Player's Guide For Hearts Of Iron IV

A guide for Hearts Of Iron: IV teaching you the basics,fundementals, and advance aspects of the game

Side Note

This guide may be outdated in some parts. Keep in mind while reading.

Starting The Game

Single player offers the one-player game of Hearts of Iron IV. All other countries will be controlled by the computer. The Single Player menu allows for playing the Tutorial or to start a new game as well as to load a previous saved game.

Playing the Tutorial gives a quick run-down of the game and is therefore highly recommended. The Tutorial game may be continued as if it was a standard playthrough after finishing it.

Multiplayer enables Hearts of Iron IV players to play online with other people. Up to 32 players may play in one game of Hearts of Iron IV at the same time. The host of the game is able to start a fresh game or load a previous session that was not completed.


Options Tab
Options allows for the customization of sound, appearance and gameplay details of Hearts of Iron IV. This includes adjustment of monitor resolution and user preferences for graphics and sound. The first tab includes very important "game settings."

Once through basic setup, the player may choose a scenario and a nation to play for the duration of that play session.


Choosing a scenario
Hearts of Iron IV offers two starting scenarios - 1936 and 1939. Each presents different challenges, so the scenario chosen largely dictates the kind of gameplay the players face from the opening.
The world in 1936
The 1936 scenario begins on January 1, 1936. The 1936 scenario is the one most likely to lead to alternate versions of World War II, since it starts with fewer alliances or wars to start. 1936 is the place to begin in order to play through the organization and planning of an economy before the war starts. This scenario is about laying the groundwork for the armed forces and war plans, opening with a focus on production, research and diplomacy.

The world in 1939
The 1939 scenario begins on August 14, 1939. The Flag of German Reich has consolidated its power in central Europe and is primed to attack Flag of Poland. For a game about World War II that will be more likely (but not certain) to evolve as the real war did, it is advised to start here. This scenario is more about building, supplying and leading land, sea and air forces.


Choosing a nation
Each scenario displays a menu with the seven major powers (Flag of France, the Flag of United States, the Flag of United, the Flag of German Reich, Flag of Italy, Flag of Japan, and the Flag of Soviet Union) to choose from as well as an option to pick other countries. No matter which is selected, a map of the world is then displayed to allow for change in the choice. The player may select whatever country they wish, but one should be aware that countries like Flag of Bhutan may not be best suited as first nation to play as. We recommend any nation you believe you know the most about, or what will be the most fun!

Game settings

In the lower right corner of the map before starting the game are the game settings. Here the player can toggle ironman and historical focus on or off and use the difficulty settings to make the game harder or easier for the player and also boost the relative power of one or more of the larger nations (this makes them stronger, but not smarter). There is also an icon for showing if steam achievements can be earned in the game or not, they require ironman mode and regular or higher difficulty. When finished press the play button in the lower right hand corner to start the game.

General difficulty settings: The general Difficulty settings affect only the player. These do not give the AI any special bonuses or penalties.

The interface

The user interface of Hearts of Iron IV will be immediately familiar to veterans of Paradox games. The left hand of the screen will be used to manage national issues, alert tabs will appear at the top of the screen as a warning of things that need attention, and the right hand side of the screen will be devoted to information about troops. The very top border of the screen will include important summary information about the state of the world.

Top Information Bar
Across the top left to center of the main play screen, there is a row of numbers running from left to right.
National Unity
The measure of a nation's war-resolve. A country with low national unity will surrender more quickly than one with high National Unity. National Unity is determined by National Spirit traits that can be assigned to certain countries (France, for example, starts with very low NU), but it can be modified through National Focus choices or recruiting government officials to modify it.

Political Power
This is the amount of political power the nation's leadership has earned. Political power can be spent on completing national focus ideas, recruiting military and scientific advisors, changing trade and conscription laws, and some diplomatic actions. On average, each nation gets 2 points of political power per day, modified by certain traits, individuals, player actions or characteristics.

Manpower
The number of men available to create and reinforce military units. This is affected by a number of factors, primarily mobilization laws and the number of units under construction. In order to increase your manpower, you must change your Conscription Law.


Factories
Three separate numbers, listing the military factories, naval dockyards and civilian factories available for new orders. We will deal with their roles in a future section.

Army, Navy and Air experience
As units fight or, in the case of armies, exercise, they will gain experience. Army experience can be spent in the unit designer to edit or invent land divisions. Naval and air experience can be spent on modifications for ships and planes, giving them bonuses to speed, firepower, and so on.


Q: GOVERNMENT
W: RESEARCH
E: DIPLOMACY
R: TRADE
T: CONSTRUCTION
Y: PRODUCTION
U: ARMY PLANNER
I: LOGISTICS

The Flag and 7 grey buttons just underneath the top bar provide direct access to the primary menus that are used to interact with the country. The hotkeys for these menu buttons are noted above. They follow, from left to right, across the top row of the keyboard. The windows they open are detailed below.

