Space warfare

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This article is for the PC version of Stellaris only.

War

Warfare

Space warfare

Land warfare

Most warfare is settled through space combat. Though ground warfare is necessary to achieve ultimate victory, landing armies is safer once the fleet has eliminated the threat of enemy vessels intercepting and destroying vulnerable troop transports. Winning battles across the stars is about adapting to the enemy's loadout and using effective counters. Each offensive or defensive component has a counter-measure to it, meaning that component choices are likely to evolve and change as empires encounter new enemies and try to build ships that counter those of the opponent.

Combat[]

Space Battle — Space battle between mammalians and pirates

Combat in Stellaris takes place in real-time, out of the player's control save for the emergency FTL order. Though the player can direct a fleet toward or away from enemies, there is no control over individual ships (unless they make up a fleet on their own) or which ships they target.

Each fleet is shown on the screen with a strength number. This number represents the power of this fleet, measured by the combined offensive strength of all of the ships in the fleet. This is a rough guide to a fleet's prowess, but cannot be understood as an absolute determinant in how combat will play out. A fleet that has a lot of offensive weapons that are unsuited for the enemy it is facing (Alien entities with regenerating hulls or skins, enemies with sophisticated and appropriate countermeasures) may still lose to this enemy even though its strength number is considerably higher.

When a fleet engages an enemy ship, enemy station or alien creature in combat, the player gets an alert and the fleet listing in the Outliner has a red battle icon beside it. Select this fleet and you will see a real-time report of the ongoing combat.

At the top of the results sub-screen is a bar measuring the approximate strength of the opposing sides in combat. This bar changes as combat progresses and the odds shift in favor of one or the other side. As the battle progresses, the report sub-screen shows breakdowns of the effectiveness of the weapons systems in use and how much damage the shields, armor and hulls have taken. Analyzing this data helps determine whether current ship builds are effective against this opponent and may indicate ways to improve.

When in combat, every military ship will advance to within a certain range of its intended target and fire its weapons; combat computers determine what range the ship will engage its target from when in combat. Ships that have similar combat computers tend to cluster together, stay in formation with each other and attack in groups.

Damage[]

Damage by space combat is distributed onto three components: Hull Points, Armor, and Shields. Different weapons do different amounts of damage to each.

Hull Points is the most important attribute for any ship. When Hull Points reach 0, the ship will be destroyed. Furthermore, ships will have their fire rate decreased by a percentage equal to half of the percentage of Hull Points lost. Hull Points are determined by ship size and tech bonuses.
Armor provides an anti-kinetic layer of protection, based on the type of Armor component added, and tech bonuses.
Shields provides an anti-energy layer of protection, based on the type of Shield component added, and tech bonuses. Shields require energy from the ship's reactor and always regenerate, unlike Hull Points and Armor.

When being attacked, Shields will absorb damage first. After Shields are depleted, Armor will be damaged. After Armor is depleted, Hull Points will be damaged. Some weapons are better, or worse, than others at depleting Shields and/or Armor, and some weapons deplete Hull Points directly.

When the Hull, and Armor, are damaged the most common way to repair them is by docking the fleet with a Starbase. It is possible to repair ships other than by docking, such as a ship having the 'regenerative hull tissue' component, or a fleet's commanding Admiral having the 'engineer' trait. However, self-repairing is slower than dock-repairing (2% per day or 60% per month). Defense Platforms have a base self-repairing rate of 2% per day. It takes 30 days before a Starbase starts to repair itself after combat and there not being any hostile warships in the system. Disabled Starbases reactivate after 6 ticks of regen (36 days).

Ship protection modifiers are sparse, only two for each defense layer existing:

Source	Hull bonus
Unyielding Commander trait	+20%
Devouring Swarm civic	+25%

Source	Armor bonus
Volatile Reactive Armor edict	+25%
Matter Compression repeatable technology	+5%

Source	Shield bonus
Exotic Gases for Shield Boost edict	+25%
Shield Harmonics repeatable technology	+5%

Accuracy, Tracking, Evasion[]

Three parameters determine the chance of a weapon to hit its target: the accuracy and tracking of the attacker, and the evasion of the defender.

