Naval warfare

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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.

Sea battle interface

The naval combat 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 (being the number of sailors still alive on that ship to fight) 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.

Engagement width

Engagement width.png Engagement width is the combat width for naval battles. Unlike the combat width of land warfare, the naval engagement width of the two participants are independent, that means one participant could have wider engagement width than the other. Heavy ships occupy 3 combat width, while galleys, transports and light ships each occupy 1 combat width. [1]

Engagement width has a base of 5.[2] It increases over time as diplomatic technology improves.

Diplomatic technology.png Diplomatic technology level 2 7 12 18 22 24
Engagement width.png Engagement width +20 +10 +15 +10 +5 +10
Totals (Cumulative) 25 35 50 60 65 75

These base technology levels of combat width can be augmented by the following:

Global naval engagement.png Conditions
+20% with Ab more ships can fire.png “Naval Engagement” ability in the Age of Revolutions.png age of revolutions
+10% per pip of admiral's Naval leader maneuver.png maneuver skill
for being the naval hegemon
Global naval engagement.png Traditions Ideas Bonuses Policies
  • Piratical idea 4: Sail in Consort
  • Naval-Exploration: Skilled Cartographers
  • Naval idea 7: Superior Seamanship
  • Danish ambition
  • Naval-Espionage: The Maritime Intelligencer Unit

A flagship with Flagship Modification improved crows nest.png “Improved Crow's Nest” modification increases the fleet engagement width by 3.

In a coastal sea zone engagement width is reduced:[3]

Local naval engagement.png −20% Local naval engagement

Combat sequence

The conclusion to a naval engagement

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:

  1. Heavy ships
  2. Galleys
  3. Light ships
  4. Transports

Any ships already disengaged will be ignored.

Importantly, any ships in excess of the engagement width are placed in reserve (until they replace those destroyed or disengaged) where they suffer morale damage although not in the fight. Therefore be sure to rather time adding smaller fresh and high morale reinforcements during each phase of the battle than merely throwing one full stack at the enemy.


Combat is divided into a series of 3-day phases where the phases alternate between fire and shock, with the fire phase happening first. Therefore each 6 days (after a full cycle of fire and shock) it may be best to try and reinforce the engagement width line with fresh reinforcements as others have been lost or disengaged during these two phases. Staying in reserve in the backline causes severe morale reductions, even while not fighting. So timing reinforcements to match the phases is generally better than depending on ships in reserve.

Target selection

Targeting, and specifically combined targeting, is why the "cannon:hull strength" ratio together with the relative combat width is so important in determining the outcome of a naval battle.

In combat each ship in the front line (all ships up to the engagement width) 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 (hence heavies are more likely to target other heavies, and galleys to target other galleys)
  • x0.1 if morale at 0 or less
  • x2 if hull strength is less than 50% (hence their appeal is doubled, resulting in many ships focusing fire or "ganging up" on the same weaker targets)

The enemy ship with the highest score is selected as a target. If the previous target is about to die, a new one will be targeted. This group focus on the weaker ones below 50% to push them to zero is why a battle can so quickly turn; normally as one runs out of reinforcements or ships in reserve and those still remaining in the fight have their morale collapse en masse.

Note that unless a ship disengages it may remain in the combat width line-up at near zero value, inhibiting a fresher high-strength ship to replace it in the combat width. This makes increases in disengagement chances very valuable.

The successful outcome of this combined targeting can be enhanced by your maximizing the number of cannons to target (from sending in higher quality ships - whether heavies or galleys, and from having a disproportionately higher engagement width than the enemy) as Cannons/Target Hull is the key factor in both the Final Damage and Morale Loss calculations.

Die roll

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.

Hull damage

Base damage is calculated according to the following formula:

Base Hull Damage = 0.025 + 0.025 * (2 + Dice + Combat Modifiers); where Combat Modifiers include the Artillery Fire Modifier, Naval Doctrine Bonus (England) and Admiral pip value difference (between 0 to 6) for that phase of the battle. Ship Combat Ability and Admiral Combat Ability are modifiers applied in the Final Damage formula.

The amount of cannons of the attacking vessel affects the hull damage dealt and the hull strength (hull size) 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 (with reference not to its Diplomatic Tech, but rather to its Military Tech, and therefore to the relative difference between each side's artillery damage modifiers). For example, jumping from tech 21 to tech 22 relative to your enemy in fact means a cumulative artillery fire difference of +2 (+4.4 vs. +2.4), which doubles this modifier.

  • 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.

