Naval warfare

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Navy, Fleets and Task Forces[edit]


Collectively, the player's ships are referred to as the navy.

For organisation and control, the navy is divided into one or more fleets. Each fleet consists of one or more task forces, with each task force containing a number of individual ships.

Task forces are the most basic unit of ship control available to the player, while fleets serve as a useful grouping mechanism for task forces. Orders may be issued to individual task forces, or to entire fleets at once.

At the beginning, the player's navy will already be organised into at least one fleet. The player may create new fleets and task forces at their discretion, and move ships between them.

The player can assign missions to each fleet or task force. If the player wishes for an entire fleet to perform the same mission, the mission can be set at the fleet level. Alternatively, missions can be allocated to individual task forces within a fleet, allowing different parts of the same fleet to perform different tasks.

Task forces[edit]

The unit overview of a carrier task force called "Singapore Squadron", part of the "Far East Command" fleet, docked in Singapore

In battle each ship can act individually to a degree. Outside of battle the task force is the smallest controllable naval unit on the map. Its stats are the averages of its ship's stats. The exception are speed (minimum) and fuel consumption (sum).

Task forces can be created and restructured in several ways. Newly built ships join the task force they were assigned or a reserve fleet. Existing fleets can be split in half or split in a custom way using the options above the task force's unit view. Selecting ships and right clicking another task force reassigns them there. Multiple selected task forces can be merged into one. Selected ships can be automatically distributed in balanced task forces, which attempts to create task forces with good ratios of screens, capital ships, and carriers.

To maintain the current composition even after a task force takes losses, the Automatic reinforcement option can be enabled. It will pull ships from the theaters reserve fleet to fulfill reinforcement request. The targeted ship counts are shown below the current ones. Finally the task force composition editor allows changing the desired number (and with Man the GunsMan the Guns the specialisation}}) of ships that will be automatically deployed to the task force.

Repair options[edit]

  • Automatic split off Automatic split off: Allows the most heavily damaged ships to detach and return to a close by naval base for repairs while the rest of the task force continues its mission. The detached ships are very vulnerable to attack while they return. After completing repairs, the ships will return to their assigned task forces. The amount of ships detached depends on the repair priority setting as well as the damage to each individual ship.
  • Repair priority Repair priority: Sets how severely a task force has to be damaged before it returns for repairs.
  • Repair now! Repair now!: Explicitly orders an individual ship to return to port as a detached task force for repairs. Shift-clicking on the button will allow multiple damaged ships to be detached as one task force.

Engagement rules[edit]

engagement rules The engagement rule controls how aggressive a task force behaves. For example on High risk submarines will attack all enemy ships, including screens.


(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.


The Atlantic Fleet assigned to two strategic regions. The top right shows the naval theater containing the fleet.

Fleets serve as a grouping mechanism for task forces.

An admiral can be assigned to each fleet, conferring bonuses to all task forces within the fleet. However, an admiral can only effectively manage a fleet containing 10 task forces or fewer. If this number of task forces is exceeded within a fleet, the admiral's bonuses will be penalised.

When a fleet is selected, the outline of the area it operates in pulsates. Strategic regions can be added and removed from the fleet's operation area by right-clicking and shift-right-clicking respectively.


Just like in land combat, fleets are grouped into theaters. A theater can have an increased alert priority, to give the player more notifications of what is happening. Each theater has its own reserve fleet.

The reserve fleet contains task forces that are not assigned to any particular fleet and have no active missions. They can either be manually moved into other fleets or, more commonly, their ships are used to fulfill automatic reinforcements from other task force.

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.

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.

Sea Terrain[edit]

Each Sea region belongs to a specific type of "sea terrain". While they give the same modifier to all ship classes, many shipclasses have additional penalties in one terrain type and buffs in others. Unlike land where each province could have it's own terrain, sea regions have the same terrain all the way through.

Ocean is simply the baseline. No vanilla ship has any modifiers in this terrain. That makes it the equivalent of plains, except on the sea.

Shallow water only has a slight penalty to positioning for everything, except for one shipclass: Submarines. Those have a massive increase to their visibility, which is easily their most important stat. So they should really avoid these regions.

