Naval warfare

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The basic functional unit for naval forces in Hearts of Iron IV is the fleet. While these fleets are made up of individual ships of different classes which can be named and customized, in order to use them at all they must be assigned to fleets. It is the fleet that carries out naval missions and naval combat, and while the individual ships in those fleets can gain experience or be sunk, they are at all times assigned to a fleet and take action in the game as part of a fleet until sunk or scrapped (i.e. deleted). Each new ship produced is either automatically assigned to a designated existing fleet or to a new fleet of its own in a naval base that may also be specified by the player.

Naval combat is mostly automated through mission orders assigned to fleets and to be carried out in particular sea regions. A single fleet can cover at most three adjacent regions, combining them into one large patrol area. Orders can specify how sensitive the fleet is to damage and they will return to their home base to repair automatically when predetermined damage levels are reached (it is also possible to order damaged ships to automatically break off and return to the fleet's home port to repair while the main fleet continues its mission - once repaired, these ships will later rejoin the fleet automatically). Fleets can also be ordered to engage the enemy or to avoid combat. Admirals may be assigned to fleets to improve offensive and defensive combat abilities proportional to their skill level and provide the benefits and bonuses of any individual traits they may have.

Navy Overview[edit]

Navy Overview screen.

The Navy Overview can be opened by pressing the P hotkey or clicking on the Navy Overview.png Navy icon in the top right corner of the screen. This will bring up a summary of the country's naval forces currently deployed (not those under construction), as well as any bonuses or penalties currently in effect for a range of naval-related modifiers due to technology research. Directly underneath these values are the number of each type of ship, displayed as a silhouette, a naval designation for the ship type and a number.

Below that overview is a list of fleets, their type, name and location, as well as the number of ships in each fleet and its current mission. Left click on any fleet to select it. Right clicking on a fleet in this list will center the map on that fleet.

Naval Equipment List

Also in the overview are two small icons, Sunk ships button.png Lost Ships and Equip overview button.png Equipment Details.

Lost ships will open a window that lets you see a list of ships of the player that have been sunk in the last two years (it's time limited to help manage system resources).

Equipment details lets the player see the deployed ships not only by category (Carrier, Battleship, Submarine, etc) and quantity but also by ship class and quantity. This tool provides the player with information to let the player decide if a particular category of ship is made up of older hull types and could use newer class ships in that type, as well as help the player judge the overall make-up of his navy.


Docked fleet example

Fleets usually begin the game docked in naval bases, and are represented by a counter that indicates the total amount of individual ships currently in that base. Moving the mouse over the counter and holding it there for a moment will bring up a tooltip providing more information, including fleet names, average strength and organization for all of the ships in that base, and a count of ship types.

A faction's fleets in port are vulnerable to port strikes if that faction does not have air superiority over the continental region the port is located in. Fleets will be safer if they are based in ports that either have sufficient air coverage or are outside the range of enemy bombers.

Individual fleets may be selected by first clicking on that counter which will bring up the player's fleets on the left side of the screen, as shown in the screenshot where "Home Fleet", "Northern Patrol" and "2nd Submarine Flotilla" have all been selected with one click. To select an individual fleet, click on "Select". To select several fleets from this group, hold down ⇧Shift and click on "Select" for each fleet to be added to the selection. The fleet list will be reduced to only the fleets selected in this manner when ⇧Shift is released.


Once a fleet has been selected, it can be assigned an Admiral by clicking on the empty silhouette in the picture frame. This will bring up a list of available admirals to choose from. Fleets with admirals will perform better than those without, so it can be valuable to ensure as many fleets have admirals as possible. If there are no existing admirals available, new admirals can be recruited at a cost of 5 times the current number of admirals that country has in Political powerpolitical power.


Admirals have a skill between 1 and 9, where each level gives the Admiral 3 random skill points. These points are divided between

  • Damage, increasing the damage done to enemy ships by your weapons,
  • Defense, increasing your ships' defense against enemy attacks,
  • Maneuvering, increasing you fleet's retreat speed and positioning, and
  • Coordination, increasing the fleet's efficiency when performing missions.

The following table shows how much XP is required to gain skill levels:

1 2 3 4 5 6 7 8 9
XP Required 100 200 400 800 1600 3200 6400 12800 25600


Each Admiral may have a number of traits, represented by medal icons. These traits may be divided into two main groups: Personality Traits (which come with the commander and may not be earned) and Earnable Traits (traits which may be learned as the commander engages in battle).

With the Man the Guns DLC enabled, Admirals may be given Assignable Traits based on what Personality and Earned traits they possess.

Personality Traits[edit]

Trait Effect Action required XP required
Old Guard.png Old Guard −25% Leader experience gain Not gainable.
Media Personality.png Media Personality +10% Fleet Attack and Defense if commanding the Pride of the Fleet Not gainable.
Career Officer.png Career Officer +10% Commander Experience Gain Not gainable.

Earned Traits[edit]

Trait Effect Action required XP required
Sea Wolf.png Sea Wolf +20% Submarine Attack At least 80% are submarines. 700
Blockade Runner.png Blockade Runner +20% Retreat decision chance
+25% Fleet speed while retreating
Is retreating. 700
Superior Tactician.png Superior Tactician +25% Number of ships in the first contact Is winning. 700
Spotter.png Spotter +10% Spotting chance Gains 10 XP on spotting. 700
Fly swatter.png Fly swatter +10% Naval AA attack Is fighting air units. 700
Ironside.png Ironside +10% Capital Ship Armor Fighting with Capital Ships against Capital Ships. 700
Air Controller.png Air Controller +10% Sortie efficiency
+10% Naval Air Targetting from Carriers
Has carrier air wings on missions. 700

Repair Priority[edit]

Fleet Repair Priority.jpg
These icons allow the player to set the level of damage your fleet will sustain before attempting to return to base automatically to repair. Low means the fleet has to be practically sunk before considering abandoning the mission. Average allows the fleet to return if it sustains moderate damage. High means that the fleets will return to base if light damage is sustained, paintwork is scratched or barnacles are spotted growing on the hull. When the fleet returns to its home base repairs will take place automatically.