Importantly, note that since Ship Durability is the denominator (and therefore affecting all the factors), one can drastically reduce the damage taken by having any modifiers that increase durability. For example, the 5% from the Corvettes Idea under Quality.

Galleys fighting in the inland sea have their Final Damage doubled. Which means that in inland seas, instead of fighting 3 galleys, one heavy is effectively fighting 6. Hence it's best to match galleys to galleys in inland seas and try and maximise your engagement width using a high pip manoeuvre admiral. Having a naval reformer advisor to boost morale will help too.

Morale damage

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:

Morale hit when losing a ship.png Traditions Ideas Bonuses Policies
  • Naval idea 3: Naval Cadets
  • Portuguese idea 1: Legacy of the Navigator
  • Humanist-Maritime: The Citrus Statute
  • Betsimisaraka traditions
  • Galician idea 6: Sailors of the Cantabrian Sea
  • Naxian idea 2: Naxos Rules The Waves
  • Catalan ambition
  • Naval-Religious: Zealous Captains
Morale hit when losing a ship.png Conditions
+10% Admiral with Level-headed personality


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.

Ship disengagement chance.png Traditions Ideas Bonuses Policies
  • Australian idea 5: Royal Australian Navy
  • Danish idea 3: Old Naval Traditions
  • Portuguese idea 1: Legacy of the Navigator

Combat statistics

Diplomatic technology.png Cumulative diplomacy technology effects to navy

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

Military technology.png Cumulative military technology effects to navy

Mil Tech Level 0 7 13 16 22 25 32
Artillery Fire +0.0 +1.0 +1.4 +2.4 +4.4 +6.4 +8.4

note : ONLY the Artillery Fire difference between attacker and defender is calculated, not the total, so the +1 of Spain and Aragon mean they have ALWAYS an impact (5% hull damage) if on time in naval tech.

Max naval morale

The following contributes to the maximum morale of a nation's navy.

Factor Amount
Naval maintenance 20% at minimum maintenance (minimum of 0)
100% at maximum maintenance (multiplicative modifier)
Navy tradition.png Navy tradition +25% at 100 navy tradition
Yearly prestige.png Prestige +10% at 100 Prestige, −10% at −100 prestige
Power projection.png Power projection +10% at 100 power projection
Advisor Naval reformer.png Naval reformer advisor +10%
Become Defender of the Faith.png Defender of the Faith +5%
Bankruptcy −50%
War exhaustion.png War exhaustion −2% per 1 war exhaustion

Certain National Ideas, Idea groups and policies will bump naval morale.

Morale of navies.png Traditions Ideas Bonuses Policies
  • Alaskan traditions
  • British traditions
  • Genoese idea 2: The Lessons of Chioggia
  • Kono idea 3: Oyamazumi Shrine
  • Norwegian idea 1: Natural Seamanship
  • So idea 3: Fight for Tsushima
  • Luzon ambition
  • Quality-Maritime: The Organized Marines Act
  • Omani traditions
  • Bregenzer idea 7: The Lake Constance Navy
  • Chiba idea 7: Naval Reform
  • Corsican idea 2: The Battle of Meloria
  • Madyas idea 2: Legacy of Panai
  • Manx idea 4: Mann and the Isles
  • Ouchi idea 3: Protect Against Piracy
  • Sicilian idea 6: The Grand Navy
  • Dalmatian ambition
  • Mogadishan ambition
  • Ragusan ambition
  • Siddi ambition
  • Candarid traditions
  • Naval idea 7: Superior Seamanship
  • Quality idea 5: Naval Drill
  • Danish idea 3: Old Naval Traditions
  • Piratical idea 5: Elected Quartermasters
  • Exploration-Defensive: The Naval Secrecy Act
  • Religious-Maritime: Chaplains of the Fleet

Each point of naval tradition also increases naval morale recovery by +0.10%.

Combat ability

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

Heavy ship combat ability.png Traditions Ideas Bonuses Policies
  • Naval idea 6: Oak Forests for Ships
  • British traditions
  • Butuan idea 6: Protect the Coastlines
  • Date idea 5: Red Seal Ships
  • English idea 1: A Royal Navy
  • Spanish idea 4: A Spanish Armada
  • Majapahit idea 6: The Majapahit Armada
  • Alaskan ambition
  • Genevan ambition
  • Innovative-Maritime: New Naval Tactics

