Naval 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 and conquest.

Naval units

Basic stats

All ships have the same basic stats:

• The strength of a ship represents how intact it is, ranging from 100% to 0%. If a ship reaches 0% strength, it will be destroyed. Fleets do not reinforce but can instead repair in friendly ports at a rate of +10% strength per month. If the fleet has a (positive) Monthly Repair at Sea modifier, it can also regain strength while at sea (at the rate of 1% per 0.01 points of the modifier).
• All ships have a base of 3 morale, adjusted by the Morale of Navies modifier (as well as by the ship type-specific morale modifiers). This determines how much morale damage the ship can take in battle before it retreats.
• Each ship has a certain amount of experience from 0% to 100%, which reduces damage in combat and can be gained from fighting and starting experience from buildings and other sources of the Starting Experience and Ship Starting Experience modifiers. Note that unlike army experience, naval experience does not count towards military experience gain (nor is there a naval equivalent).

Ship types

There are six different types of naval units, ranging from light to heavy:

	Unit type			Monthly	Port level	Requirements	Category	Maneuver	Naval movement speed	Morale damage done	Morale damage taken	Strength damage done	Strength damage taken
	Liburnian	5	120	0.08	1	None	Light	4	13	+15%
	Trireme	8	180	0.13	1	None	Light	3	12		-10%
	Tetrere	10	180	0.16	3	Wood	Medium	2	12
	Hexere	15	180	0.24	3	Wood	Medium	1	11		-10%	+10%
	Octere	25	180	0.41	5	Wood, Military tradition	Heavy	0	9		-10%		-10%
	Mega-Polyreme	32	365	0.53	5	Wood, Military tradition	Heavy	0	7		-30%	+40%	-30%

The meaning of each column is described below:

• - The base recruit cost of the ship type. Modified by the country's Ship Building Cost modifier.
• - The base recruit time of the ship type. Modified by the country and territory's Ship Recruit Speed modifier.
• Monthly - The base monthly maintenance of the ship type. The maintenance is calculated as 1/60 of the ship's recruit cost, so it is modified by both the Ship Building Cost and Navy Maintenance Cost modifiers.
• Port level - The minimum port level required to recruit this ship type.
• Requirements - Any additional requirements to recruit this ship type.
• Category - The overall class of the ship type. Some unit actions are restricted to certain ship types.
• Maneuver - The ship type's (horizontal) range when selecting an enemy ship to attack while in combat
• Naval movement speed - The ship type's movement speed. Lighter ships are faster, but a fleet will always move at the speed of its slowest ship. Modified by the Naval Movement Speed modifier.
• Morale damage done - Base ship type modifier to Morale Damage Done, which modifies the amount of damage to enemy ship morale the ship type does in combat
• Morale damage taken - Base ship type modifier to Morale Damage Taken, which modifies the amount of damage to morale the ship type takes in combat
• Strength damage done - Base ship type modifier to Strength Damage Done, which modifies the amount of damage to enemy ship strength the ship type does in combat
• Strength damage taken - Base ship type modifier to Strength Damage Taken, which modifies the amount of damage to strength the ship type takes in combat

Most to all of these modifiers have versions that apply to all ships, as well as versions that only apply to one particular ship type.

Unit type combat effectiveness

The effectiveness of each ship type against each other ship type can be seen below (rows attacking vs. columns defending). In general, lighter ships perform poorly against heavier ships.

	Unit type
	Liburnian		−15%	−25%	−35%	−40%	−50%
	Trireme	+15%		−10%	−10%	−20%	−20%
	Tetrere	+25%	+10%			−10%	−10%
	Hexere	+35%	+10%	+5%		−10%	−10%
	Octere	+40%	+20%	+10%	+10%		−10%
	Mega-Polyreme	+50%	+30%	+20%	+20%	+10%

Recruitment

Ships are built, or recruited, individually in owned and controlled port territories (through either the macrobuildier or the Build Ships button in the Tactical tab). Each ship type has a certain upfront gold cost and takes a certain amount of time to build, adjusted by the Ship Cost and the Ship Recruit Speed modifiers, respectively. Heavier ships cost more and take longer to recruit. Each port territory can only build one ship at a time (regardless of how many ports it has, though each port will increase the ship recruit speed). Once built, the ship will appear in the port it was built in at full strength and morale and experience equivalent to the sum of the Starting Experience and Ship Starting Experience modifiers, and either automatically join one of the fleets already docked at the port or create its own fleet if there are none already there. If the ship was built using the Build to Navy action, it will attempt to join the navy it was ordered to be built to.

Only light ships ( Liburnians and Triremes) can be built by all countries at the start of the game. All medium and heavy ships require that the territory's province have at least 1 wood (either locally produced or imported), while heavy ships must be unlocked by taking certain military traditions. Octeres are unlocked in the Greek, Levantine, Indian, and Persian tradition groups, while Mega-Polyremes can only be unlocked through the Greek and Levantine tradition groups.

Attrition

Ships suffer attrition when outside of the country's naval range. Attrition damages ships over time and can eventually lead to the destruction of an entire fleet.

Fleets

The main purpose of a fleet is to ferry troops from one destination to another, and to stop others from doing the same in your territorial waters. One ship can transport one cohort (one fully reinforced cohort consists of 500 men). Fleets can also blockade ports in wartime, decreasing commerce and potentially contributing to the warscore for their side of the conflict. Also, fleets in a sea zone with a strait will block enemy units from crossing that strait.