Deep Ocean drastically penalizes mines. They are also a bad region for ships smaller then a heavy cruiser. Submarines seem rather unaffected to buffed however.

Fjords and Archipelagos The buff to visibility and debuff to positioning should just about cancel each out. However this is a poor terrain for anything bigger then a light cruiser, making them the mirror image of the deep ocean. Big ships additionally lose speed, movement and combat ability. They also get a large increase to fuel consumption - which is bad as those tend to already be gas guzzlers.


Missions can be assigned to task forces and determine how they behave in the context of their fleet. Most missions make the task force operate across the whole operational area of the fleet.


Cancels the current mission and moves the fleet to the closest port. Control-clicking the mission makes the task force stay in its current province. A task force on hold doesn't consume fuel. When positioned on a sea province, it can provide shore bombardment bonuses to adjacent land battles and block connections between land provinces (except the ones in Denmark). It can still engage in combat if an enemy fleet is on hold in the same province.


A German submarine task force in the process of being spotted by the British Humber Force.

A patrol task force operates in a single strategic region, so a fleet should have one for each region in its operational area to cover them all. They continuously operate in their respective region, looking for enemies. Once they successfully spotted an enemy they can call in strike forces to deal with it. The spotting progress starts at base spotting chance and increases by hourly change until it reaches 100%. If the hourly change would be zero or negative, the task force can't spot that enemy. The patrol can only start spotting enemy submarine forces with a probability of each hour. A patrol can only spot one enemy task force at a time and vice versa.

Strike force[edit]

A strike force will intercept enemy forces in the fleet's operational area after they have been fully spotted by patrol task forces. The rest of the time they stay in port to conserve fuel which makes this mission suitable for large battle groups.

Convoy raiding[edit]

This mission Convoy Raiding.png assigns a task force to look for enemy convoys in the fleet's operational area. The raiding force needs to spot the convoys before attacking them. Each raiding task force can only efficiently cover 1.5 strategic regions. If a fleet does not have enough raiding task forces for the area it covers, their efficiency will be reduced.

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.

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]

A 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

Any surface ships that are on hold in a province adjacent to a land battle provide a Shore Bombardment.png shore bombardment bonus. The bonus can be up to 25% (reducing the enemy's attack and defense), and bonus to bombardment (e.g. through traits) cannot go over this limit. Every point of heavy gun damage provides 0.1% bonus and each point of light gun damage 0.05%.


A battle gets initiated on a specific province between two task forces, one of them being the attacker. This usually happens after a spotting process is complete or opposing fleets move onto the same province. Naval and port strikes by air wings trigger a naval battle that lasts a single hour. Otherwise the battle lasts until one side is fully escaped or destroyed. The defender always joins the battle with full efficiency while the attacker may have a reduced efficiency depending on circumstances.

Inside of battles ships can behave independently and convoys, which are normally abstracted, are also present as individual ships.


  • Screening group: The screening group holds all the screening ships - usually light cruisers and destroyers - tasked with keeping enemy screening ships away from the main battle-line. Insufficient screening will allow enemy screens to make torpedo attacks against the battle-line.
  • Battle-line: The battle-line provides the main direct firepower of the fleet, usually in the form of battleships and heavy cruisers. They will also prevent enemy capital ships from firing at friendly carriers.
  • Carrier group: The carrier group provides the main long range striking power of the fleet. Screened from the enemy by both the screening group and the battle-line, the carriers can launch strikes on the enemy without interference. Should any convoys be present in the battle, they will also appear in this area.

Screening efficiency[edit]

The ratio of screening ships and other ships is the screening ratio. Optimal screening efficiency is reached when the ratio is 4. High screening efficiency prevents enemy torpedo attacks against the back lines and gives increased hit chance (up to +40%) and retreat speed (up to +20%) bonuses to ships in the battle-line and carrier group.

The ratio of capital ships to carriers and convoys is the carrier screening ratio. Optimal carrier screening is reached when the ratio is 1. High carrier screening efficiency further prevents enemy torpedo attacks (stacking diminishingly). It also provides increased sortie efficiency (up to +10%) to carries and increased retreat speed (up to +20%) for both carries and convoys.