Light ship combat ability improvement

Light ship combat ability.png Traditions Ideas Bonuses Policies
  • Veronese ambition
  • Alaskan traditions
  • Cham traditions
  • Ferraran traditions
  • Icelandic idea 4: Armed Merchants
  • Moluccan idea 6: Alliance with the Papuans
  • Arakanese ambition
  • Holstein ambition
  • Maritime-Plutocratic: The Protected Shipping Lanes Act
  • Hamburger traditions
  • Pattani traditions
  • Somali idea 6: Corsairs of the Red Sea
  • Sumatran idea 3: Spice Pirates

Galley combat ability improvement

Galley combat ability.png Traditions Ideas Bonuses Policies
  • Naval idea 2: Improved Rams
  • Venetian ambition
  • Aragonese traditions
  • Barbary Corsair traditions
  • Cebu traditions
  • Hosokawa traditions
  • Ionian traditions
  • Tunisian traditions
  • Berber idea 7: The Brothers Barbarossa
  • Cypriot idea 6: Repel the Corsairs
  • Italian (cU) idea 3: Mare Nostrum
  • Kitabatake idea 4: Kuki Suigin
  • Knights Hospitaller idea 4: Reconquista of the Sea
  • Moroccan idea 4: Defend the Coastline
  • Kono idea 5: Rule Over the Inland Sea
  • Maritime-Quantity: Streamlined Galley Production
  • Naxian idea 1: Maritime State
  • So idea 2: Wakou Tradition
Transport combat ability improvement
The combat ability of transports is not modified by the base game.

Unit pips

Main article: Naval units

Each ship has stats in three categories: Hull.png Hull, Icon ship cannons.png Cannon, and Icon ship speed.png Speed.

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. Therefore, the damage sustained by the hull is directly proportional to the number of cannons firing at it.

Leader pips

Leaders are rated on a scale of 0 to 6 for each of the following skills:

  • Naval leader fire.png Fire, Naval leader shock.png Shock

The leader's skill difference is added to the dice roll of its respective phases.

Naval leader fire.png Traditions Ideas Bonuses Policies
  • Dutch idea 4: Instructie voor de Admiraliteiten
  • Naval idea 3: Naval Cadets
  • Ferraran idea 7: The Ferraran Arsenal
  • Norman idea 7: Great Commanders
  • Tunisian idea 5: Board of Captains
  • Corsican ambition
  • Madyas ambition
  • Naval-Innovative: The Nautical Education Act
Naval leader shock.png Traditions Ideas Bonuses Policies
  • Naval idea 1: Boarding Parties
  • Madyas idea 4: Masters of Maritime Warfare
  • Naval-Religious: Zealous Captains
  • Naval leader maneuver.png Maneuver

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.

Naval leader maneuver.png Traditions Ideas Bonuses Policies
  • Madyas traditions
  • British idea 7: Britannia Rules the Waves
  • Mahri idea 4: Pilots of the Arabian Sea
  • Mogadishan idea 2: Somali sailors
  • Omani idea 6: Skilled Captains
  • Spanish idea 4: A Spanish Armada
  • Swahili idea 2: Monsoon Season
  • Innovative-Maritime: New Naval Tactics
  • Maritime-Offensive: Hold the Weather Gauge
The conclusion to a naval engagement

Concluding a battle

A naval battle ends when one side is either:

  • Reduced to 0 morale; or
  • Flees from combat; or
  • Annihilated (stack wiped)

Upon victory, ships from the defeated fleet may be captured, depending on your chance to "capture enemy ship" (during a battle, hover your cursor over this percentage in the top right of the battle popup). Your capture chance is affected by selecting "ship boarding" as your naval doctrine (providing you a 33% chance of capturing a ship), ideas such as the "reconquista of the sea" of The Knights (15% chance), policies from Naval&Diplomatic (33%), and the relative maneuver skill difference between the admirals of the two fleets. Generally very few or 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:

Chance to capture enemy ships.png Traditions Ideas Bonuses Policies
  • Naval-Diplomatic: Terms of Surrender Statute
  • Betsimisaraka idea 5: European Pirate Communities
  • Knights Hospitaller idea 4: Reconquista of the Sea
  • Cornish idea 4: Pirates of Penzance
  • Dithmarscher idea 4: Expert Wreckers
  • Kono idea 7: Murakami Suigun
  • Pattani idea 4: Lian Dao-Qian Band

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.

Morale recovery

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.

Recover navy morale speed.png Traditions Ideas Bonuses Policies
  • Humanist-Naval: The Naval Inspection Act
  • Naval-Innovative: The Nautical Education Act
  • Religious-Maritime: Chaplains of the Fleet

Each point of naval tradition also increases naval morale recovery by +0.1%.