Fleet commander

Main article: Admiral

Every fleet can have an commander, or admiral, that leads the fleet in battle, analogously to the commanders of armies. Like with army commanders, the higher the martial skill of an admiral, the more effective he or she will be in leading the fleet in battle.

Transporting armies

An army can embark on owned fleets to be transported across seas or major rivers, with naval transport generally being much faster than marching across land. Each ship can carry one cohort, regardless of the type of ship and/or cohort. Embarking and disembarking is instantaneous if the fleet is docked at a (friendly) port, but armies can also embark or disembark directly from sea tiles to neighbouring land territories (though this takes much longer).

Pirate fleets

Main articles: Mercenaries, Pirates

Pirate havens host pirate fleets which can be hired as naval mercenaries to supplement a country's navy. Pirate fleets always consist only of light ships and, when not being hired, may become hostile and attempt to raid nearby ports. If destroyed they will eventually regenerate at their home port, and can be permanently destroyed by destroying their home pirate haven.

Combat

Combat is very similar to land warfare. The major differences are:

• Strength damage is higher than with land combat, so ships are more likely to sink in combat.
• Defeated ships have a chance to get captured.

Combat tactics

As with land combat, navies have combat tactics that give bonuses against specific other tactics. How effective a tactic is depends on the fleet's composition.

	Tactic	Unit effectiveness	Against other tactics	Description
	Frontal Assault	Liburnian: 50% Trireme: 100% Octere: 100% Mega-Polyreme: 200%	Harassment: +20% Close Ranks: −10%	Sometimes the most efficient approach is to have a strong center that breaks through the enemy line. By concentrating our strongest ships in such a way we can break apart an enemy fleet quickly.
	Naval Envelopment	Trireme: 100% Hexere: 100% Mega-Polyreme: 100%	Close Ranks: +20% Probing Attack: −10%	Envelopment is an old and tried tactic at sea just as it is on land. Loading one flank with stronger and more numerous ships can allow us to overcome the enemy's flank and expose their ships from a sideway attack.
	Close Ranks	Trireme: 50% Hexere: 100% Octere: 100% Mega-Polyreme: 100%	Frontal Assault: +20% Naval Envelopment: −10%	If all ships stay as close together as they can it will be harder for the enemy to perform ramming or boarding.
	Harassment	Liburnian: 100% Trireme: 100% Octere: 100%	Probing Attack: +20% Frontal Assault: −10%	An approach of constant harassment in an attempt to wear down the enemy fleet through frequent minor attacks.
	Probing Attack	Liburnian: 100% Tetrere: 100% Hexere: 100%	Naval Envelopment: +20% Harassment: −10%	Sometimes the most efficient approach is to have a strong center that breaks through the enemy line. By concentrating our strongest ships in such a way we can break apart an enemy fleet quickly.

Capturing

Ships have a chance to be captured when they are defeated. There are 3 different cases:

• Morale runs out: This is the normal scenario. The capture chance is based on ship categories and the enemy general.
• Strength runs out: Same thing as above. However the ship gets destroyed even if it gets captured (resulting in multiple losses in the after battle screen).
• Stack wipe: Result of enemy being greatly outnumbered or getting defeated very quickly. The capture chance from the ship category is replaced by a fixed chance. Any captured ships during combat from the stack wiped side are returned to their original owners.

Sources of capture chance (all sources stack additively):

Type	Amount	Description
Base	+6%	The global capture chance. Military window shows that the base chance is 5%. In-game tests resulted also in a hidden 1% base chance.
Stack wipe	+20%	Stack wiping doesn't involve combat so enemy ship category can't be used. In-game tests resulted in a 20% increased capture chance.
Capturing ship category	+10% per category	Capture chance is increased 10% for light ships, 20% for medium ships and 30% for heavy ships.
Captured ship category	−10% per category	Capture chance is decreased 10% against light ships, 20% against medium ships and 30% against heavy ships.
General martial	+0.2% * martial	Martial skill of the general slightly increases the capture chance. For example 10 Martial gives a 2% increased chance.
General trait Sea Dog	+10%	Sea Dog trait increases the capture chance.
Boarding Tactics	+10%	Selecting the Boarding Tactics ability increases capture chance at the cost of reduced damage.

Examples

• Light vs Light, with level 10 martial. 6% + 10% - 10% + 0.2% * 10 = 8% capture chance.
• Light vs Medium, with level 10 martial. 6% + 10% - 20% + 0.2% * 10 = -2% capture chance.
• Medium vs Heavy, with Boarding Tactics. 6% + 20% - 30% + 10% = 6% capture chance.
• Heavy vs Heavy, with stack wipe. 6% + 20% - 30% = -4% capture chance.
• Light vs Heavy, with stack wipe and Boarding Tactics. 6% + 20% - 30% + 10% = 6% capture chance

Blockades

Fleets can blockade neighbouring ports that are controlled by hostile countries. Blockades increase a country's warscore and can loot a small amount of gold each month.

Navy actions

There are unit abilities for ships at sea:

• Ramming Tactics: Naval damage done +10%, Naval damage taken +10%
• Boarding Tactics: Naval damage done -10%, Naval capture chance +10%
• Raid Port: Steals a number of pops from an adjacent port and turns them into Slaves in your capital (at a cost of 1 Aggressive Expansion).

Unit objectives

Like with armies, player-controlled navies can be automated by assigning unit objectives.

Non-military implications

While ships are more politically neutral than cohorts in Imperator, admirals still gain power base based on the number of ships commanded. The substantial salary drawn by admirals also contribute to their family's prestige.

Mechanics