National information and development

To the far left of the screen the player nation's flag is shown. Click this flag to open a view of national status. This view shows a portrait of the nation's leader, political support and parties, some active variables and factors for the nation, and three rows of items that political power can be spent on.
(You can open this tab by clicking your flag)
There will be a prompt to choose a national focus for the country. It takes 70 days to complete a national focus, and it costs one political power point per day. National Focuses are similar to research tech trees in other games, except they are connected with choices the country is making about its direction. It may choose to, for the moment, focus on industrial growth, or, in the case of Germany in most games, push for expanding its borders at the expense of its neighbors. Some National Focus choices are mutually exclusive; the Soviet Union cannot be friends with both China and Japan. From this menu, it is also possible to spend political power on changing government laws or hiring political, military and industrial advisors. Most changes will cost a minimum of 150 political power, very powerful advisors may cost up to 250.

National Focus tree of Italy, as an example


Laws & Government

Conscription law: affects how much manpower is available to the country
Trade law: affects research speed, factory and construction speed and how many resources are available to be traded
Economy law: affects how many factories are dedicated to consumer goods, manpower availability, and military production
There will also be space for three political advisors that can be hired to give the country bonuses


(Political Advisor Screen)

Research & Production
There are multiple things that can be added, such as a tank designer, ship designer, aircraft designer and material designer to earn bonuses to either production of the relevant weapon system, or affect its combat abilities.
It is possible to add an industrial concern or a theorist to improve certain types of research.

Military Staff
It is possible to add a Chief of Army, Chief of Navy and Chief of Air Force to improve research or combat skills in the relevant field. Up to three other members of the high command may be hired.

World Tension

To the upper right of the screen there is a glowing circle with a percentage below it, indicating the world tension. This percentage is the measure of how much tension is in the world. Some diplomatic and military actions, especially for democratic or neutral nations, require the world tension to reach a specific level. World tension is increase by historic events, declarations of war, and other hostile diplomatic actions.

Impacts on World Tension


Increase in World Tension
The following can increase the level of World Tension:
+Declaring war
+Taking Land in a peace conference
+Sending volunteers
+Joining a faction (in some cases)
+Justifying a Wargoal

Decrease in World Tension
The following can cause a decrease in World Tension:
+Decay over time
+Declaring war (for Democracy)
+Guaraneeing independence to a nation (for Democracy)
+Joining a faction (in some cases)
+Peace treaties

Peace Treaties
While Peace treaties can cause decrease in world tension, if the country gets annexed, it is more probable to cause an increase in world tension rather than a decrease. We will get to the peace treaties in following sections.

Ideological Effects & Tension Requirements
Different ideologies have different effects on World Tension, both in terms of generation and in terms of how much World Tension is needed to take certain actions.

Tension Required
Some national focus can lower the threshold. Below you find the base threshold without any modifiers.

Communism

World Tension threshold:

Comintern impact on tension threshold: -50%
Communist countries are not limited by World Tension.


Democracy

Democracies cannot justify wargoals against other democracies.

Democracies have the most restrictive tension thresholds:

Allies impact on tension thresholds: −10%
Guarantee independence: 25% world tension needed
Send volunteers: 50% world tension needed
Join faction: 80% world tension needed
Declare war: 100% world tension needed
Send Lend-Lease: 50% world tension needed

Fascism

Fascist countries are not limited by World Tension.



Non-Aligned

World Tension threshold:

Neutral faction impact on tension threshold: +10%
Guarantee independence: 40% world tension needed
Send volunteers: 40% world tension needed
Join faction: 40% world tension needed
Justify war goal: 50% world tension needed
Declare war: 25% world tension needed
Send Lend-Lease: 40% world tension needed

Research, Diplomacy, Trade

Research
The gray button at the top of the screen (See the interface tab for more information) marked with a beaker opens the research menu. There will be two to four slots available to research particular technologies, but pursuing specific national focus ideas may unlock additional research slots.

There are eleven categories of research. Each nation starts with an historically appropriate level of technology and theory, depending on the scenario.

All the research trees (except for doctrines) are marked along an historical timeline. Researching a technology or unit before the historic date will take longer than it would if they are researched it at or after the historic date. This penalty may be modified by pursuing certain National Focus ideas.

Infantry: researching better infantry weapons and different types of infantry divisions. This is where mechanized infantry, paratroopers, marines, mountain troops and so on will be unlocked.

Support: researching support battalions that can attach to divisions. This is where engineers, field hospitals, mechanics, and so on can be found.

Tanks: research light, medium and heavy tanks, as well as variant tanks based on the chassis unlocked.

Artillery: researching artillery, anti-tank and anti-aircraft weapons.