Weapon cooldown[edit]

All weapons except torpedoes can fire every hour. Torpedoes normally fire every 4 hours (Man the Guns this can be reduced to 3 with the Drill Master trait).

Target selection[edit]

Each ship with offensive weapons (i.e. not carriers and convoys) and the respective weapons off cooldown can target three enemy ships independently per combat hour; one with its depth charges/light weapons, one with torpedoes, and one with heavy guns. Depending on weapon type and enemy screening, only certain enemy groups can be targeted.

  • Depth charges: the only weapon type that can target submarines, and only if they are revealed (see below)
  • Light guns: can only target the closest non-empty group
  • Heavy guns: can target the first two non-empty groups
  • Torpedoes: the probability that a torpedo can target ships past the screening group is 100% minus the enemy screening efficiency. To target ships in the carrier group (including convoys) it needs to pass an additional check of 100% minus the enemy carrier screening efficiency.

Submarines will only target screens when set to High risk engagement rule. They will only target capitals when set to Medium risk or higher.

Out of the remaining valid targets one is chosen by weighted random selection. If the firing ship is not currently running away, the enemies are weighted as follows (numbers in parenthesis for light guns)[1]:

  • capitals: 30 (2)
  • screen: 3 (6)
  • submarine: 4
  • carriers: 15 (1)
  • submarine vs convoy: 600 (40)
  • non-sub vs convoy: 60 (4)

If the target is lacking HP, up to +100% bonus are applied to the weight. If the enemy is escaping, the weight is reduced by 50%. If the enemy is actively fighting (i.e. not waiting), a +50% bonus is applied.

The weighting is similar when the firing ship is escaping but only considers targets that are actively fighting and always chooses the highest scoring target without randomization.


Submarines are completely immune to being targeted while they are hidden. This is indicated by the crossed-out eye symbol. Revealing a submarine sets a cooldown after which the submarine will hide again (unless the cooldown gets refreshed). There are three circumstances that reveal submarines:

  • If the submarine starts the battle on the defending side, it will be initially revealed for 16 hours. This typically happens when its task force gets spotted by enemy patrols.
  • If the enemy task force has any sub detection greater than zero, there is a 4% chance of revealing the submarine for 20 hours every time it attacks. The submarine's visibility increases the chance and bad positioning increases the visibility effect by up to 200%. Visibility and bad positioning can at most double the probability. It can be reduced with the Torpedo reveal chance modifier (Electric torpedo technology, various naval doctrines, Silent hunter admiral trait). The combined formula is
  • Every combat hour there is a chance for the submarine to get revealed for 20 hours passively by the enemy's sub detection (averaged across all enemy ships):

Hit chance[edit]

The base hit chance is 10%, 11% for depth charges. If the firing ship is lacking manpower or organization, the chance is reduced by up to -25% and -50% respectively.

Hit profile multiplier.png

Another factor is the guns hit profile compared to the target's profile. Small, agile ships are harder to hit, especially for bigger and slower guns. The hit profile of a ship is its surface/sub visibility multiplied by 100 and divided by its speed. Subs use their sub visibility, even when revealed. The hit profile of convoys is always 120. This profile is divided by the gun's hit profile (light: 40, heavy: 90, torpedo: 145, depth charge: 100) and then squared. It factors into the hit chance but can not increase it.

The hit chance can also be influenced by bad weather, night, screening bonuses, and the ship's admiral's level, logistics and planning skills.

Man the Guns Torpedo Expert and Destroyer Leader traits can increase the hit chance for torpedoes.

In practical terms, a 1% speed increase is the equivalence of increasing your ship's effective hp by 1.7%. This increase applies across the board regardless of your ship's sub/surface visibility or what weapon is being used against it.

The hit chance is always at least .05%[2].

If the hit chance doesn't result in a hit, the target remains unaffected.

Armor piercing[edit]

Whether a weapon can pierce the enemy's armor has a great influence on the damage dealt. If the piercing value of the weapon is higher than the enemies armor, it increases the chance of critical hits. If it is lower the damage will be reduced accordingly. Torpedoes ignore armor.