Accuracy comes primarily from the weapon stats. Accuracy is the percentage chance to hit a target with no evasion. Weapons with high accuracy tend to have comparatively low damage or other weaknesses. Accuracy is capped at 100.

Tracking comes primarily from the weapon stats as well. Tracking will cancel out some or all of the defender's evasion, and the actual chance to hit is the attacker's accuracy minus the defender's remaining evasion, if any. Smaller weapon sizes usually have significantly higher tracking, with some exceptions.

Evasion is primarily based on hull type and is a defining feature of the Corvette, Destroyer, Transport and similar small ships. It can be increased by thrusters, by the combat computer for some hull sizes, and by Auxiliary modules like the Enigmatic Encoder and by having surplus power in the ship design. The evasion rate is capped at 90%, because of this, tracking higher than 90% has no benefit.

The formula to calculate the chance of a specific attack to hit the target is (remember that evasion is capped at 90 and accuracy is capped at 100):

$\text{actual chance to hit} = max(0, \text{accuracy} - max(0, \text{evasion} - \text{tracking})) +\text{chance to hit bonus}$

Generally, the goal is to pick a weapon that has just enough tracking to maintain the weapon's baseline accuracy, i.e. tracking equal to the enemy's evasion. Thrusters and Sensors mostly cancel each other out when on the same level, so without a serious tech disadvantage, the hull size and weapon sizes matter the most. Large weapons sport much higher damage than smaller weapons, allowing them to destroy their intended targets in just a few shots. However, since said large weapons also tend to have low tracking, ships with high evasion may become nigh-invulnerable to them as they can simply dodge the shots. Weapons with higher tracking, such as small weapons or missiles, are needed when engaging ships with high evasion, such as Corvettes. Conversely, small weapons have high tracking, ensuring that they are able to hit their target without missing much at all. However, they also have low damage and therefore struggle to deal with larger ships such like Cruisers and Battleships due to them having very high shield/armor/hull values, allowing them to absorb shots from small weapons without much difficulty. Large weapons with high damage are needed for dealing with ships that have such high durability.

Ship military power[]

Military power of a ship or a fleet is an estimate of its combined offensive and defensive capabilities. Armor and shields are weighted equally, while ship hull points get a 0.5 multiplier. Weapon damage per day and other properties of weapons, such as, shield and armor penetration, are factored in too. Ship evasion and speed are not part of this equation.

~~$\text{military power} \thicksim ( \text{effective health} \cdot \text{damage per day} )^{0.65}$~~

Force Disparity[]

Force Disparity is a combat bonus applied when a smaller force is engaged with a larger one (based on total combined fleet size) in battle and gives a bonus to the Fire Rate of all ships belonging to the smaller force. Force Disparity scales linearly with the fleet size difference, so, for example, a ship force that is engaging a hostile ship force 50% larger will have +50% fire rate, representing how the smaller force has an easier time maneuvering and targeting the larger enemy force. It caps at 100%, when fighting a fleet twice larger.

Force Disparity will never make a smaller force win unless it has a significant technological advantage. It will, however, ensure that all but the most overwhelming forces will take casualties and bear a cost for their victory.

Ship disengagement[]

Once a ship loses 50% of its Hull Points it will attempt to disengage. A ship that disengages will instantly leave the battle and rejoin the fleet at the end, until then appearing in the combat interface with a flag icon indicating that it has disengaged. If a fleet contains only disengaged ships it will make an emergency retreat.

Ships will never disengage if the owner uses the No Retreat War Doctrine policy. The presence of a black hole reduces disengage chance by half. Colossal ships cannot disengage.