Land doctrine: Most of the great powers will start with an initial land doctrine. It is possible to change this, but all land doctrine paths are mutually exclusive. The land doctrine chosen will assign major land combat bonuses. (Infantry Technology Screen on the right)
Naval: researching more advanced warships, submarines and convoy/landing craft.
Naval doctrine: Some of the great powers will start with an initial naval doctrine. This may be changed, but all naval doctrine paths are mutually exclusive. The naval doctrine chosen will assign major naval combat bonuses.

Aircraft: researching different types of fighters, attack planes and bombers as well as carrier borne variants.

Air doctrine: Some of the great powers will start with an initial air doctrine. This too may be changed, but all air doctrine paths are mutually exclusive. The air doctrine chosen will assign major air combat bonuses.

Engineering: researching electrical engineering for radars (for detection) and computers (for research and encryption bonuses), as well as researching nuclear and rocket technology

Industry: researching means to improve the efficiency, productivity and resource extraction capabilities of the country.



Diplomacy
The gray button with a hand ready to be shaken opens the diplomacy menu. Here is a list of nations and a number of filter buttons to narrow down the list.
After clicking on a nation to interact with, there will be a portrait of its leader, and a little bit of information about what the nation is up to. In the upper right corner of the menu, there will be a couple of tiny flags with arrows indicating the relationship between the two nations.
There are a number of actions that can be taken in the diplomatic menu, provided the requirements are met. Democracies are especially limited in their abilities to undertake aggressive diplomatic actions unless the world tension meter has climbed to a high enough level.

Hover the mouse over each option for a description of the diplomatic action and what conditions must be met.


Additional Information

Military Access: You don't need to give another country access to your own territory if both you and the second country are at war with a common enemy. For example, if the USA, UK and Soviet Union are all at war with Germany, then the Soviet Union will have access to UK and US territory to attack/defend against Germany while the UK and USA will have access to any territory controlled by the Soviet Union. This automatically happens when warring nations gain common enemies and cannot be prevented in any way.


Guarantee independence: The Political power political power cost will start at 25Political Power for the first guarantee and will then increase by 25 for every subsequent guarantee, in the following fashion: 50 Political Power for the second, 75 Political Power for the third, 100 Political Power for the fourth and so on.

Join faction and Create faction: the conditions to cancel these diplomatic actions are essentially the same. They're the conditions to activate the Leave faction diplomatic action, except that you cannot be the faction leader when you join a faction. The tooltip does not warn you, but if you go to war along with the faction then you may not leave it, so Leave Faction is timely in the event of a Call to Arms.

Start Lend Lease: the amount of production that can be sent to the target country can be a fixed number of units out of the monthly production or a percentage of the monthly production, but not both at the same time. It's possible to modify the Lend lease at will. For further discussion of Lend Lease, refer to the Equipment section.

Stage a Coup: This diplomatic action also requires to select the State of origin of the civil war. At the onset of the civil war, the rebelling State will be joined by a number of other States, the amount of states the join the rebellion will wary based on the proportional party popularity when the full political power Political power.png requirement is filled. For this reason, Stage a Coup is more effective when combined with "Boost party popularity" to well over 50%. The amount of infantry equipment required appears to be a function of the target country's civilian population. The more populous the country, the more infantry equipment a nation has to give in preparation for the civil war. Coups will automatically succeed with over 40% party popularity if performed in a country with only one state. Otherwise a successful coup will start a civil war. For further infomation about civil wars, refer to the Civil War article.

Trade
The gray button with box and curved exchange arrows opens the trade menu. There will be a number of tabs and columns listing the major resources available, what is required and possible trading partners.
There are six major resources in the game: oil, rubber, aluminum, steel, chromium and tungsten. These are used to help in the construction tanks, battleships, planes and so forth. Each new production line of a major weapon system will require a certain amount of resources. Though it is possible to build these units without the necessary resources, production will be much slower and less efficient.
Resources are found in certain locations on the map and are not evenly distributed. Almost always it will be necessary to trade for what is needed.
To trade for a resource, click on the name of the country and move the slider to determine how much is being trading for. Resources are traded in units of 4. Each trade, unless conducted over land, requires a minimum of 2 convoy vessels plus 1 for every additional 4 units of resource.

Every eight units of a resource imported will also cost a civilian factory, with that productive power going to the nation that is being trading with. So, exports will make the country's industry stronger as factory power is pulled from other nations, but a lot of imports will make the country weaker. But it will be necessary to import resources to keep the war machine going.

The one on the left is the old trade tab, the one on the right is the new trade tab.

Constructions and Production

Constructions

The gray button with the crane opens the construction menu. (See the interface tab for more information) This is where tasks will be assigned to the civilian factories - building infrastructure, new factories, defenses, and so on.