Unit strength

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 of 100% strength in inland seas[4] and a bonus of 50% strength in coastal sea tiles which are not in inland seas[5]. The inland seas are shown below in pale blue.

Terrain map.

Ship repair

Fleets that have sustained damage will automatically repair up to their full strength when docked in an owned, allied, or in a province with fleet basing rights. There is a 'repair damaged' button that will detach damaged ships and send them to a nearby port to repair, when they are back up to full strength they will rejoin the fleet.

Main article: Navy#Ship_Repair

Naval doctrine

A country that has a Naval forcelimit.png naval force limit of at least 20 may select a naval doctrine. Selecting a naval doctrine, or changing to a different one (which can be done at any time), costs Gold Icon.png 0.1 ducat per Sailors.png sailor cost of the country's navy (i.e. Gold Icon.png 5 per light ship or transport, Gold Icon.png10 per galley, and Gold Icon.png20 per heavy ship).

The doctrines are:

Doctrine Effect Notes
Fleet In Being icon
Fleet In Being
Our naval influence shall be felt without the expense of our fleet leaving port except under the most favourable of conditions.
Naval maintenance modifier.png −15% Naval maintenance modifier
Free Oarsmen icon
Free Oarsmen
We shall fight the temptation to have slaves and the condemned rowing our Galleys. Free men, resilient in the face of adversity and resistant to defection shall form the muscle of our navy.
Galley combat ability.png +15% Galley combat ability
Merchant Navy icon
Merchant Navy
Our fleet's prime directive is to serve the financial interests of the State. Every effort shall be made to ensure our cargo ships are laden with foreign riches.
Ship trade power.png +33% Ship trade power
Ship Boarding icon
Ship Boarding
With established Prize Law and generous Letters of Marque we will nurture a custom of seizing enemy ships intact.
Chance to capture enemy ships.png +33% Chance to capture enemy ships
Wooden Wall icon
Wooden Wall
In a world of rapid change the seas remain of crucial importance to our nation. Both as means to secure our dominance and as the first line of defense our wooden wall shall prevail.
Naval combat bonus off owned coast.png +1 Naval combat bonus off owned coasts Requires Culture icon.png British culture group
Grand Armada icon
Grand Armada
A grand convoy shall accompany the treasure fleets that bring the wealth of the Americas into our home ports.
Treasure fleet income +50% Treasure fleet income Requires Culture icon.png Iberian culture group, but not Portuguese or Brazilian
Portuguese Marines icon
Portuguese Marines
To establish a truly global empire we must be skilled at launching assaults on enemy forts from the sea.

Marines force limit.png +10% Marines force limit

Requires Culture icon.png Portuguese or Brazilian culture

Fleet actions

Start patrolling

Start patrolling button.png The start patrolling button orders a fleet to loop its current movement order: when it reaches the final destination of its current set of movement orders, it will automatically head back to the point where the patrol was started. Patrol routes can include port visits, where the patrol stops until all ships are repaired. While the same function can be fulfilled by light ships assigned to protecting trade nearby, patrols are not limited by ship type, trade power, or trade range.

Coastal Raiding

Costal Raiding is a naval ability added in the Mare Nostrum expansion which allows fleets belonging to nations with the Raid Coasts idea, which in the base game belongs to the Maghrebi culture group (Flag of Morocco Morocco, Flag of Tlemcen Tlemcen, Flag of Tunis Tunis and the formable nations of Flag of Algiers Algiers and Flag of Tripoli Tripoli), Flag of Habsan Habsan and Flag of The Knights The Knights to raid the coasts of other nations of a different religion for Gold Icon.pngloot (ducats) and Sailors.pngsailors. This idea is also available to Custom Nations.

The Golden Century.pngGolden Century DLC introduces Pirate Republics (specifically; Flag of New Providence New Providence, Flag of Tortuga Tortuga, Flag of Port Royal Port Royal, Flag of So So, Flag of Palembang Palembang (through an event) and Custom Nations with the Pirate Republic government), which also have the ability to raid coasts and are capable of raiding the coasts of countries with the same religion.

Historically, this ability reflects the raids carried out by Barbary pirates which were active in the Mediterranean Sea during the mid-16th to early 19th centuries while in the case of the three Pirate Republics, it simulates the Golden Age of Piracy in the Caribbean Sea from the mid-16th to the early 18th century. Flag of So So is a special case, as it represents a resurgence of the Japanese Wokou Pirates that raided the coasts of East Asia intermittently from the 4th century to the 17th century.