The speed at which ships are repaired is determined by the size of the naval base, the amount of ships that are damaged and being repaired at the same time, and the severity of the damage. Naval bases repair 0.075 HP (Number Needs Verification) worth of ships per level of base per hour, divided evenly between all ships docked at that base for repairs. Once damage is repaired, the fleet will automatically return to the patrol area and resume the mission. Detached parts of fleets that had the 'detach damaged ships' option selected will automatically re-form with their parent fleet as long as that parent fleets orders have not changed.

Other Repair Options[edit]

Repair now.png
The player can also choose Repair Now! to send your fleet back to base immediately. Clicking on this will cause the fleet to stop its current mission, return to its home base and repair. After repairs are complete the fleet will return to the patrol area and carry out its mission. Ctrl-clicking on this icon will send the fleet back to base immediately to be repaired and it will abandon its mission and stay there once repairs are complete. This button will also appear on the right of a ship name if that ship has sustained damage. Clicking it will detach it from the fleet, and send it to the nearest base to repair. Shift-clicking on the button will allow multiple damaged ships to be detached as one fleet.
Never repair.png
Never repair will turn off the auto-repair feature and the fleet will ignore damage and continue its task until the last ship disappears under the waves.
Automatic split off.png
Automatic split off is a toggle. If enabled, ships that are damaged will leave the main fleet and return to base to repair while the main fleet continues on its mission in the patrol area. Once repaired, those ships will return to the patrol area and merge back with the main fleet. Since there is a risk that lone or small groups of ships could be intercepted on the way to or from port, this feature is off by default. The safest time for using this option is when patrolling the region immediately outside of the fleet's home base.

Rules of Engagement[edit]

This toggle switches between Fire at will.png ‘Fire at will!’, where the fleet will engage any hostiles it encounters and Do not engage.png ‘Do not engage’, where the fleet will seek to avoid combat. It's worth noting that fleets that are assigned orders should not have ‘Do not engage’ selected, otherwise they will simply run every time they encounter the enemy. Also, fleets assigned a specific order such as “Convoy Raiding” will not try to engage enemy warships on patrol, even if their Rules of Engagement are set to ‘Fire at will!’ but instead they will prefer to sink convoys.

Fleet Management[edit]

Sometimes the makeup of the player's fleets should be changed to add or remove ships. There are several ways to do this.

Dragging cruisers from 3A Squadra to 6A Squadra

Dragging Ships Between Fleets[edit]

Select Ships to Transfer Popup.jpg

To transfer ships between existing fleets one must select the fleets. Remember that if there is more than one fleet in the base the player can use the ⇧Shift key to narrow down the selection of fleets selected. Then the player can simply drag a class of ship from one fleet to the next by using the mouse. Click on the silhouette of the ship class the player wishes to move and drag the silhouette to the destination selected fleet. Once there release the silhouette and a new pop up box will appear called "Select Ships to Transfer". This will let the player specify if they wanted to move the entire class of ships or only a smaller set of ships from that class to the new fleet.

You can repeat these steps for different classes of ships until the fleets have the composition you want.

Creating a New Fleet[edit]

Another way to manage one's fleets is by using the Create New Fleet.png "Create New Fleet" Button which the player can find when any fleet is selected. This lets the player take ships from the currently selected fleet and assign them to an entirely new fleet. It's worth pointing out again that unless the player specifies a naval base or a destination fleet in the production screen when producing ships, the game will automatically generate a fleet and all newly produced ships will be assigned to that fleet. However the player can use this button to create smaller, more specialized fleets from that automatically generated "reserve" fleet. When the "Create New Fleet" button is pressed a "Select Ships to Transfer" window will pop up allowing the player to specify which ships you wish to move to the new fleet. Once finished the new fleet will appear in the player's list of fleets with a generic name, like "Italy Fleet 1" for example.

Merging Existing Fleets[edit]

One can merge existing fleets by selecting the fleets in question by pressing the Merge.png Merge Fleets button located at the top of the player's selected fleets and to the right of the fleet mission selection icons. The selected fleets will immediately merge together into a single fleet. Hot key is [g] (group).

Ship Details[edit]

Left clicking on a ship silhouette in the fleet will bring up its ship details. From here its statistical values are visible, along with any combat history on the second tab. It is possible to rename the ship by pressing its name. Carriers will show the attached air wings. Reorganizing air wings is done through the air wing management system. To scrap/disband a ship press the red trash bin in the upper right corner of the ship detail screen, this will return its manpower to the pool and is an alternative to sending old ships off on suicidal missions.

Carrier Air Wings[edit]

When building a carrier, the player has the option to pre-define how its air wings should be organized. Only carrier (navalized) aircraft may be based on carriers, and must be researched and produced separately from their ground based counterparts. The air wings of existing carriers can be adjusted by selecting the air wing in the air force overview or by selecting an air region in the air map mode, which brings up a list of all bases, and then selecting the fleet the carrier is a part of to bring up the air base windows for all carriers in that fleet. From the (carrier) base window the process is identical to establishing or modifying a wing stationed at an air base. Pay attention to the aircraft capacity, as carriers can have uneven capacity. The maximum amount of planes allowed on an aircraft carrier without any penalty is determined by the deck size of the carrier(s). This is much smaller than bases on land - ranging from a capacity of 45 (1922 base model CV) to 85 (1944 base model CV), and up to 31 higher with +5 deck size variants. The act of exceeding a carrier's deck size (plane limit) is known as carrier overcrowding and it results in a significant penalty to carrier plane missions.