Civilian factories make all the improvements to a territory. The number factories available for construction will depend on the size of the nation, how many factories are being dedicated to providing consumer goods for the country (the Economy Law), and how many factories that are “traded” for strategic resources. The number of civilian factories can be increased by building more, but be careful since each province can only support a certain number of factories. A maximum of fifteen factories will be devoted to a construction project, and any left over will work on the next item in the queue.

There are three categories of structure that can be built with civilian factories:


State structures
Shared structures
Province buildings







State Structures:
Infrastructure: Each state has an infrastructure rating that determines how easy it is to supply units in the state and how quickly military units can move through.

Air Base: The larger the air base, the more planes it can effectively field. Air bases house military aircraft.

Anti-air: Defends a state from enemy aircraft, and especially useful to protect industrial areas.

Radar station: Help the airforce detect and intercept enemy air fleets.

Shared Structures:

Military Factory: Used to produce weapons, equipment and vehicles.

Civilian Factory: Used to produce and improve a nation's military/industrial capacity.

Synthetic refinery: Produce synthetic oil and rubber, especially useful to nations that lack either.

Naval dockyard: Used to produce ships and convoys. Can only be built in coastal states.

Rocket site: Locations from which to launch rocket attacks on nearby nations

Nuclear reactor: Produces nuclear nukes

The number of shared structures that can be built is limited by the number of slots available in that State. The number of slots can be increased by researching Industry technologies.

Province Buildings
Naval base: Assists in overseas supply limits and ship repair speed.

Land fort: Improves the defense of units.

Hardens the defense against coastal attacks.

Production

The gray button with the wrench opens the production menu. This is where military factories and dockyards are assigned to build equipment, army vehicles, ships and aircraft.

The more factories dedicated to building a specific item, the more will be produced. Infantry, armor and artillery units made will then be assigned to the appropriate military divisions, either for new units being constructed or reinforcement and upgrades for units in the field. Airplanes produced will be deposited into a reserve pool. Naval units will be automatically placed in a port, though they can be assigned to a specific one if needed.

Factory output is dependent on the availability of strategic resources for higher end units, and on the efficiency cap of the nation's industry. New production lines will take time to be perfectly efficient, and if factories are added to a production line, some efficiency will be lost. Factory productivity and efficiency can be raised in the Industrial research tree.

Logistics

Logistics
The gray button with the paper and pen opens the logistics menu. This menu gives an overall summary of stockpiled equipment, whatever shortages the country might have, as well as a rundown of how many strategic resources the country is missing from the production lines.
The logistic screen provides the general overview of the nation's equipment and resource situation. The center of the screen consists of the equipment, and only shows equipment that is being produced, stockpiled, or used in the nation. In addition, the equipment will have a green hue to the background if it is land equipment, white if it is air, or blue if it is sea. The following provides a description of all of the various parts of the screen.

Average production efficiency, which has a Production efficiency.png above the column, shows the average production efficiency of all the lines of production producing that type of equipment. The yellow bar inside the area represents the average production efficiency.
Equipment type, which says 'Equipment Type' above the column, provides the name and a picture of the equipment that is either being produced, stockpiled, or used in the nation.
Amount produced, which has a wrench being held by a hand above the column, shows how much of that particular equipment is being produced per day.
Status is the green bar next to the amount produced showing how much of the equipment need is being produced. There is also a slider button that lays on the left if the nation is running a surplus of that equipment each day, and on the right if the nation is running a deficit of that equipment each day.
Need, with a hand at the top of the column, is how much of that equipment the nation needs each day.
Balance is the surplus or deficit being ran each day by the country, represented by a scale at the top of the column. If the nation is running a surplus, it will say +Amount, but if it is running a deficit, -Amount.
Stored is the stockpile of the nation. It will be in green with the stockpiled amount if the nation has extra of that equipment, and will show red with the amount missing from the nation, such as the amount needed to reinforce, equip new units, or, for convoys, how much is needed for current trade.
Resources shows the resources that the production line is currently using to produce that equipment. If none of that equipment is being produced, it will not show the resources.
The bottom of the screen includes extra information.

Military factories has a green bar indicating the percentage of the nation's military factories that are currently in use.
Naval dockyards, like military factories to the left of it, shows the percentage of the country's naval dockyards that are in use.
The six icons to the right hand corner show oil, rubber, steel, aluminum, tungsten, and chromium. Next to each icon will be either a green number showing the nation's surplus of that resource, or a red negative number showing that nation's deficit of the resource.

Stockpile Screen The stockpile screen is accessed by clicking on any of the equipment on the logistics screen. The graph in the center of the screen shows the change in the stockpile over the previous 30 days, 12 months, or 7 years, each of which have a corresponding button above the graph. The change is represent by a red line, and the X-axis of the graph is the time variable, while the Y-axis is the stockpile variable. Below that is a mini overview of the equipment, which shows the variants of that equipment (i.e. Basic Infantry Equipment vs. Weapons I) and the amount stored of each variant and weekly production of each variant.