Raiding can provide a significant early-game boost to the income and sailor pools of nations that can do it and can also serve as a way to damage the economy of other nations. An example of this is Flag of So So, which can employ Coastal Raiding against Flag of Ming Ming to pile up devastation and cause Ming to potentially lose the Mandate of Heaven and collapse.


Raiding coasts as Morocco.

Raiding a coast is something fleets can do at sea. To raid a coastal province, the following needs to be true:

  • the nation…
  • the target province…
  • …must be no more than three sea tiles away from a province owned by the nation (cored or otherwise)
  • …must have a development lower than or equal to the blockading power of the fleet
  • …does not have the religion of the raiding nation, unless the raiding nation is a Pirate Republic
  • …does not belong to an ally or subject of the raiding nation
  • …does not have the “Raided Coast” modifier

After a province has been raided, its loot bar is emptied, the amount of devastation is increased, and the modifier “Raided Coast” is applied for ten years. Each raided province will add a −25 relations penalty with the target country (up to a maximum of −100), decaying by +1 per year.

The efficiency of raiding is reduced by fleets on pirate hunting patrol.

When a coast is raided, the loot provided is as follows:

Raided coast Conditions
  • +1 Income.png
per development (raided province)
+ sailors
Local sailors per Raided provinces / 4


Fleets will automatically blockade a coastal sea province under hostile control while they are stationary and have no other orders.

Blockade power

The blockade power (sail speed in the tooltip) of a fleet is displayed after the Blockade enemy ports.png blockade icon in the fleet panel. It is mainly determined by the Icon ship speed.png tactical movement speed of the fleet's ships.

Each point of blockade power will be able to blockade one development point of a province.

Ship type Tactical speed Blockade power
Heavy ship.png Heavy ships 5 5
Light ship.png Light ships 10 10
Galley.png Galleys 8 8
Transport.png Transports 5 5

Blockades will only take effect if there is enough blockade power to match the full development. If a fleet does not have enough blockade power to blockade all adjacent provinces under hostile control, it will assign its blockade power in precedence of:

  • Hostile province under a siege lead by any friendly force
  • Hostile province with the lowest development
  • Hostile rebel province with the lowest development

The detach blockade button (Detach blockade.png) in the fleet panel will detach a fleet of sufficient size to blockade all enemy ports neighboring the sea province.

Blockade efficiency

Blockade efficiency is determined by:

Blockade efficiency.png Conditions
+1% for every point of Navy tradition.png navy tradition

Ideas and policies:

Blockade efficiency.png Traditions Ideas Bonuses Policies
  • Maritime idea 7: Naval Fighting Instruction
  • Naval-Maritime: The Naval Supremacy Act
  • British idea 7: Britannia Rules the Waves
  • Omani ambition

Decisions and events:

Blockade efficiency.png Event modifier Trigger Duration
+20% Improved Blockade Tactics Maritime ideas event: Improved Blockade Tactics for 10 years.
−25% Blockade Standards Slipping Maritime ideas event: Slipping Standards
Option: ‘Well we can't expect them to operate at peak efficiency all the time’
for 10 years.
Blockade force required

Blockade force required is determined by:

Blockade force required.png Conditions
+50% Coastal defence.png Coastal defence
+100% Naval battery.png Naval battery

Effects of blockade

A blockade has a number of effects on any neighbouring land provinces occupied by an enemy:

Local recruitment time.png +20% Local recruitment time
Local shipbuilding time.png +20% Local shipbuilding time
Local devastation +0.1 Monthly devastation

Notably, provinces producing Spices.png Spices get negative monthly devastation that exactly counteracts the positive modifier from blockades.

Blockading a country's ports also applies the following modifier, scaled by proportion of (core, state) development blockaded:

Monthly war exhaustion.png +0.10 Monthly war exhaustion

Blockades have the following further effects:

  • Siege: −2 penalty to die rolls in non-blockaded coastal provinces, except those owned by primitives. (Provinces without ports, e.g. on the Caspian Sea, don't count.)
  • War score: Blockades are worth war score scaling with the proportion of development they represent and local autonomy. Capital and fortified provinces are worth more. Some casus belli have blockades as a war goal.
  • Spoils of War: Blockades add Gold Icon.png ducats to the blockader's treasury (listed under "Spoils of War") in proportion to the province's income.
  • Restriction of movement: See § Blocking a strait below.

Blocking a strait

To block a strait the following requirements must be met:

  • The blockading alliance or a neutral nation have to control (owns or occupied) at least one side of the adjacent provinces
  • The blockading alliance have to control the sea by a naval force (blockade efficiency doesn't matter)

As a consequence, if a war alliance controls both sides of the strait they can march over regardless of blockades.