The chance for a ship to disengage is the following: $\text{chance} = \frac{\text{damage}}{\text{hull}} \times 1.5 \times \text{ship multiplier} \times 1.25 \text {if within friendly borders}$

damage: Amount of damage the hit inflicted
hull: The ship's maximum hull points
ship multiplier: Ship type multiplier

Ship multiplier	Ship type
2	Science Ship
1.5	Destroyer, Cruiser, Transport Ship
1.25	Battleship, Titan
1	Corvette, Construction Ship
0.5	Colony Ship
0.2	Meteor Colony Ship

The chance for ships to disengage can also be affected by the following modifiers:

Source	Combat disengagement chance
Hit and Run War Doctrine policy	+33%
Trickster admiral trait	+25%
Erudite admiral trait	+10%
Energy minor deficit	−10%
Communications Jammer starbase building	−20%
Subspace Snare titan aura	−20%
Energy major deficit	−25%
Hell's Heart admiral trait	−33%
Unyielding admiral trait	−33%
Energy severe deficit	−50%
Energy catastrophic deficit	−75%
No Retreat War Doctrine policy	−100%

Initially each ship has only one chance to disengage. The chance is increased by 1 for any of the following:

Admiral level 5
Admiral level 10
Enigmatic Encoder ship component
Psi Jump Drive ship component

Emergency retreat[]

All ships of a fleet in combat have the opportunity to trigger an emergency retreat in the middle of a battle. This is a sudden escape using each individual ship's equipped FTL engine whether it is a Hyperdrive or Jump Drive that allows the fleet to escape destruction. The order is given by pressing the Retreat button in the combat sub-screen and the retreat can be triggered even from deep within the system. While on Evasive stance, a fleet will automatically retreat once the option is available. AI fleets in neutral or hostile territory will always retreat if half of the fleet is destroyed.

There are some tradeoffs, however:

The fleet will go "missing in action" upon a retreat for a number of months, depending on how far the ship was from its home starbase. As such it can be neither controlled nor attacked while moving back to its home starbase.
Ships require 30 days after entering combat before they can retreat.
The shock of the emergency retreat causes each ship to have a 25% chance to take up to 75% hull damage.
There is a 5% chance for each ship to be destroyed when retreating.

The chances to take damage can be reduced by Emergency FTL Damage Risk modifiers:

Source	Modifier
Hit and Run War Doctrine policy	−25%
Trickster admiral trait	−15%
Caravan Counter admiral trait	−10%

The 30 day charge time can be increased by Emergency FTL Jump Cooldown modifiers:

Source	Modifier
FTL Inhibitor starbase aura	+100%
Subspace Snare titan aura	+100%
Black hole	+50%
No Retreat War Doctrine policy	+50%

AI of fleets in space combat[]

Positioning[]

In combat each ships of a fleet will function independently. Ships have two modes of operation during combat: an attack-move-pattern and a passive-move-pattern, and they can switch between them due to conditions during the battle. For example, a ship with Swarm combat computer installed would

- pick a target

- turn on the passive-move-pattern and charge at the target until the distance to target is 10 (the so called formation distance),

- then, as formation distance is reached, the attack-move-pattern will turn on and the ship will start to orbit the target and attack it. This orbit radius is defined by the preferred attack range, and in this case it will be the minimal range or the smallest range among all weapons equipped.

In general the preferred attack range depends on the ship's installed combat computer and on the ranges of the weapons. The wording "medium range" for the Picket, Line, and Artillery combat computers should be interpreted as the mathematical median of all the weapons' ranges the ship has. As an example: if a ship has 5 weapons with max ranges: 30, 30, 30, 100, 150 - then the the ship medium range would be 30.

If the enemy ship moves closer than half of the ship's preferred attack range and the maintain distance combat behavior is active, then the ship will try to use a "back off" maneuver to return to its preferred attack range.

The condition for a ship to switch back from the attack-move-pattern to the passive-move-pattern is the following: a set return to formation distance is smaller than the distance from the ship to a chosen position in space, corresponding to the preferred attack range for target. In other words - the target it too far away.