Recruit & Deploy

The gray button with the tank opens the army planner menu to recruit and deploy units. This is where you decide what types of divisions you want to train. These divisions will be filled by the equipment and vehicles built in the production menu. You can see what is required to complete a new unit by hovering over the green progress bars. You start with a few default divisions you can build. You can spend army experience to design a new division template or edit ones that already exist.

The game starts with reinforcement and upgrades given equal weight with the creation of new units. If you would rather focus production of new tanks or artillery on fresh units, instead of trickling equipment to the field, it is possible to set reinforcement priorities on this menu as well.

Training
Training allows a unit to start with experience, increasing its capability in combat. The maximum amount of training may be affected by conscription laws.

A unit cannot be trained faster than it is equipped and only to the experience level of trained. Deployed troops may usually be trained by military exercises up to regular level, which provides greater combat effectiveness, while further experience must be gained in combat.

Equipping
Equipping occurs instantly, limited only by the country's inventory of equipment on hand. Once a unit has at least 20% training level it may be deployed onto the map using the planner. However, this comes at the cost of less starting experience which gives a hefty Green/Fresh -25% modifier in combat.

Lend Lease
Lend-Lease is basically a donation of equipment to another country. See the discussion of Lend Lease under Lend Lease and the Lend Lease diplomatic options under Diplomacy. The Army Planner first displays a separate panel with tooltip information for each of the player nation’s Lend Lease relationships. Any changes or cancellation must be made through a diplomatic action. (See diplomacy part for more information)

Reinforecements and Upgrades
Reinforcements are replacement of the lost equipment of existing units. Upgrades are replacement of their existing equipment with better equipment. Troops will seek higher tier equipment if made available to them.

It is also possible through the division template to downgrade equipment for a division template (e.g., giving a garrison or security division old small arms) to free up better equipment in the future for more important uses or assign old equipment to be used up in training and military exercises.

The Reinforcements and Upgrades panels offer tooltip information on current equipment requests and the ability to set high, medium, or low priority that determines how equipment as a whole will be allocated among competing needs for reinforcements, upgrades, and equipment of recruits for training. These decisions have important effects down the road.

Set up a Training command: Create a new army ordered to exercise (it may also be ordered to Garrison Area so as to serve a useful purpose) and assign to it all freshly deployed units. They will increase their experience to regular level, after which they can be switched to a front-line unit or continue exercise to create a small flow of added land experience at the cost of consuming further equipment. Using the fortress tower icon and the color green for a garrison army training green troops was a Let's Play idea that may be easy to remember.

Controlling the army

The player can move their units by selecting them with the left mouse button and then clicking their destination with the right mouse button. If one draws a box around a group of units using left click and drag, all units inside the box can be commanded. One can move troops across the ocean to friendly territory, by sending the units to a province with a naval port and then shift-clicking on a destination port. For an overview of all divisions, including indications of their combat status, click on the Army View icon under the date or press hotkey "o". Right-click on a division's info bar to pan over to it or hold down shift and left click on multiple units to select them all.

Troops are more effective when they are grouped into armies under a commander's command and given plans to execute.

Creating command groups/armies
The player can create armies of units by selecting a group of them and then clicking on the silhouetted portrait or green plus sign that one will see at the bottom of the screen. Then, go to the selected unit profile in the upper left and click on the silhouetted portrait. This will open up the list of generals to be assigned to armies. There are two types of military leaders – generals (who can effectively command a maximum of 24 units) and field marshals (who have no limit on the number of units they can effectively command). Commanders may also have attributes that give them bonuses in certain types of combat situations. If one promotes a general to field marshal, they lose their attributes (except "old guard") as field marshals have different attributes.

Experience and giving orders
Countries will gain army experience mostly through combat, but one can start a trickle of early experience by having soldiers "exercise". To do this, select the army group and, in the unit profile in the upper left of the screen, click the exercise button in the upper right of the menu. Be aware that this results in higher equipment attrition, which may not be desirable as a country with limited industrial capacity.
One can spend experience to promote generals and allowing them to lead more troops, or to create and edit new division types in the unit production menu.

An army group can be commanded like any other group of units and simply giving a right-click move order to a destination. However, they will fight better if they are given "battle plans" – a general order that is coordinated along a front, either to advance or defend.

When the player selects an army group, they will see a row of general orders appear at the bottom of their screen. Each of these has rollover text that explains in detail how to use this instruction. This guide will focus on the most important ones.

Naval invasion: Use this for amphibious attacks on enemy territory. (One can move into friendly territory this way, but it is more efficient to simply use port to port movement as described above.)