  • A war participant controlling both sides of a strait: The Ottomans can cross the strait at Bosphorus as long as they have control of Constantinople and Kocaeli even when the enemy controls the sea. Same system applies for the second strait between Gelibolu and Biga.
  • A neutral nation controlling a side of a strait: Ulster, controlling Ulaidh, cannot cross the strait across the Irish Sea to Ayrshire in Scotland if Ulster is only at war with England (Scotland is neutral and gives military access to one of the war participants), and England controls the Irish Sea.
  • However, if Ulster has called in an ally, say Burgundy, and Burgundy is in a separate war with Scotland and controls Ayrshire, then the first requirement is no longer fulfilled, and the Irish nation can cross the strait despite England having control of the Irish Sea.

Besieging a province of a strait does not fulfil the first requirement; the siege must finish, translating to control.

Naval missions

Fleet missions are grouped together under a collective “Select Mission” button (Select mission.png) that allows the player to tell their fleets to;

  • Protect Trade
  • Privateer
  • Hunt Pirates
  • Explore
  • Hunt Enemy Fleets
  • Blockade Enemy Ports
  • Intercept enemy fleets

Protect trade

Protect trade.png

This mission is available to any fleet that contains light ships. It will add the trade power of the light ships in the fleet to any maritime trade node that the player already has some trade power in, provided that the trade node is within both trade range and supply range.

The trade power of light ships depends on ship model, and increases as diplomatic technology advances. Furthermore, it scales linearly with the naval maintenance slider, reaching full potential at maximum naval maintenance, but suffering a −75% penalty at minimum naval maintenance. AI nations do not suffer a trade power penalty to light ships from low naval maintenance.



This mission is available to any fleet that contains light ships. The fleet will hoist the Jolly Roger and add the trade power of its light ships to a pirate nation in any selected trade node. Unlike the protect trade mission, existing trade power is not needed in a trade node to start a privateer mission.

Privateer efficiency

Light ships on privateer missions receive a +50% bonus to their trade power. Privateers do not inherit any national bonuses or penalties to global trade power. Factors such as overextension or halved trade power when collecting in foreign nodes are notably ignored. The trade power of privateers is instead affected by various privateer efficiency modifiers:

Privateer efficiency.png Traditions Ideas Bonuses Policies
  • Naval-Maritime: The Naval Supremacy Act
  • Offensive-Exploration: Letters of Marque
  • Espionage idea 6: Privateers
  • Maritime idea 7: Naval Fighting Instruction
  • Cebu idea 5: 'The Place for Trading'
  • Mindanao idea 7: Pirates of Mindanao
  • Naxian idea 3: Archipelago Of Opportunities
  • Barbary Corsair traditions
  • Cornish idea 4: Pirates of Penzance
  • Dithmarscher idea 4: Expert Wreckers
  • Kono idea 7: Murakami Suigun
  • So idea 4: Bahan Ship
  • East Frisian traditions
  • Gutnish traditions
  • Al-Haasa idea 7: Legacy of Rahmah ibn Jabir
  • Arakanese idea 4: Magh and Ferenghi
  • Betsimisaraka idea 2: Pirate Ports
  • Cypriot idea 7: Raid Turkish Commerce
  • Malagasy idea 3: Pirate Ports
  • Montenegrin idea 4: Balkan Gusars
  • Moroccan idea 5: Protect Pirate Republics
  • Munster idea 6: Pirate Haven
  • Norman idea 5: Viking Raids
  • Novgorod idea 6: Funding the Ushkuiniks
  • Pattani idea 4: Lian Dao-Qian Band
  • Pomeranian idea 1: Legacy of Pirates
  • Sumatran idea 3: Spice Pirates
  • Berber idea 4: Corsairs
  • Sonoran idea 5: Taking What’s Ours
  • Tunisian idea 3: Corsairs

The trade power of ships assigned to the privateer mission affect the trade power they have in the node, this means that the flagship +1 trade power per ship modification and the +33% ship trade power merchant navy naval doctrine, as well as other ship trade power modifiers affect privateers.

The Enlist Privateers decision increases Privateer efficiency.png privateer efficiency by another +25%. It becomes available at 8 Diplomatic technology.png Diplomatic technology and requires the nation to have completed Maritime idea group.png Maritime ideas, a ruler with 3 Military power.png Military, as well as 50% of the Naval forcelimit.png force limit.