Viewing Combat Statistics[edit]

Fleet information, history and details

Hearts of Iron IV tracks experience, skill and history for individual ships, and this can be seen in the Fleet View. Select the fleet which the player wants to review. You will notice that each individual ship in your fleet is listed with a green organization and a brown strength bar, a silhouette for the ship class, a rank icon to show the ship's experience level, a vertical progress bar showing how much experience that ship has accumulated towards the next rank and the name of the ship. If the ship has participated in combat and sunk any enemy vessels, an additional icon appears History Report.png next to the ship name for history. Holding the mouse over this history icon will give you a summary of how many ships the player has sunk with this vessel. Clicking on the history icon will open the ship details pop up displaying the history of ships sunk for that particular vessel.

Strategy Fleet Composition[edit]

(NOTE: This is one out of many possible strategies)

Have 4 screen ships for every capital ship in a battle fleet. For example, a late war US carrier task group might have the ideal maximum number of 4 carriers(CV) (limited by management of airspace), 2 fast battleships(BB), a few battlecruisers(BC) or heavy cruisers(CA), and numerous screening vessels consisting of some light cruisers(CL) and 18+ destroyers(DD). In a battle, if there are more than four aircraft carriers on one side, for each additional carrier after the fourth (regardless of whether they are in the same fleet) the carrier air wings in the battle suffer a twenty per cent penalty on the number of aircraft that can be launched simultaneously (although this penalty will never reach 100 per cent). While there are no other "stacking penalties" on overall fleet size, there is an eight per cent penalty to hit chance for each additional ship attacking the same target. Accordingly, while additional non-carrier vessels can always be put to use, they will suffer efficiency penalties if facing enemy fleets that are significantly smaller than themselves.

In addition to large carrier or battleship-based fleets, a navy should use smaller fleets for specialized purposes, such as patrol fleets with 2-4 CAs/BCs, a few CLs and a bunch of DDs (20-30 works well), flotillas of 3-6 subs on convoy raiding or search and destroy missions, as well as squadrons of a couple DD for anti-submarine warfare, convoy escort, or convoy raiding. Destroyers are the backbone of the player's fleet. They are cheap, the best choice for dealing with subs, and able to torpedo enemy capital ships in favorable conditions when the enemy's screens are weak or absent. Always have DDs available for screening purposes and these other duties.

Light Cruisers are around 3 times as expensive as destroyers, but provide better surface detection allowing the player to find enemy navies/convoys faster, have more powerful torpedoes and guns while being almost as fast and evasive. A CL outclasses a DD in a fight and can enhance the effectiveness of a small destroyer task force. Heavy Cruisers and Battlecruisers are fast enough to support the player's screens in early skirmishes against enemy screens by using their superior guns to prevent a few dozen enemy destroyers from using hit and run tactics to pick off screen vessels a few at a time and exposing heavier vessels to torpedo attack. Battlecruisers are significantly more expensive than Heavy Cruisers, but have much higher range and firepower and are ideal for fast task groups and were used as surface raiders in both world wars.

Sea Regions[edit]

Navy map mode with regions and convoy routes.

The oceans of the world are divided into large strategic regions called Sea Regions. The player can view these regions more clearly by pressing the F2 key which will call up the names and highlight the thick black borders of these regions.

Sea Regions are subdivided into smaller areas which are equivalent to provinces on land. These smaller areas can be seen when the map is zoomed in, they are defined by a thin black border whereas the larger Sea Regions have a thick black border. While Sea Regions define where a fleet can carry out missions, these smaller areas allow the player to move a fleet to a particular spot on the map without a mission. This can be done by selecting a fleet, selecting Hold H, and right-clicking anywhere on the map within the fleet's range. A beige movement arrow appears and the fleet will move to that particular spot on the map and stay there. It will not carry out a mission however if it is detected by an enemy and combat ensues, it will act accordingly to the Rules of Engagement that are currently active. Such a fleet will also intercept any enemy moving through its immediate area, but not an enemy moving in nearby areas even if they are in the same Sea Region.

When this mode is selected one will also see friendly convoy routes which are represented by the dotted lines. The convoy routes consist of supply convoys that leave the player's home country to supply any overseas territories and armies, as well as resource convoys which collect resources from overseas territories and bring them to the player's home territory. Trade routes will also generate supply routes to or from the countries the player may be trading with. Those routes will last for as long as the trade deal is in effect. Supply convoys are fully automated and abstracted and the player does not have to worry about them, however, it is important to note which Sea Regions the player's trade routes pass through because enemy action in one of those regions could cause the destruction of convoy ships. When the player runs out of convoy ships, trade and supply can no longer occur efficiently which can result in loss of factory production or troop attrition and lost battles. Therefore it is important for a sea-going empire to familiarize itself with supply and trade routes and protect them with naval vessels.

Remember that fleets on a mission will carry out that mission in the entire Sea Region, and may also cover up to three contiguous Sea Regions per fleet.

Naval Missions[edit]

Assign Mission[edit]

Icons for mission assignment

To assign a mission to a fleet the player should first select that fleet. Once the fleet appears the player will see the icons (pointed at by the red arrow in the picture) to assign a mission to that fleet. These icons are PatrolPatrol (Z), Search and DestroySearch and Destroy (X), Convoy RaidingConvoy Raiding (C) and Convoy EscortConvoy Escort (V) and are used to choose a mission type for the selected fleet(s). There is also an anchor symbol, for HoldHold (H), which will order the fleet to halt its mission. Executing the halt command will not send the fleet back to base, it will just stop the mission and the fleet will then remain where it is.

