words, your improved light armor divisions (light armor, model III) will NOT upgrade into advanced light armor, it will instead upgrade into ordinary armor (basic armor, model III). The effects of the light armor brigade are similar to those of the armored car brigade.
All these different types of tanks confuse me, how does it REALY work?
In HoI2 tanks are represented in two different ways: as seperate divisions and as brigades which can be attached to divisions.
Tank divisions: There are two different types of tank divisions, the light armor division and the armor division. For each type of division there are various models (I, II, III, IV etc). The light armor division has three different models (I to III) and the armor division has six models (I to VI). When tank divisions upgrade they will always be upgraded to the next model number (I -> II, II -> III etc). The most advanced light armor division (improved light armor, model III) will upgrade into "ordinary" armor division (basic armor, model III).
Tank brigades: There are also three different types of tank brigades in the game: light armor, heavy armor and super heavy armor. These brigade types can never be upgraded, in other words the heavy armor brigade can NOT be upgraded into a super heavy armor brigade.
How does oil conversion work?
Energy can be converted to oil, and this happens automatically if your energy stockpile is at least twice as big as your oil stockpile. There is no way to prevent the conversion from taking place, in other words you cant turn it off even if you want to. The amount of oil you get from conversion is 10% of your effective IC. The amount of energy used is then calculated depending on your conversion tech level. In other words, getting better oil conversion tech will NOT give you more oil per day, it will simply save a bit of energy. The conversion process is NOT affected by your actual consumption of oil.
Example: Your effective IC is 200, the conversion tech is 0.25, your oil stockpile is 10,000 and your energy stockpile is 25,000. Because of the ratio of your stockpiles the conversion will be active, and generate 20 oil (200 x 0.1) each day at a cost of 80 energy (20 / 0.25). You will keep converting until your oil stockpile is at least half the size of your energy stockpile.
How does the gearing bonus work?
The gearing bonuses is an automatic bonus you recieve when doing serial production runs on units. It does NOT work on province improvements such as factories. Gearing gives you a 5% discount to the build time for each unit produced after the first one. The default cap is set at 35% discount, which can be modified by domestic policy slider settings. The biggest bonus is recieved if you have a fully planned economy, which gives an additional 10% discount, for a total of 45% discount. Any changes in slider settings will NOT have effect on existing production runs.
Example:
A unit takes 100 days to produce and you start a serial build of 20 such units. The first unit will take 100 days, the 2nd 95 days, the 3rd 90 days etc, up until the 8th unit which will take 65 days (=35% discount). All units after the 8th will take 65 days.
How does unit upgrading work?
Upgrading will take place automatically once you research a newer model of a unit and allocate enough IC to the upgrades slider in the production menu. The cost to upgrade is 1/2 and the time 1/4 compared to building a new unit of the same type you are upgrading to. In other words the total cost is 1/8 or 12.5%. This cost is affected by slider settings. It's impossible to not upgrade a specific unit (other than setting the upgrades slider to 0). You can not upgrade one unit type into another (example: you can not upgrade infantry into mechanized infantry). The only exception is light armor divivisions, if you have the final model (improved light tank, model III) it will upgrade into an ordinary armor division (basic medium tank, model III). As always this takes place automatically and you can not prevent it. Brigades upgrade the same way as other units. Naval units can not be upgraded, you must instead build new ships. You can not "skip" a model when upgrading, for example you can not upgrade 1918 infantry directly to 1939 infantry, it is first upgraded to the 1936 model.
Why am I getting Great War Manifestation as Germany in the 1936 scenario?
This event will appear randomly until you trigger the reoccupation of Rhineland event. To do this simply move one of your armies to the Cologne (Köln) province, and you will not get any more manifestations.
How do I move my garrison units?
The only way to move a garrison unit between two different land provinces is to strategically redeploy it. Select the garrison unit and right click on the province you wish to move it to, then select strategic redeploy. Garrisons can still be loaded on/off ships just like any other land division.
How do I get rare materials as Germany?
Try to trade for this on the world market before you start the war. Some nations worth trading with are the Soviets, USA and the Netherlands. Trade away your surplus energy and money, and consider producing extra supplies that you can trade away. Another way to get rare materials is to capture enemy capitals, which will give you part of their stockpile.
What is the difference between artillery and rocket artillery brigades?
Rocket artillery is cheaper and faster to produce, but gives somewhat lower bonus to soft attack and defence, plus it uses more supplies.
What's the difference between anti-tank and tank destroyer brigades?
Simply put: tank destroyers are better for offensive operations. Both have the same hard attack and defence values, but tank destoyer brigades give a bonus to toughness and reduce softness. They also do not decrease the movement speed of the division they are attached to. The bad part is they cost more IC and take longer to produce (total cost around 60% more) and they use more supplies and fuel as well. Armor divisions can not have anti-tank brigades attached.
What's the difference between artillery and self-propelled artillery brigades?
Simply put: self-propelled artillery is better for offensive operations. Both have basically the same hard attack, soft attack and defence bonus, but self-propelled artillery gives a bonus to toughness and reduces softness. They also do not decrease the movement speed. The bad part is they cost more IC and take longer to produce (total cost around 40% more) and they use more supplies and fuel as well. Mechanized and armor divisions can not have artillery brigades attached.
How much IC do I get from occupied/annexed provinces?
From both occupied and annexed provinces you get 20% of the base IC. In other words you do not get any more IC even if you annex (this was the case in HoI1). The reason to annex are others (less partisan activity, less TC drain). The only way to increase the amount of IC you get from occupied/annexed provinces is through ministers. The Prince of Terror trait on your minister of security gives you 15% more, for a total of 35% or almost twice as much.
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