When one selects naval invasion, one will be asked to left-click on an origin point. This is where the army will gather for the assault. Right click on the enemy province one wants to invade. Note that one will need to have some naval intelligence of every sea lane they will be crossing, so one will have to have warships patrolling or hold naval superiority in those sea areas.

All plans take time, and amphibious invasions take a lot of time to plan. Once the weeks (or months) of preparation are ready, the grey arrow above the army group will turn a faded green. Press that arrow to activate the plan.

Land operations: To make a battle plan for offensive land operations, one must first define one's defensive front – this is the point from which the army group will begin their operations. Select the defensive front button and, on the map, draw a line to indicate where an army group will start. (In many cases, this will be a national border or the current line dividing enemy armies). Then, click the offensive front button (a line with an arrow) and draw the front to where the armies should advance.
The army group units will begin to organize themselves along their defensive front. When they are in place and one is ready to begin, press the green arrow and the units will begin to execute the plan.

One can research doctrines and hire advisors that will reduce the time for a military plan to be prepared or add bonuses to units that are operating with a plan.

Controlling the navy

Ships will be automatically grouped into fleets at ports as they are constructed. If one does not like the way fleets are organized, one can drag-and-drop silhouettes of ships from one fleet to another.
Assign commanders to one's fleets by clicking on the silhouetted portrait and choosing from available naval commanders. Political Power points may be spent to recruit new admirals for the fleets. Like generals, admirals may have skills that are assets in particular battle situations or while commanding certain types of vessels. Admirals do not have a maximum amount of ships to lead.
[/previewimg]If a fleet is selected, a row of different orders will appear above it. These range from simple patrol missions to convoy escort duty. Choose a mission for the fleet (submarines, for example, are best used to interrupt convoys), and then right-click on up to three contiguous sea zones, i.e., sea zones that touch each other. This fleet will then carry out that mission over these areas. One can remove these orders by returning the fleet to port and assigning a new mission. So long as a fleet is operating in a sea zone, enough intelligence should be gathered about that zone to both route supply overseas through that region or to order an amphibious assault across that space, but if the enemy is active in the region, naval superiority is also requiredIf a fleet is selected, a row of different orders will appear above it. These range from simple patrol missions to convoy escort duty. Choose a mission for the fleet (submarines, for example, are best used to interrupt convoys), and then right-click on up to three contiguous sea zones, i.e., sea zones that touch each other. This fleet will then carry out that mission over these areas. One can remove these orders by returning the fleet to port and assigning a new mission.

So long as a fleet is operating in a sea zone, enough intelligence should be gathered about that zone to both route supply overseas through that region or to order an amphibious assault across that space, but if the enemy is active in the region, naval superiority is also required.

Controlling the air force

Unlike other units, airplanes that are constructed are sent to a reserves hangar. One can mobilize them by clicking on an airfield, then creating a air wing using the button to the upper right of the resultant menu (it has a plus sign). The larger the airfield, the more planes it can efficiently use.

Like naval units, air units operate over regions and are given specific missions relevant to the type of aircraft. Fighters can do air superiority or interception, strategic bombers can target industry or infrastructure, tactical bombers can do close support of land attacks, and so on. To assign an air wing to a region and a mission, click on an air field. This will open the air information map mode.
Left click on an air wing and then right click on the region where it should operate. One can decide what mission it will perform. Planes have limited range depending on their type (strategic bombers have a much greater range than interceptors) and design (dependent on technology researched or experience spent to edit their abilities).

Supply

Armies in the field will require supplies to remain in fighting shape. An army out of supply can take no offensive actions at all, including simple movement, even if unopposed. Supply is determined on a territorial basis (i.e., potentially larger than a single State) where each territory is able to support a specific number of troops. However, the final value of this supply to an actual unit is modified by the infrastructure of the State the unit is stationed within. If a territory can support 10 units easily, but if the army is in a province with very low or damaged infrastructure, a supply bottleneck will develop, so not every unit in that army will get what it needs.

Supplies coming over land are also provided by adjacent territories - which forms a supply line back to the capital or an alternate territory if the capital territory is not in one's control. This is why it is particularly important to maintain and defend contiguous States between home and the front lines.
When land paths are unavailable supplies will be transported via sea. Overseas supply is done through convoys and sea ports. Larger ports can funnel more supply across the ocean, though this will also require more convoy ships. For overseas convoys to be most effective, one will need to assign some of one's naval vessels to Escort duty in the regions that they will cross.

The player can check the supply lines and capacities by clicking on the Supply map mode in the menu to the lower right of the main screen.

Tips to get started

As the player is learning Hearts of Iron IV, remember these important steps as one formulates their plans for world domination.

One will start the game with a few production lines of weapons already active. The most important of these will be one's infantry equipment, so, until more military factories have been built, put most of one's energy here.


When a country is training new units, have multiple lines of infantry going at once. If one doesn't, one will fall behind in army size.

