- This page deals with naval combat mechanics. For information on the recruitment and maintenance of navies see navy. For details about ship types see naval units. For the state of war see warfare.
Naval warfare is the competition of sea-going power between nations at war. While a majority of warfare is land-based, the naval aspect of conflict can be incredibly influential in the spheres of trade, colonisation and conquest.
- 1 Sea battle interface
- 2 Engagement width
- 3 Combat sequence
- 4 Combat statistics
- 5 Morale and strength
- 6 Naval doctrine
- 7 Fleet actions
- 8 Naval missions
- 9 Strategies and tactics
- 10 Footnotes
Sea battle interface
Like land warfare, naval combat occurs when opposing fleets confront each other in the same sea province. Also like land battles, these sea battles can go on for many days, so they should be considered not as a single engagement, but as two fleets maneuvering to gain wind, standing off and skirmishing before the fleets finally collide.
In EU4, there is no player involvement inside combat, but the interface now displays more information, showing among other information which ship is fighting which. The naval combat interface shows the strength of the two fleets engaged in the combat. Combat will begin with a contest of firepower, followed by shock action in which ships attempt to grapple or ram one another. This sequence will alternate until one of the fleets loses morale and is either routed or destroyed. The condition of each ship is expressed as a percentage, and hovering over a ship with the mouse cursor will produce a tooltip which identifies which opposing ship they are currently firing on, as well as their current morale, their strength, and the ship type.
Since the patch 1.16, combat width for naval warfare has been introduced, it has a base of 25, and can be modified by:
- admiral's maneuver +10% per pip
- Coastal sea +10%
Heavy ships occupy 3 combat width, while galleys, transports and light ships each occupy 1 combat width.
Unlike the 'combat width' of land warfare, the 'engagement width' of the two participants are independent, that means one participant could have wider engagement width than the other.
Like land warfare, naval combat occurs when opposing fleets confront each other in the same sea province. Also like land battles, these sea battles can go on for many days, so they should be considered not as a single engagement, but as two fleets maneuvering to gain wind, standing off and skirmishing . A sea battle will last until one side is routed or annihilated. Patch 1.16 also introduced the concept of a naval combat width, and much like its land cousin it is the total number of ships that can engage the enemy at any one time.
While there is an ongoing naval battle, fleet's ship will try to populate its engagement width until the limit is reached, in the following order:
- Heavy ships
- Light ships
Any ships already disengaged will be ignored.
Combat is divided into a series of 3-day phases. Phases alternate between fire and shock, with the fire phase happening first.
In combat each ship will try to find a target and make an attack. Every enemy ship has a base chance of 10 to be picked as a target, further modified by:
- +0 to +5 random chance
- +5 if same type
- x0.1 if morale at 0 or less
- x2 if damage less than 50%
Enemy ship with best score is picked as a target. If the previous target is about to die, a new one will be picked.
At the beginning of each phase, each side rolls a die. The result is used to determine the morale damage and hull damage inflicted by that side during each of the three days of that phase.
Base damage is calculated according to the following formula:
Base Hull Damage = 0.025 + 0.025 * (2 + Dice + Combat Modifiers)
The amount of cannons of the attacking vessel affects the hull damage dealt and the hullsize of the defender decides how long it can stand the cannon fire.
The Artillery Fire Modifier gives a bonus or penalty to damage dealt depending on if attacker or defender has a technological advantage.
- Attacking unit modifier: The attack modifier from the attacking unit's technology, i.e. "Artillery Fire".
Artillery Fire Modifier = Attacker Artillery Fire - Target Artillery Fire
- Attacking unit Combat Ability: Any Combat Ability bonuses the attacking unit has.
Final Damage = 0.03 x Base Hull Damage x Ship Strength x (Cannons / Target Hull) x (1 + 0.05 x Artillery Fire Modifier) x (1 + Ship Combat Ability + Combat Ability from Admiral) / (1 + Target Ship Durability)
If target ship Morale is 0 or below, Final Damage is multiplied by 10.
Galleys fighting in the inland sea have their Final Damage doubled.
Morale is damaged both over time during a battle and also when a friendly ship is sunk.