Currently Assigned Missions

View Assigned Mission[edit]

The player can view which mission is currently assigned to a selected fleet by looking at the current mission box (highlighted by the red circle in the picture on the left). This icon tells the player which mission the fleet is currently assigned to perform. An anchor in this box means that this fleet currently has no mission orders. Fleets with no mission orders that are not docked will still follow the Rules of Engagement in the small ocean area where they are located.

Selecting Patrol Area[edit]

Selected Patrol Areas

Once the player has selected a fleet and decided which mission that fleet should carry out, they must assign that fleet to a patrol area somewhere on the map. To do this one must have their fleet selected and then right click on the Sea Region where one wants to carry out that mission. Each fleet can be assigned a single mission in up to 3 contiguous Sea Regions. Just keep right clicking on Sea Regions that touch each other or the original Sea Region. An error sound will occur if attempts to assign a fleet to more than 3 Sea Regions are made or to Sea Regions that are not next to each other. In the example on the right it can be see that "Home Fleet" is set to perform a patrol of these three Sea Regions: Western Approaches, Norwegian Sea and North Sea since the map shows those Sea Regions covered with green hatching.

Regular Fleet Movement

If the player wants to remove a Sea Region from the patrol area, he can do so by pressing ⇧Shift + right click on the Sea Region to be removed. ^Ctrl + right click will remove all selected patrol areas and force the fleet to move to the location clicked on without having a mission assigned to it. In the picture below it can be seen that "Home Fleet" will now move until it is off the coast of Norway, but it will not perform any mission. Units assigned to the map without a mission can still engage in combat if the enemy fleet detects them or happens to pass through their specific area.

Naval Mission Types[edit]

There are currently 5 naval missions in the game, each with their own purpose. Each mission has a "Formation Spread" which is how much the fleet has spread out over the mission area. The more the ships are spread out, the higher the chance they have to spot the enemy, but fewer ships will be able to join combat initially.


This mission Patrol.png will order the fleet to spread out into the assigned patrol areas in a very loose formation. This greatly increases the chances of detecting any enemy vessels in the assigned patrol areas however this comes at a cost. When an enemy is detected and combat begins, because the fleet is so spread out it's likely that only a few friendly ships will be in the initial combat. The ships will request assistance from the other fleet members in the patrol area, however it will take time for the rest of the fleet to arrive at the battle location and engage the enemy. This could prevent an effective engagement with the enemy force or, worse, could allow the enemy damage or sink ships in the initial encounter before the rest of the fleet arrives. The "Formation Spread" for this mission type is 160%.

Search and Destroy[edit]

Search & Destroy Search and Destroy.png is a naval mission that attempts to find and eliminate a hostile fleet. This mission keeps a fleet in a "Tight" formation which allows the fleet to be able to concentrate its firepower on enemy ships earlier in a battle than with other formations. A "Tight" formation makes it easier to bring ships into battle more quickly at the expense of being able to find hostile ships. Naval engagements normally start off with just a few combatants involved. As the naval engagement continues, more and more ships from the sea zone will join the fight. A higher Search & Destroy rating speeds up the rate that friendly ships join the fight. This helps a navy win the "firstest with the mostest" race. The Search & Destroy rating can be increased by researching the appropriate Naval doctrine. The "Formation Spread" for this mission type is 50%.

Convoy Raiding[edit]

This mission Convoy Raiding.png assigns a fleet to look for enemy convoys in the assigned patrol areas. Although the fleet can be engaged by enemy fleets if it is detected, fleets assigned to this mission prefer to avoid combat if possible except against convoys. This can be reinforced by selecting Do not engage.png 'Do not engage', which will make the fleet retreat from combat with enemy fleets (but still allows a fast enough fleet to attack convoys). Convoy raiding can target enemy convoys of all types - trade convoys, reinforcements convoys, lend lease convoys, troop convoys carrying enemy units ( both redeploying and invading ) and domestic resource convoys. Note, however, that one will only be able to target enemy convoy routes that are active with convoys on them - if enemy overseas units for example have enough local supply to sustain them the convoy route won't have any ships assigned to it, and thus nothing for the convoy raiding fleet to attack. The "Formation Spread" for this mission type is 120%.

  • Note: Raiding Coordination is a value that controls how quickly other submarines or surface raiders in a fleet on a convoy raiding mission can gather and help in the attack once an enemy convoy has been spotted. This value also controls how quickly the raiders can get away when enemy ships arrive.
Convoy Escort[edit]

This mission Convoy Escort.png lets a fleet protect friendly convoys in the assigned patrol areas, allowing them to concentrate on enemy submarines and commerce raiders that dare to attack your shipping. The mission is primarily a counter to Convoy Raiding. While using this mission type the player can still be engaged by other fleets however a fleet assigned to convoy escort will tend to avoid combat unless specifically protecting friendly convoy ships or identified and engaged by an enemy fleet on 'patrol' or 'search and destroy'. This mission is particularly important for covering invasions and troop transfers, as fleets assigned to Patrol or Search and Destroy will not necessarily come to the aid of a convoy under enemy attack. The "Formation Spread" for this mission type is 90%.

  • Note: Escort Efficiency is a value that indicates how quickly a fleet on a convoy escort mission can gather and help in the defense of a convoy once an enemy raider has been detected. This counters an enemy's raiding coordination. The higher the escort efficiency, the more screening ships (destroyers and light cruisers) are involved in protecting convoys. An increased escort efficiency score also helps prevent troop transports being sunk.

This option Hold.png orders a fleet to abandon any mission it was on and hold position, or to be sent immediately to a specific naval province by a right-click (this can be used to move a fleet away from danger or towards a trouble spot). It is often used for conducting shore bombardment in support of combats in adjacent coastal land provinces or for the use of Fleet Carrier air wings away from the fleet itself (for example, stationing a carrier force off the coast and then ordering its air wing to undertake separate Air missions like air superiority, naval strikes, port strikes or ground attack over the neighboring land region).

