The user interface of Hearts of Iron IV will be immediately familiar to veterans of Paradox strategy games. The left hand of the screen will be used to manage large 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 game and the world.
- 1 Top Information Bar
- 2 World tension
- 3 Main Menu Bar
- 4 National information and development
- 5 Research
- 6 Diplomacy
- 7 Trade
- 8 Constructions
- 9 Production
- 10 Recruit and deploy
- 11 Logistics
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. It is not possible to exceed 90% national unity, even if mods with additional sources of national unity are utilized.
- Political power
- This is the amount of political capital the nation's leadership has accumulated. Political power can be spent on completing national focus ideas, recruiting military and scientific advisors, changing trade and conscription laws, and some diplomatic actions. Each nation gets 2 points of political power per day, modified by certain traits, individuals, player actions or characteristics.
- 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.
- 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.
- The number of convoys or transports that are available. Each trade for strategic resources requires the allocation of a convoy unit. Moving land units across oceans and seas requires an allocation of transports. The number of available transports can be increased by building new convoys in the unit production menu.
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.
Main Menu Bar
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.
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.
- 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
Production and research
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.
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.
The gray button at the top of the screen 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.
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.
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.
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 gray button with the crane opens the construction menu. 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.
- 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.
- 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 weapons
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.
- Naval base: Assists in overseas supply limits and ship repair speed
- Land fort: Hardens the defense of units
- Coastal fort: Hardens the defense against amphibious attacks
Province buildings are built on the smallest territory size in HoI4, the province.
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.
Recruit and deploy
The gray button with the tank opens the army planner menu to recruit and deploy units. This is where it is decided what types of divisions are to be trained. These divisions will be filled by the equipment and vehicles built in the production menu. What is required to complete a new unit is shown by hovering over the green progress bars.
The country starts with a few default divisions that can be built. Army experience can be spent to design new division templates or edit ones that already exist.
The game starts with reinforcement and upgrades given equal weight with the creation of new units. If it is preferable focus the energy of new tanks or artillery on fresh units, instead of trickling equipment to the field, reinforcement priorities can be set on this screen as well.
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 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.
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.