With Common Sense.png Common Sense, winning a Parliament.png parliament debate "Issue Letters of Marque" provides +15% privater efficiency for 10 years.

Each point of naval tradition also increases privateer efficiency by 0.25%. The total trade power from privateers is thus

privateer trade power = Ship trade power.png trade power from light ships × 1.5 × (1 + naval maintenance modifier) × (1 + Privateer efficiency.png privateer efficiency)

Note that without Wealth of Nations.pngWealth of Nations, El Dorado.pngEl Dorado, Mare Nostrum.pngMare Nostrum or Golden Century.pngGolden Century DLC enabled the modifiers are exchanged. Privateer efficiency is replaced by trade power abroad.


Privateer fleets can only reach trade nodes in sea zones that are within trade range. A nation's trade range extends from cored provinces of the nation or its subjects, as well as coastal ports of any nation that has granted it fleet basing rights.

Trade range can be increased by diplomatic technology, decisions, ideas, and policies:

Trade range.png Traditions Ideas Bonuses Policies
  • Ryukyuan idea 4: Maritime Commercialism
  • Swahili traditions
  • Trade idea 3: Merchant Adventures
  • Ayutthayan idea 5: Promotion of Trading links
  • Gujarati Princedom idea 7: Extend Trade Routes to Africa
  • Gujarat Sultanate idea 2: Jain Connections
  • Kono idea 6: Trade With Continental Asia
  • Malabari idea 1: Merchants of Southern India
  • Mesoamerican idea 7: Obsidian and Jade
  • Mogadishan idea 1: Indian Ocean Trade
  • South Indian idea 1: Merchants of Southern India
  • Traditions of The Hansa
  • Sumatran traditions
  • Evenk idea 2: Reindeer Herding
  • Dutch idea 2: Dutch Trading Spirit
  • Mamluk idea 1: Red Sea Trade
  • West Indies idea 4: The American Trade Hub


The privateer fleet increases the trade power of a pirate nation that acts as a collector in the trade node. This pirate nation will submit 40% of its earnings to the nations that commissioned the privateers contributing to its trade power. The presence of this pirate nation effectively reduces the share of trade value controlled by all non-pirate nations in the node. Income from privateering will be recorded in the economy window as spoils of war.

Any country that would have more than 20% of the trade power in the node without privateers will receive a casus belli against any nation that has sent privateers to that node.

Any country that would have more than 10% of the trade power in the node without privateers will have a −1 opinion modifier per month of any nation that has sent privateers to that node, capped at −100.

Sending light ships on privateer missions against rivals is one of the easiest ways to acquire power projection. This can be especially useful to increase the power projection of the player beyond +25 for +1 free leader, or beyond +50 for +1Administrative power.png / +1Diplomatic power.png / +1Military power.png each month.

Activating a privateer mission will force the game to update a nation's power projection on the next game day. This will consequently update, among other things, the trade power in trade nodes and the nation's military force limits. Triggering an update like this can be useful when game stats are temporarily desynchronized due to certain actions, such as sending light ships to protect trade or changing local autonomy levels.)

Hunt pirates

Hunt pirates.png

This mission is available to fleets which contain at least one ship that isn't a transport. Fleets containing Heavy ship.png heavy ships or Light ship.png light ships may hunt pirates in any trade node which is not Inland node.png inland; however, fleets containing only Galley.png galleys (as well as fleets which are a mixture of galleys and transports) can only hunt pirates in nodes where all nearby sea provinces are inland seas, e.g. in Basra and Alexandria, but not in Hormuz. This does not necessarily mean that fleets will only hunt in inland sea provinces (where they are more effective): for instance, a fleet hunting pirates in Canton will use the Luzon Strait.

The total Icon ship cannons.png number of guns of the ships is used to find the efficiency at which they hunt the pirates. The Trade power.png trade power of pirates is reduced by hunt pirate efficiency. 0%, when no fleet is hunting pirates, up to 99%, if the total number of guns from the hunting fleet is greater than or equal twice the total number of guns from pirating fleet.

In addition, it is helpful to know that this is also effective at stopping other nations from raiding your coasts.

Note that pirate fleets and fleets hunting pirates do not actually battle or otherwise damage each other, unless the countries that own the fleets are at war with one another.


Main article: Colonization#Discovery

This mission requires an explorer, and a total of 3 light and/or heavy ships. It sends the fleet to explore a region or a coast line, that can be chosen by either selection the region on the UI or clicking on the naval TI with the "explore" tab opened, and the player can attempt to circumnavigate the globe at diplomatic technology 9.