Missions on the Map[edit]

Icons in Patrol Areas

Patrol Area Icons[edit]

When a fleet is on a mission in a patrol area (which can include up to 3 adjacent Sea Regions), the fleet counter disappears from the map and a mission icon appears in the Sea Regions being patrolled. These mission icons are the same as the ones used to assign the mission to allow for quick and easy identification of the mission type occurring in that patrol area, and the number underneath the icon tells the player how many fleets are currently performing that mission in that area. For example in the picture it can be seen that in the North Sea Sea Region there are 2 fleets doing Patrol Patrol.png , one fleet is doing Search and Destroy Search and Destroy.png , two fleets are doing Convoy Raiding Convoy Raiding.png and one fleet is doing Convoy Escort Convoy Escort.png .

Select Fleets from Patrol Area Icons

If the player clicks on any one of these icons they will get a list of the fleets performing that mission in that Sea Region or a "Select All" button. One can select all the fleets doing that particular mission by clicking "Select All" or one can select individual fleets by clicking on the fleet name of the fleet you wish to select. One cannot select a group of fleets in this manner, it is either all or just one.

Shore bombardment[edit]

Bombardment of Chinese forces

Shore bombardment is not exactly a mission. In order to perform bombardment of any enemy land forces in a coastline province, all one has to do is move a fleet containing Capital Ships to the sea area next to the land province the player wishes to bombard, and keep it stationary there with "Hold" Hold.png mission. The bombardment penalty will automatically be added to combat in the coastal land province when the capable fleet is in adjacent sea province. The maximum bombardment penalty is 25% and is proportional to the number of appropriate ships in the fleet. Range of the ships is not a factor. Bombardment will include the shoreline provinces only. Battleships and Super Heavy Battleships add the greatest amount to the bombardment penalty, followed by Battlecruisers and Heavy Cruisers.

Ship Type Bombardment Penalty
Heavy Cruiser -4% Attack/Defence
Battlecruiser -8% Attack/Defence
Battleship -10% Attack/Defence
Super Heavy Battleship -16% Attack/Defence

(Note that these penalties apply to the enemy, and will stack up to -25%)

In the example, one can see the Japanese fleet of 7 ships including the heavy cruisers Izuomo and Iwate has moved off the coast of China and is within range to provide support to Imperial troops attacking 32 Juntuán. The player can confirm this by spotting the Shore Bombardment.png bombardment penalty icon under the Chinese general's name.

Naval Combat[edit]

When a country is at war and has a fleet deployed on the map either performing a mission in one or more Sea Regions or simply sitting in an ocean area somewhere, eventually they will encounter enemy naval vessels and combat will begin. Naval combat is fully automated to reduce micromanagement. One establishes orders and behavior for the player's Fleets and assign them to patrol certain areas of the map, with orders on how to behave when damage is received. However it may still be a good idea to check the player's naval battles once in a while, since this might give them clues as to the enemy's force disposition in that area, as well as insight into how their own fleets might need better organized to deal with it.


For a naval combat to happen at all, first one side has to detect the other side.

Ships can only detect other ships when they are in the same sea province, either stationed there on a Hold mission, or passing through on any other mission. Air superiority and radar coverage give a bonus to this chance, as described in the mission tooltip.

A land army division will detect any fleet on a Hold mission next to the land province it is in, but will not provide details of the fleet composition.

Any enemy fleet already in combat is also detected, and other fleets on missions in the region will move to join the combat.

When a fleet spots an enemy fleet, it can either start an encounter, or given "Do not engage" orders on a Hold or Patrol mission, not start it.

Naval Encounter[edit]

Naval combat has begun in the North Sea!

When an encounter occurs and enemy ships have been spotted, there will be an audio cue as well as informational icons on the screen. On the right side of the screen the player will see a flaming anchor icon with a red exclamation mark. This lets one know that a naval encounter has occurred in the region and that combat is in progress or it will begin shortly. If one clicks on the burning anchor, the map will center on the location of the combat encounter.

If defending fleet is on "Do not engage" orders, it will disengage immediately and the encounter will be over as soon as it has started.

Combat Location and Force Strength[edit]

Relative size of enemy fleets

When an encounter happens it means that ships from both navies have detected each other. It does not necessarily mean that all ships are currently engaged in combat. Depending on the orders assigned to either fleet some fleets may be out of position and currently avoiding combat until more of their fleet shows up. On the map you will see a display of relative fleet sizes in total number of warships. The number on the left represents allied warships, and the number on the right represents enemy warships. In the current example there are 8 allied warships against zero enemy warships. Clicking on this informational icon will bring up the naval battle box.

Naval Battle UI[edit]

Clicking on the icon on the map that shows the encounter and navy strength will bring up the Naval Battle popup screen. On this screen one will see the automatically generated battle name, the ocean picture will let you know if it is day or night and give you an idea of the weather as well. The player will see allied forces on the left, and enemy forces on the right, as well as the admirals leading the opposing sides, if any, and their skills. Beneath that one will see a colored bar showing relative strength. Holding the mouse over this bar will give more information as well as an estimate as to how long the battle will last.

Underneath the relative strength bar one will see a map with a dotted vertical line down the middle, and some ship icons. On the right and left side of this map there will be an area which might have ship silhouettes in it - this is the "out of range" area. It represents ships that are in the Sea Region and will participate in the battle and currently proceeding at full speed to link up and assume formation with the ships currently on the map.

Ships have both positioning relative to the enemy vessels, and weapon range. The dotted line down the middle represents a theoretical midpoint between the fleets, and the closer a ship is to that dotted line, the closer a ship is to the enemy's theoretical "side".