Outgoing damage[edit]

The respective weapon type damage of the ship can get modified by doctrines, the naval terrain, the weather, Pride of the Fleet if present, and the admirals skills and traits. Bad positioning can cause a penalty of up to 50%. The Defense modifier of the enemy admiral's skill level will also reduce the damage.

If the weapon can not pierce the enemy armor, damage is reduced by up to 90%, scaling with the ratio between the two.

The damage gets randomized by ±15%.

Damage is applied against both the target's HP and organization, but organization damage will be relatively low while the ship's HP are close to full.

Critical hit[edit]

A critical hit is a particularly devastating hit against the target which can also damage some of its critical components. The resulting penalties can only be removed by repairing the ship.

The chance for a torpedo to score a critical hit is 20%. For other weapon types the base chance is 10% but also depends on whether the armor can be pierced (doubling the chance) and the target's reliability (scaling down to 0% at 100% reliability).

Man the Guns The Marksman and Chief Engineer traits can respectively increase and lower critical hit chances, irrespective of weapon type.

If a critical hit does occur, it potentially affects one of the critical parts on the ship. The chance for this is 10%, inversely scaled by reliability (e.g. at 25% reliability the chance increases to 40%). If a critical part is hit the effects depend on the specific part. For example if the ammo storage is hit, the hit damage gets massively increased, while a hit to the rudder does only minor damage but cripples the retreat speed of the ship.

If a critical hit occurs without damaging a particular part, the regular damage gets doubled for torpedoes. For other weapons the bonus ranges between +100% (at 100% reliability) and +500% (0% reliability).

Naval strike[edit]

Every 8 hours (00:00, 08:00, 16:00) planes can sortie in the battle.

The number of external planes is limited to: <sum of all enemy ships' current HP> * 0.05 * (1 + 0.2 * <combat days>). But at least 20 planes can always join.

Target selection[edit]

The naval strike target is randomly selected from a weighted distribution. The base weight is each ship's maximum HP. This gets scaled depending on ship type:

  • revealed submarine: x10
  • capital ship: x50
  • carrier: x70

Damaged ships get a linearly increasing weight up to +500% at 0% HP. If a ship's anti air attack is below 5, the weight is increased by 5 * (5 - <ship/convoy AA>). For example convoys have only 0.2 anti air attack, increasing their score by 24.

Ship AA defense[edit]

When a ship gets targeted by an air wing, it will try to shoot back. Against non-kamikaze wings the ship's chance to shoot back is (90%+50%*(90% - 1%*<wing's agility>)) * 20%. If the attacker performs a kamikaze attack, the ship can always shoot back and its AA attack gets increased by 2. The highest possible number of planes that can be shot down is .5% of planes times the ship's AA attack. The effective number of planes shot down is a random number between 0 and this maximum. The losses are increased to 400% for kamikaze strikes.


If any planes remain after the ship shot at them, they perform the naval strike. If they are based on a carrier that takes part in the battle, their damage is increased to 500%. The ratio of planes that actually hit the ship is <naval targeting> * 30% (capped between 0% and 100%). It does not depend on the maneuverability of the ship.

The ship's AA damage reduction further reduces the damage dealt: 0.15 * (<ship AA (0 for convoy)> + 20% * <all ships fighting on same side AA>)^0.2

<ship AA> is 0 for convoys but convoy AA is included in <all ships fighting on same side>. The damage reduction can not exceed 50%.

Critical hits are calculated the same as a regular ship gun hit that pierces armor.

If the naval battle was a port strike, the naval base gets damaged proportionately to the damage dealt against the ship.

Carrier stacking penalty[edit]

Each carrier exceeding 4 per side incurs a 20% penalty, up to 80%. The penalty reduces the number of carrier wings that can operate.

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.

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, as well as the values of some naval-related modifiers. Directly underneath these values is a summary of ship counts by type.

Below that overview is a list of task forces with their name, current operation area, as well as the number of ships and current mission. Left clicking on any task force selects it. Right clicking on a task force centers the camera on it.

Naval Equipment List

Sunk ships button.png Lost ships will open a window that shows a list of ships that have been sunk, either of or by the country, in the last two years.

Equip overview button.png Equipment details shows the current number of ships by type and class.

  1. these numbers can not be modded
  2. but effectively it can't go lower than .1% due to the implementation