Hunt enemy fleet

Hunt enemy fleet.png

The fleet will hunt enemy fleets in a specific sea region, that can be chosen by either selecting the region in the UI or clicking on the naval region with the tab opened.

Blockade enemy ports

Main article: Naval warfare#Blockading
Blockade enemy ports.png

The fleet will blockade enemy ports and evade enemy fleets that are not significantly weaker. (Can be altered by setting the fleet to be Bold.)

Intercept enemy fleets

Intercept enemy fleets.png

This mission will have the fleet seek out enemy fleets near allied coastlines, focusing on troop transports.

Strategies and tactics

Strategy The below is one of many player suggested strategies for Naval warfare. Bear in mind, due to the dynamic nature of the game, it may unfold differently for other players.


Decisive wins can be achieved in battle by concentrating all battle ships (heavies and galleys) in one fleet up to just a little over the engagement width, with a re-enforcement fleet in the neighbouring tile. Seek battle if one has superior naval assets, and avoid engagement otherwise.

When ready to attack detach and send only the front line (your best ships and flagship up to the value of your engagement width and a few more) into battle. Then as the phases progress feed reinforcements every few days from your neighbouring reinforcing fleet piece-meal into the battle to replace destroyed or disengaged ships. This will reduce morale losses from having as few ships as possible in the reserve line in the battle. One could call it the "just-in-time" re-enforcement method.

Remember to maximise your engagement width by using your highest manoeuvre admiral, preferably with high shock and fire pips too. You want more ships than the enemy to all be firing at the same time.

Naval admirals can significantly tilt a battle in one's favor, even more so than generals; without an admiral, stack wiping and sometimes even victory becomes unlikely even with a seemingly overwhelming advantage.

However, other factors may complicate this. A country may be forced to divide their fleet if they have naval objectives other than destruction or suppression of the enemy navy, such as protecting (multiple) trade nodes, transporting land units by sea, exploring, patrolling for pirates, reconnaissance, blockading and so forth. If the country lacks naval supremacy compared to their enemies, they may be forced to risk losses, support fewer of these objectives at the same time, or leave the sea entirely for the duration of the war.

However, even if you are weaker than the enemy, tactics may make the difference in a long drawn out war. Smartly engage one enemy stack at a time (using the techniques above) whenever the odds are materially in your favour to win that specific battle. A sequence of such victories can quickly add up to war score and help ensure the enemy cannot land their troops.

Be sure to sail your full stacks into ports where you have coastal forts with terrain penalties for the besiegers. The enemy will be lured into sieging these unfriendly forts if they don't see your stacks nearby, while having fleets allow you to sail into these coastal forts before they can withdraw. Such attacks can lead to quick stack wipes of the enemy and can dramatically turn the war in your favour.

Bringing an enemy fleet to battle

A country with a naval advantage may wish to bring a reluctant enemy fleet to battle. This can be accomplished in several ways:

  • If the enemy fleet is docked at a port, they cannot be attacked directly. However, the fleet may be ejected by occupying (successfully sieging) that province, at which point the leaving fleet will enter into combat with any opposing fleet(s) in the corresponding sea province.
  • A small "bait" fleet may be used to lure the enemy into attacking, whereupon the main fleet can reinforce from a nearby sea province or port. This can also be used to lure fleets into or out of inland seas, where galleys have a relative advantage.
  • Light ships move faster than heavy ships / transports, which move faster than galleys. A fleet without galleys can easily catch an enemy fleet that contains galleys.
  • Putting your ships into port will usually cause the AI navy to be more aggressive and leave port, sometimes even attempting a full blockade, leaving their navy significantly more vulnerable.
  • After a defeat, an enemy navy will typically retreat to an adjacent port. Having an army already sieging down this port will give you a significant advantage, as the ships will be forced to leave port soon after arriving while having low morale and no repairs, allowing for a stackwipe or a victory in which they may lose most of their ships.
  • Sometimes a bug will allow the AI to remain permanently in a province even if it is sieged down. The only way to fix this is to retreat several sea tiles from the province and then go into port, or in other words give the ai an illusion of safety.


  2. See in /Europa Universalis IV/common/defines.lua: NAVAL_BASE_ENGAGEMENT_WIDTH.
  3. See in /Europa Universalis IV/common/static_modifiers/00_static_modifiers.txt (Static modifiers#Coastal sea).
  4. See in /Europa Universalis IV/common/defines.lua: GALLEY_BONUS_INLAND_SEA
  5. See in /Europa Universalis IV/common/defines.lua: GALLEY_BONUS_COASTAL_SEA

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