Fight or Flight[edit]

Commanding admirals of the fleets automatically make a decision to either engage immediately, wait for more ships to reinforce, or disengage, based on relative strength of the fleets. The player cannot impact admirals decision, other than by setting his fleet to "Do not engage" mode, which will force all ships to disengage. Current behavior of each ship is displayed in a tooltip.

The admirals are brave fellows and are happy to engage any fleet up to 5x size relative to their own, taking into account ship classes. Relative estimated strength of different ship classes is best seen from test examples summarized in the table below (DD1, CL1, CA1, BC1, BB1 refer to various classes of 1922 ships, submarines follow different rules).

Fleet Will engage Will disengage
10 DD1 50 DD1 51 DD1
10 CL1 91 DD1 92 DD1
10 CA1 62 CL1 63 CL1
10 BC1 76 CA1 77 CA1
10 BB1 52 BC1 53 BC1

Solving these examples gives estimated "admiral's opinion" of different ship classes: CL1 ≈ 1.82 DD1, CA1 ≈ 2.26 DD1, BC1 ≈ 3.45 DD1, BB1 ≈ 3.62 DD1. (Please note, exact formula is not yet verified from the game files).

From player strategy point of view this means that if you see enemy fleets repeatedly disengaging, it means your fleet is too strong. Try to limit it to only 5x of the enemy fleet you are trying to catch, or use naval bombers.

Naval Battle[edit]

Ships from both fleets proceed to close in to their maximum fire range with their maximum speed.

When in range, every hour a ship attempts to hit the closest enemy ship, damaging organization and hit points when successful. Success chance and resulting damage are based on ship statistics.

Ships that have lost all organization, or at least 50% of hit points (sometimes more) will attempt to disengage with other friendly ships providing covering fire. Enemy ships will try to finish off runners as long as they are still in range, and even chase them when possible. Better speed helps a lot to escape the combat rather than sink, and also to catch runners. Although even when disengaging ship would not be able to escape based on its speed alone, it still has a chance to leave combat each hour, and takes about 12 hours on average to do it.

The battle ends when one side was either fully destroyed, or disengaged. Surviving fleets return to their assigned missions, or depending on orders could head back to port for repairs.

Convoy defense battles end as soon as all military ships disengage, even though convoys with their speed of 10kn have no hope of running away from even the slowest military ship. This behavior is not yet confirmed to be intended or a bug.

Example Naval Battle[edit]

Battle against German convoys in the North Sea

Let's consider an example battle against German convoys.

In this case we currently have 8 destroyers which have spotted 3 German convoys. On their way are 1 aircraft carrier, 5 battleships, 3 battlecruisers, 1 cruiser, 6 light cruisers: and 1 additional destroyer. The Germans are not expecting any reinforcements. The bar is all the way to the right which means the friendly strike group is very unlikely to lose this battle against German convoy ships.

The German convoys are almost right up on the allied side as far as they can go. This represents a very bad position if one is an unarmed convoy ship facing armed enemy warships. So we can expect that the convoys will try to move out of range, to the right.

In the meantime, the group of 8 destroyers are the ships that spotted the convoys. They are not within firing range, and thus far from the midline. They will need to turn and speed towards the convoy ships in order to engage, because destroyer weapon range is not all that great. Now depending on how the AI logic that governs the battle determines it gets a better outcome, the destroyers might head straight for the convoys without waiting for other friendly ships. Or if the AI figures it could out-number the destroyers it would wait for other allied ships to enter formation before attacking.

Begin attack!

Now the game is advanced a few hours so that the player can see what is happening. In this second picture, we can see that the destroyers have closed position towards the German convoy ships. The convoy ships are trying to get away, however a 10 knot merchantman cannot hope to outrun a 30 knot destroyer. It simply won't happen. The player can see that the AI correctly decided that the merchantmen might be tackled without reinforcements. If the player will notice, the rest of the allied fleet has inched closer to the battle map, however it's likely that this battle will soon be over before they ever get in range, especially since the destroyers have already begun firing from their optimal position, the dotted line in the middle of the map.

Note that all ships have status bars on top of them. The solid green bar represents full organization and the solid brown bar represents full strength. These bars represent an average if they cover more than one ship. In the first picture of this battle, the convoy ships are at full strength. In the later picture, the convoy ships' strength is dropping as they take damage. In this picture the mouse pointer is being held over the 8 friendly destroyers however due to the way screenshots work, the cursor itself is not visible. But one will see that additionally a blue arrow appears pointing from the destroyers to the convoy ships. This represents the group which the destroyers are currently firing at, which is what caused the damage. Also a tooltip pop up has appeared to the right of the combat box showing the actual numbers involved in the combat calculation, for those who are interested. While this information is not so important in such a small battle as this against a harmless opponent, the player can use the information in this box to help determine who is dealing damage to who in their fleet so that they can create more efficient fleet compositions in the future.

The first merchantman goes down.

By advancing the game a few more hours it can be seen that the allied destroyers have claimed their first victim, and a nameless merchantman now rests on the bottom of the North Sea, which in this case is the box on the bottom of the screen that represents sunk ships. Quite obviously there haven't been any casualties on the allied side and they remain in optimal position and gun range. In fact the remaining two merchant vessels are also quite severely damaged. So despite the rest of the fleet being far, far out of range, it looks like this battle is almost over. It's important to note also how the relative strength progress bar has shifted in this new screenshot. It's now quite obvious that the allies will win this battle.

This battle is over.

A mere two hours later, all convoy ships are sunk. The player is back onto the map screen because the naval combat box disappeared, and they're left with this little icon that tells us that convoys have been sunk here. It's important to note the little gold star above the convoy ship. This means an allied victory, so enemy convoys have been destroyed. Had there been a skull instead of a star, it would mean enemy victory - or that allied convoys had been sunk.