Plan out National focuses early in the game. For instance Germany will want to move quickly along the paths that give it claims on Austria and Czechoslovakia. The USA will need to get itself out of the Great Depression. France has to watch its political stability. Have a long term goal in mind.

Keep in mind you don't have to research all the National Focuses one after another. Sometimes it is best to wait a bit for the opportune moment, especially with research boosting focuses.
Each nation has access to extra research slots if they activate specific national focuses. These are easily identified by the beaker icons on the names (though some focuses with that icon give research bonuses instead - read the tooltips for details). The sooner these are unlocked, the better the army will fight.

When researching, try not to rush too far ahead since there are significant penalties to pursuing technology too early in the timeline. However, if one researches computing in the electrical engineering track, one can reduce their total research time by a significant margin.
If a powerful navy is not central to one's war plans, one can usually ignore this aspect of the war and research tree. However, convoys are always useful for trade and supply, so have whatever dockyards owned should focus on that.

If one is at peace, armies should exercise so they can train until they reach regular status and earn experience. Adding an extra regiment, line battalion, or support company to an existing division design is an easy way to beef up one's forces – unless one doesn't have the equipment on hand to reinforce what one has.
In wartime, it is often better to let the new equipment fall into the hands of new units instead of reinforcing and upgrading old ones. Adjust the reinforcement and upgrading of troops with an eye to what one needs now – more active units in the field now or a stronger punch in a few months time.

Democracies should change their economic ideas as soon as they can in order to free up civilian factories that are otherwise dedicated to producing civilian goods.
Don't forget to rest armies after they have reached their objectives. A few days of inaction will help with organization, reinforcement and supply.

More Advanced Tips

Remember infrastructure and fortifications. Should one be attacked, a line of land forts and a battle plan for a defensive hold along a strategic line (like mountains or a river) could give the player time to hold off an invasion as he waits for help from allies and/or their own reinforcements.
If you lack a resource, but produce it locally (i.e. steel is produced, but not enough of it), try to avoid trading for it unless absolutely necessary. You can research excavation under the industry tab, which will increase the amount of your produced resources by 10% for each tier, up to 50% bonus if all tiers of excavation are researched. This will free up your civilian factories from trade and allow you to construct more buildings.
When there is a lack of material, remember to check what is being produced. It won't do to have too many different recruits going at once (i.e both motorized and infantry) if what the factories are producing is going toward upgrades. An example would be to trim away motorized infantry for a while and focus on just regular infantry. If one lowers the production of motorized and focus that on upgrading an existing unit, the free factories can be moved to infantry equipment and by extension allow for the production of more units.
When Manpower is low, remember to change your conscription law and try attaching Field Hospitals as support companies or disbanding units you don't need, including air wings and ships. If you must maintain a large front and can't afford to reduce the number of divisions you have, you can consider making them smaller. Quite often you can afford to remove one infantry battalion from your default divisions and they will perform almost the same. Keep in mind that the Total Mobilization (Economy Law) gives you -3% recruitable population and generally isn't worth having, unless you can spare the manpower. The Mobile Warfare and Mass Assault Land Doctrines, as well as the Nationalist branch of the general National Focus tech tree give bonuses to your manpower pool. If you have concerns about your manpower in the long run, consider creating high-tech divisions with advanced equipment. Higher production cost is generally linked with manpower preservation - an infantry division will lose a lot more manpower than a mechanized division. Mountaineers and Marines will save you a little bit of manpower, compared to regular infantry, if deployed properly in their respective fields, due to their combat bonuses in mountains/hills and river crossings/naval invasions, as well as their slightly higher breakthrough stat, and they only cost more Infantry Weapons and training time to produce.
Doctrines should be picked carefully and with consideration. It is possible to switch from one doctrine to another, should the need arise, but it takes a long time to research them and you will lose the old doctrine. The good part about doctrines is, that they don't require production and the bonuses come into play as soon as you research them. There are about 10 separate researches in Land Doctrines, 12 in Air, and 15 in Naval. The base cost is 300 days for Land Doctrines and 200 days for Naval and Air Doctrines, so it will take considerable time to replace a fully researched doctrine. Use caution should you decide to make drastic changes.
Remember to update and research and produce the next tier of equipment for units you find lacking in quality. Sometimes an upgraded version of a unit has a lot more hidden bonuses than one might expect.
Different Factions have different disadvantages and advantages when it comes to securing resources. The Allies begin with the majority of Rubber production, and anyone going to war with them will have serious troubles with securing rubber without a plan to attack Allied South-east Asia, or without a lot of Refineries. Rubber is needed for all aircraft, as well as motorized/motorized artillery and mechanized. The most of the world's Chromium can be found in the Soviet Union, Turkey, South Africa, France, Cuba and Yugoslavia. Chromium is needed for ships and heavy tanks, as well as modern tanks. The only ships that don't require Chromium are Destroyers I-III, Light Cruisers I-III, Heavy Cruisers I-III, Submarines I-III. If you want to maintain a fleet of capital or modern ships, you will need to secure those places for yourself, or as allies. Aluminium can be found in France, the United States, Hungary, the Soviet Union, Yugoslavia. Aluminium is needed for all aircraft, as well as support equipment. When planning your strategy you have to plan to either skip mass production of units requiring resources you don't have, or to plan to steal those resources from the enemy to secure your production or deny the enemy production of a particular equipment type. If you are playing as a minor nation, you might want to consider which side to join, if any, depending on the resources you will need to power your economy.
Naval and Air combat seem confusing at first, but with a bit of research and understanding, turn out to be simpler than Land combat. Look up an in-depth guide if you have problems with Air or Naval battles and/or strategy.