Base Morale Damage = 0.25 x (Country Naval Morale / 3) x Base Hull Damage x Ship Strength x (Cannons / Target Hull) x (1 + 0.05 x Artillery Fire Modifier) x (1 + Ship Combat Ability + Combat Ability from Admiral)
Several ideas decrease the amount of morale lost when a ship is sunk:
Any ship with less than 0.5 morale will try to disengage from the battle. Whether it will be successful depends on the ship's Disengagement Chance. The base value of this chance is 3% but can be modified by some national ideas.
|Dip Tech Level||0||3||7||8||12||18||22||25||27||29||31|
|Morale of Navies||+2.0||+2.1||+2.4||+2.6||+3.0||+3.5||+4.0||+4.5||+5.0||+5.5||+6.0|
|Mil Tech Level||0||7||13||16||22||25||32|
The following contributes to the maximum morale of a nation's navy.
|Naval maintenance||20% at minimum maintenance (minimum of 0)|
|100% at maximum maintenance (multiplicative modifier)|
|Navy tradition||+25% at 100 navy tradition|
|Prestige||+10% at 100 Prestige, −10% at −100 prestige|
|Power projection||+10% at 100 power projection|
|Naval reformer advisor||+10%|
|Defender of the Faith||+5%|
|War exhaustion||−2% per 1 war exhaustion|
Certain National Ideas, Idea groups and policies will bump naval morale.
Each point of naval tradition also increases naval morale recovery by +0.10%.
Combat ability is a value that is multiplied with the units' damage dealt (both for casualties and morale), but only for the specified type of unit.
Heavy ship combat ability improvement
Light ship combat ability improvement
Galley combat ability improvement
- Transport combat ability improvement
- The combat ability of transports is not modified by the base game.
- Main article: Naval units
Hull is the defensive stat, and cannons the offensive stat. With the exception of Morale, every combat phase the hull/cannon pips are used against each other to calculate the number of hull damage of each combat phase.
Leaders are rated on a scale of 0 to 6 for each of the following skills:
The leader's skill is added to the dice roll of its respective phases.
The leader's maneuver affects the movement speed of the fleet both on the map and in battle. Each point also grants 5% additional trade power when assigned to a fleet protecting trade in a trade node. Finally, it reduces attrition taken by 1% per skill level.
Concluding a battle
A naval battle ends when one side is either:
- Reduced to 0 morale; or
- Flees from combat; or
Upon victory, ships from the defeated fleet may be captured, depending on the difference between the two fleets' maneuver skill. Generally very little to no ships will be captured for leaderless (0 vs. 0 maneuver) battles.
If the defeated fleet still has ships remaining, it will escape to the nearest friendly port to repair and recover its morale. Naval battles, like land battles, may cause war exhaustion as well as affect warscore, naval tradition and prestige. Note that warscore gained from naval battles will generally be insignificant compared to those gained by its land counterparts.
Several ideas increase the chance of capturing ships after a battle:
Morale and strength
- "Morale of navies" redirects here. For bonuses that increase naval morale, see § Max naval morale above.
Morale is an important factor in fighting battles. Each turn of combat a unit will take a Morale hit. Once a fleet's average Morale value has been reduced to zero the fleet will attempt to retreat. Retreat cannot happen until both a fire and a shock phase have completed, so a fleet that has its morale reduced to 0 before that point will be destroyed.
If a fleet loses a battle while having low enough morale, they will be forced to retreat to a port of the nearest sea province. While retreating, it cannot be engaged in combat or be controlled until it reaches the sea province, nor will it repair. The fleet will also move 50% faster, and will recover morale at a normal rate during the retreat.
After every battle is fought a fleet must spend some time not fighting for its morale to recover.
Every month when docked at a home port, a ship recovers a 10% of its maximum morale.
Certain National Ideas, Idea groups and policies will increase naval morale recovery.
Each point of naval tradition also increases naval morale recovery by +0.1%.
Unit strength is an important factor in fighting sea battles. Naval unit strength affects how long it can stand cannon fire before sinking. Each turn of combat a unit will take hull damage reducing its strength.
Galleys gain a bonus 100% strength in inland seas  which are shown on the map below in pale blue.