The Fleet I assigned to the North Sea was assigned to Search and Destroy. The intention was to intercept any enemy warships trying to operate in the North Sea. However the game will take advantage of any targets of opportunity such as convoy ships, and sink those as well. Next let's look at a real naval battle, against opponents who can fight back.

If you click on this icon the player will get to the battle summary screen which they will go over in the next section. First, let's go pick a fight.

GER Naval Combat 1.jpg In this initial phase of combat, the entire allied fleet has arrived in formation. The German fleet, on the other hand, is still waiting on reinforcements and has many ships still outside the combat area. This does not bode well, because the allies have an aircraft carrier in this battle group and the aircraft have already started to attack the German battleships.
GER Naval combat 2.jpg A few hours have passed and the player can see that the organization of the battleships (the green bar) is beginning to drop because they are under air attack while the rest of the German fleet moves up. The progress or relative strength bar at the top reflects a less than optimal result for the Germans.
GER Naval combat 3.jpg More time has passed and now the German cruisers have already begun to take damage from aircraft. The allied fleet is moving its screen ships into optimal position, while the German fleet continues to hold back and wait for reinforcements.
GER Naval combat 4.jpg Night has fallen. The allied aircraft are now red, since in WW2 carrier aircraft rarely operated at night. The German fleet continues to hold its distance and refuses to engage before reinforcements arrive. The UK fleet is now in position with screens deployed ahead. Note the serious damage to German capital ships from carrier air forces alone. Also at this point pay attention to the distribution of forces. The UK has 14 submarines positioned on the bottom of the map - those submarines are undetected and not currently engaging in combat. However the Germans have suspected something and dispatched 2 destroyers to the bottom of the map to deal with this "separate" submarine threat - which leaves fewer screens for the capital ships at the top.
GER Naval combat 5.jpg It's morning again and the air battle begins anew. But this time the German fleet manages to shoot down some allied aircraft with its air defense guns while waiting for the rest of the fleet to move up.
GER Naval combat 6.jpg Finally! Most of the German fleet has now arrived into the combat area. German air defenses on the ships have managed to take out more aircraft, although they have continued to suffer damage. The submarines, however, are still far away, and considering the progress bar, the odds are still stacked highly against Germany so it's likely the AI will wait for those additional U-Boats. After all it's almost night-time again and allied naval aviation does not fly at night!
GER Naval combat 7.jpg The U-Boats are almost here. Notice how the German Anti-Submarine Warfare group at the bottom of the screen has grown to include 6 Destroyers, 4 Light Cruisers and 1 Cruiser. These ships have been split from the main fleet and will not be able to serve effectively as screens for the larger Battleships. Also notice the tooltip info box. It is informing them that the Germans have shot down 4 fighters. It also tells them that the fighters have done some damage to the German warships. Holding the mouse cursor over the different ships or aircraft on the map will give the player additional information about damage inflicted or received by those elements. Notice that in typical North Sea fashion, the weather has turned foul which hampers both air and naval operations.
GER Naval combat 8.jpg Now by holding the mouse cursor over the German battleships they can see the damage they have taken, the number of critical hits inflicted, as well as the aircraft that have been shot down by those vessels. They are still waiting on the U-Boats. Last radio message from Squadron command is that they will be here in 6 hours.
GER Naval combat 9.jpg Command has signaled that the U-Boats are in position and German ships are to begin the attack. German ships race towards the middle of the map which represents their optimal positions. The battleships with begin firing with their huge guns, covering the smaller screen ships as these close in to add to the damage. The weather remains foul, grounding allied naval aviation, however the German navy is going into the fight badly outgunned and already critically damaged. We go forward!
GER Naval combat 10.jpg Another 4 hours have passed. The return fire from 5 British battleships is simply too much. The German capitals are forced to retreat or face annihilation. A salvo of plunging fire finds the magazine of a German light cruiser and rips the ship apart. To add to the dismay, the weather has broken enough for allied naval aviation to resume attack from the skies.
GER Naval combat 11.jpg 3 hours later, and a German cruiser is also sent to the bottom, as well as 3 destroyers unlucky enough to be too close to the allied battleships who switched targets as the German capitals managed to maneuver out of range. In the meantime a single U-Boat manages to launch a torpedo attack at a passing allied battleship. The submarine is instantly detected by allied screens, losing its bonus.
GER Naval combat 12.jpg Another 6 hours, and the carnage is almost complete. 8 U-Boats have been sent to the bottom by efficient allied destroyers after achieving no kills. The screens protecting the German capital ships have been torn to shreds, the casualty list now standing at 7 destroyers and 2 light cruisers. And while allied naval aviation did sustain losses, losing half of their fighters as well as some torpedo and dive bombers, it's not enough. And with the German cruisers at the bottom of the North Sea there is virtually no air defense for the remaining crippled capital ships. In the meantime their anti-submarine group at the bottom of the battle map has detected all allied subs and prevents them from attacking our moribund capitals, but so far have not succeeded in sinking any.
GER Naval combat 13.jpg 4 more hours. The storm continues to rage around the battle. That and oncoming night grounds the British planes. All but 3 German U-Boats have been sunk, the others staying undetected under the pounding surf. In the meantime their anti-submarine ships finally manage to trick a few allied sub captains and a few salvos of depth charges send 2 British subs to the bottom. Their final capital ship desperately attempts to evade the allied fleet using the cover of night and the weather.
GER Naval combat 14.jpg After another night of fighting, their battleship is finally sunk by the numerous and crafty Brits, and now they turn their attention to their anti-submarine squad, which has had more success during the night, sending another 4 British subs to the bottom. Their submarines remain out of sight. Are they even there?
GER Naval combat 15.jpg Another day and a half passes. The cruiser that was screening the German anti-submarine squad is sunk. All but one allied submarine is destroyed. The Brits decide they've done enough carnage and begin to break off. The crippled remains of the German fleet agrees and out of ammo and spirit, break for the Fatherland.
GER Naval combat 16.jpg Oh no, it was a ruse! Those crafty Brits disengaged their main ships, but sent their lighter screens after the remains of our anti-submarine squadron! I expected no less from the Royal Navy.
GER Naval combat FINAL.jpg Finally, the battle is over. There is nothing left to do but mourn their electronic dead. Out of their glorious German fleet, only 10 ships remain. The only British losses: 11 submarines, 7 fighters, 3 torpedo bombers and 4 dive bombers. A mere pittance compared to the millions of Reichsmarks but more importantly, tonnes of precious steel, oil, chromium and thousands of man hours that were wasted. For nothing. You have been ordered back to Berlin.