This table gives a overview of all move patterns and distance rules used by each combat computer:


Combat computer program	Preferred attack range	attack-move-pattern	Formation distance	passive-move-pattern	Return to formation distance
Swarm	minimal range	Orbit	10	Charge	60
Picket	medium range	Stay at range	medium range	Orbit	maximal range
Line	medium range	Stay at range	medium range	Charge	maximal range
Artillery	maximal range	Maintain distance	medium range	Stay at range	maximal range
Carrier	maximal range	Maintain distance	maximal range	Stay at range	maximal range
Torpedo	10	Charge	10	Charge	maximal range
Platform	maximal range	Stationary	40	none	20

Targeting[]

Ship targeting is done in an automatic fashion using a system of weights and conditions during space combat. It is hidden from the player and can't be manipulated by the player. But it might still be helpful to know some of these mechanics used in the process. The exact mechanics is not fully known. However a bunch of values can be extracted from the Stellaris/common/defines/00_defines.txt file.

- There is a mechanic to target smaller or more fragile ships. The weight seems to be small.

- There is a mechanic for high-tracking ships to specifically target high-evasion ships.

- There is a mechanic for low-health ships (50% health threshold) to be priority targeted.

- There is a mechanic for closer ships to be targeted first.

- There is a mechanic to ignore and not target civilian and unarmed ships during space combat.

- There is a mechanic to for ships to be a bit less likely to target Starbases over military ships & defensive platforms.

- There is a mechanic for battleships, titans ( $\text{ship size} \geq 8$ ) to avoid firing on highly evasive targets (70% evasion threshold).

- There is a mechanic for missiles to re-target after they lose the initial target. First re-target success chance is 100%, second re-target attempt is 65%, third: 30%, fourth: 0%.

Name	Value	Description
COMBAT_BACK_OFF_RATE	0.50	When ships are attacking they will try to stay at max range and orbit their target. If the ship is closer than max range this value determines how fast it will "back off" in order to get to max range. 0.0 means that the ship will not back off and orbit with whatever radius it already has 1.0 means that the ship will prioritize orbit velocity the same as "back-off"-velocity. i.e a 45 degree angle
COMBAT_DAYS_BEFORE_TARGET_STICKYNESS	5	Combat must have gone on at least this many days before ships 'lock in' their target
COMBAT_TARGET_STICKYNESS_FACTOR	1.5	The higher this is, the less likely ships are to switch targets
RANDOM_TARGETING_WEIGHT	3.0	The higher this is, the more random ship targeting will be
COMBAT_SHIP_TARGETING_SIZE_MULT	0.03	The higher this weight is, the more likely smaller, more fragile ships are to be targeted first
COMBAT_SHIP_TARGETING_SIZE_MAX	10
COMBAT_SHIP_TARGETING_TRACKING_MULT	2.0	This weight is needed to ensure high-tracking ships target high-evasion ships
COMBAT_SHIP_EVASION_TARGETING_WEIGHT	2.0	The higher this is, the less likely ships are to target enemy ships with high chance to evade their shots
COMBAT_SHIP_LOW_HEALTH_THRESHOLD	0.5	The health threshold at which the low health targeting weight is applied
COMBAT_SHIP_LOW_HEALTH_TARGETING_WEIGHT	1.5
COMBAT_SHIP_DISTANCE_TARGETING_WEIGHT	0.002	The higher this is, the less likely ships will be to fire on distant targets
COMBAT_SHIP_DISTANCE_TARGETING_WEIGHT_MIN	0.10	Target weight can't be multiplied by less than this due to distance
COMBAT_SHIP_UNARMED_TARGETING_WEIGHT	0.005	The lower this is, the less likely ships are to target unarmed enemies over armed ones
COMBAT_SHIP_STARBASE_TARGETING_WEIGHT	0.75	The lower this is, the less likely ships are to target Starbases over military ships & defensive platforms
COMBAT_SHIP_EVASION_AVOID_MIN_SHIP_SIZE	8	Minimum size of ships that should try to avoid firing on highly evasive targets
COMBAT_SHIP_EVASION_AVOID_THRESHOLD	0.7	Above this level of evasion, try to find a less evasive target