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

In Imperator there are six different types of naval unit.

	Unit type			Monthly	Requirements	Category	Maneuver	Naval movement speed
	Liburnian	5	120	0.08	Free	Light	4	13		−15%	−25%	−35%	−40%	−50%
	Trireme	8	180	0.13	Free	Light	3	12	+15%		−10%	−10%	−20%	−20%
	Tetrere	10	180	0.16	Wood	Medium	2	12	+25%	+10%			−10%	−10%
	Hexere	15	180	0.24	Wood	Medium	1	11	+35%	+10%	+5%		−10%	−10%
	Octere	25	180	0.41	Wood, Military tradition	Heavy	0	9	+40%	+20%	+10%	+10%		−10%
	Mega-Polyreme	32	365	0.53	Wood, Military tradition	Heavy	0	7	+50%	+30%	+20%	+20%	+10%

The fleet

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 (with fully reinforced cohorts 1000 men). Fleets can also blockade ports in wartime, decreasing commerce and potentially contributing to the warscore for their side of the conflict. Futhermore fleets in a sea zone with a strait will block enemy units from crossing that strait.

Building a fleet

Ships can only be built in ports, which only exist in predefined locations around the map. Building ships other than Liburnians and Triremes also requires access to wood in the province that the city belongs to.

Combat

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

• Strength damage is higher than with land combat so ships 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

Unit abilities

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).

Mechanics