As was mentioned at the beginning, Naval Combat in Hearts of Iron IV is mostly automated. The work must be put in before the fight, by organizing one's fleets into appropriate sizes and with enough screens. One should think a little about the specific areas are best to be controlled and what one hopes to achieve. Land based aviation, for example, can have serious consequences for the unwary navy especially as the war drags on and technologies improve. Remember that the goal of the Navy is not necessarily sink enemy ships. There is no glory in having sunk tonnes of warships if the player loses the war. And those variables Paradox has chosen to leave to the player.

Detailed Naval Combat Results[edit]

The button to access the detailed naval combat results is at the bottom-left of the standard naval combat results window.

It is possible to get detailed and valuable information on the impact of various elements of the player's fleet during a naval combat, once that combat has finished. After bringing up the naval combat results screen, access the detailed information by pressing the detailed naval combat results button, indicated in the picture on the left. This button acts like a toggle, so once it has been pressed in the current session, the naval combat results will automatically display the detailed results unless the detailed naval combat results button is pressed again.

The British had the better day here, but still suffered significant damage at the hands of the Italian navy.

Once it has been pressed, it will bring up a column of information on either side of the summary naval combat results window, showing the impact of each unit or air wing (both carrier or land-based) on the battle - see the example to the right. In this case, the battle didn't include an air component, but the player can see from the sample results screen shown below that for the Italians, the heavy cruiser Marco Polo delivered the final hits to the British destroyers Wishart and Wrestler, but it was assisted in sinking them by a number of other Italian ships, including Giuseppe La Masa, Giacinto Carini and Castelfidardo. On the British side, their heavy cruiser Effingham also did finished off two enemy destroyers (Curtatone and Castelfidardo) but the light cruiser Caledon did almost as much damage (but only delivered the final hit on one enemy ship).

As will often be the case, in this example there is more information available in the detailed results than can fit on-screen in the columns. To view the performance of the rest of the vessels involved in an encounter where the detailed results won't all fit on screen at one time, use the scrollbars on the side of the detailed naval results column.

Carrier Capable Aircraft[edit]

In order to be able to base aircraft on an aircraft carrier, carrier capable models must be produced. To do this, first the land based version of an aircraft will be researched, then one must research the carrier capable version by clicking the aircraft carrier button on the aircraft type in the air research tab.

Research carrier capable version button

This can only be done for Fighters, Close Air Support and Naval Bombers. The carrier capable version has a different model name than the land based version, as well as different artwork and different stats. If one doesn't intend to use aircraft carriers, then one does not need to research carrier capable planes.

When a new carrier is produced, the planes that will originally be based on it are produced as part of the carrier production line in the naval section using dockyards. It will produce the most up-to-date models researched. From the carrier production line one can change the types of planes that will be produced and deployed with the new carrier when it is launched. If there is need to replace these, then one will need to set-up a new aircraft production line using military factories, and select the appropriate carrier capable model.

When an aircraft carrier is part of a fleet which is on patrol in one or more regions, then the wings based on it are shown as on a carrier mission. They will operate as a Carrier Air Group and automatically take part in any naval combat if the fleet engages or is engaged by the enemy, and the carrier is within range. There is no need to give them any specific orders.

If one wishes to use one's carriers as a floating air base, and use the wings to operate standard air missions, then they will no longer operate automatically as a Carrier Air Group. If the carrier fleet is engaged by the enemy it may not have air cover. The player should be careful to make sure that it is properly protected. One might place a fighter wing on an interception mission in the region where the carrier fleet is located, but send a bomber wing to target an adjoining region, for example to support an amphibious landing.

Naval Bombing Missions[edit]

A discussion about naval bombing missions can be found in the Air warfare section, to include the use of naval bombers, TAC air, and close air support in naval strikes (reference Air warfare#Naval Strike) and port strikes (reference Air warfare#Port strike).

Naval combat details[edit]

  • Armor in naval combat does not work the same way as armor in land combat. Rather, the damage prevented is calculated as a proportion of the difference between the defender's armor and the attacker's piercing. At the extreme, if a defending ship had at least 1 armor and the attacker had piercing of zero, then 90 per cent of the damage would be prevented. On the other hand, if a defending ship was attacked by another ship with a piercing value at or higher than their armor, then none of the damage would be prevented, with the damage done for situations in-between scaling to the difference between the defender's armor and the attacker's piercing stat. The formula is: attack multiplied by (1 - 0.9*((armor - piercing)/armor)), but the armor minus piercing cannot be less than zero.
  • In naval combat screens (destroyers and light cruisers) are generally targeted first. Having enough screens to shield your capital ships from fast, torpedo-carrying destroyers and light cruisers is important as those torpedoes ignore battleship armor.
  • Torpedoes fired from screens have a range of just four kilometers, so screens can only use them against other ships if they get very close. The only exception to this is for Japan if they have the 'long lance' idea (unlocked through the naval branch of their national focus tree), which doubles their torpedo range to 8 kilometers.