FAQ

How to produce equipment?
First start by clicking the Production icon in the top of the screen. All Equipment is produced by Production Lines. To add a new Production Line, click one of the buttons in the Production screen and select the desired Equipment to produce. When the Production Line has appeared in the list, assign more Military factories military factories or Naval dockyards naval dockyards to the Production Line. A Production Line can have up to 15 factories assigned to it.

How to build units?
Land units are queued through the Army planner. A new Division will require Equipment in order to complete its training. When a unit has all the equipment and training it needs, it will be deployed to the chosen location.

Air units are deployed as Air Wings. An Air Wings contains equipment of the same type, a Fighter Air Wing, for example. Air Wings are located in Air Bases and a new Air Wing can be created in that interface.

Naval units are deployed directly as equipment after being produced in the Production interface.

How to research new technologies?
In the Research screen to see the Research Slots available. Several technologies can be researched simultaneously because each slot can research a Technology. It is possible to unlock a new Research Slot through the country's National Focuses.

To research a Technology, click on an empty Research Slot to open the Research Tree. Once the Research tree is open, select a technology to research.

What do National Focuses do?
National Focuses are a way of making the game progress by allowing a country to set goals for itself and advance its political and strategic agenda.

They can be found by clicking on the flag at the left hand side of the screen. The National Focus tree is vital for a country's development, so study them by hovering the pointer over each focus.

There is no one single correct way to take them on. It all depends on the strategy of a country. Is war as soon as possible a goal? Is a build up of the civilian industry and military capacity a country focus? Is a naval focus the priority? The answer to all of these questions will determine the best path through the National Focus tree. There are some things Germany need: The focus “Danzig or War” is a prerequisite for war. Take notice of the prerequisite for some of the National Focuses. Several of them require a minimum number of divisions.

How to build buildings?
To construct buildings use the Construction screen. Some buildings are built in a province (Bunkers), while most buildings are constructed on a State level (factories, Anti-Air instalments etc.). Buildings are constructed by  civilian factories.

What is Political Power used for?
It can be used to activate new Ideas and to change country Laws or to take certain Diplomatic Actions.

FAQ From The Comments Section

How can I delete frontlines?
When you select your army there is Battle Plans. You can delete the frontline by clicking the one on the right called "Delete Order" and selecting the frontline.
You may consider watching this video to get in-detail about battle plans.

How can I increase manpower?
Lets start with the meaning of manpower. As seen in the "The interface" section, manpower is the men available to create and reinforce military units. This is affected by a number of factors. In order to increase your manpower, you must change your Conscription Law.

[wojtekpolska]

how do i use the tutorial? i start it and all it does is show how to use the mouse and a link to in-game wiki

[Kozmas]

thanks that guide is very usefull now I can administer my countries goverment in real life.

[Metodija]

@bottle
GET SOFT ATTACK DIVISIONS
3 artillery atleast
20 width if you really want to but 40 width is if you can afford it (like the US)
for ur tanks 40 widths are preferably with SPGs in medium tanks and tank destroyers for heavy tanks (thats my play strat)
lots of CAS and Air aswell, you need atleast 10 factories as germany on fighters and 5 on CAS

[minniefinnie]

how do you zoom in and out?

[NEO]

@connorc909 git gud

[stevedelaminecraft]

outdated guide

[GNU+Swag]

I just want to know why the French divisions have 400 defense man

[The Deaf Guy]

I am playing as Soviet Russia, and im trying to take out Poland. the best I can do is put a few dents into their defenses, but nothing decent. I have atleast double their troops, and about half my troops are decently trained, have a good organization, and supplies, yet they can only seem to get past a green 60% odds if they have overwealming odds (sometimes that doesnt even work)... can I have some suggestions? keep in mind germany is not fighting with them, and in fact sending volanteers, along with franch and all the britain controlled places.

[DukeMcGregor]

how do I look at my army's equipment and how much it has

[captgeo]

wow, great guide