Most of the warfare in Stellaris is settled through space combat. Though occupying planets is necessary to achieve ultimate victory, landing armies is safer once the fleet has eliminated the threat of enemy vessels intercepting and destroying vulnerable transports. Winning battles in the stars is about bringing enough weapons and power to the battle, yes, but also about having the right loadout to defeat the enemy.
There are three basic weapon types in Stellaris. Choosing a primary weapon type is part of species creation. Pre-made species have their primary weapon already selected. Primary weapon choice only affects which weapons are researched at the start and which weapon you can put onto spaceports at start - all weapon types can be researched, but the basic technology has to be researched first. Each weapon has a counter-measure to it, meaning that the empires weapon choices are likely to evolve as it encounters advanced empires that build ships that thwart the primary weapon type.
For a detailed overview of performance of each Weapon Type and counters, see Ship designer.
Combat in Stellaris takes place in real time, mostly out of the player's control. 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 creatures 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 the results 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 results 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.
Damage of space combat is distributed onto three components of ship: hull, armor and shield.
- Hull is most important attribute for any ship. When hull reaches 0, ship will be destroyed and removed from battle regardless of any other attributes. When the hull is damaged, the most common way to repair it is sending the fleet back to a spaceport. It is possible to repair hull other than docking, like the component regenerative hull tissue, admiral trait engineer and space station aura nanobot cloud. However, self repairing is much slower than in-dock repairing (1% per day or 30% per month). Military stations have a base self-repairing rate of 1% per day. It take 30 days before a ship can be repaired after damages and 10 days for station to repair itself after combat.
- Armor isn't guaranteed to absorb a fixed value of damage like hull or shield do. Instead, the ratio of damage on the hull to damage on armor is given by damage reduction. Every ship has a base armor, and it can be improved by installing additional armor modules at higher cost of . Damage reduction cannot exceed 90%. In that case, the damage to the hull is 1/10 of the damage displayed in ship-design menu if the weapon has no effect on armor.
- Shields provides additional protection for ship. It is created by shield modules on board, and has a much faster regeneration rate than the hull. Installing a shield module requires and . Since most systems on board require to work, it is necessary to balance power, shield and other components when designing a ship. The shield is the outermost cover of a ship. Before running out, the damage of a weapon is 100% absorbed by the shield if the weapon has no special effect on the shield, while the hull and armor receive no damage at all. Shields are crucial for continuous battles, since it can be quickly charged between small gaps of combat while the hull cannot.
When being attacked, the shield will absorb damage first. After the shield is breached, the further damage will be distributed between the hull and armor according to the damage reduction. However, some weapons have effects that can deal damage directly onto the hull:
- Armor penetration: This allows the weapon to ignore certain percentage of Damage Reduction (not always proportional to Armor Value). It doesn't work if the target ship has remaining shield.
- Shield penetration: This allows the weapon to ignore a certain percentage of shield, dealing the remaining damage directly on the hull and armor.
- Shield damage: This is the ratio between bonus damage to the shield and damage delivered by the weapon. Most weapons have this value at 0%, meaning that the damage to the shield is the same as the original damage value of the weapon. Shield damage at +100% means twice as many damage is caused by the weapon, while -100% means the weapon will never have any effect on the shield. The damage doesn't matter to the hull and armor.
For example, Arc Emitter and Focused Arc Emitter have 100% armor penetration and 100% shield penetration. During combat, the damage they deliver is exactly the value of enemy hull damage received, regardless of enemy shield and armor.
Damages to three parts can be calculated by certain formulas.
- Damage to the shield is simply weapon damage multiplied by (100% + shield damage bonus).
- Direct damage occurs when the shield runs out or a weapon has shield penetration effects. To calculate damage, the damage reduction percentage (DR%) is needed first. Relation between DR% and armor can be found in Armor. Damage to armor is give by
while the rest of the damage goes to the hull.
Accuracy, Tracking, Evasion
Three parameters determine the chance of a weapon to hit its target: accuracy (or chance to hit), tracking (ability to counter evasion) and evasion (or chance to avoid) of enemy. The first two come from the weapon itself and accessories (combat computers, sensor and auxiliary utilities) on board.
Accuracy comes primarily from the Weapon. High accuracy weapons are usually countered by evasion, if tracking is lacking. In turn low accuracy weapons will not suffer additionally against decent amounts of remaining evasion. Generally weapons with low range or rate of fire have very high accuracy to ofset the few shoots they can fire.
Tracking comes primarily from the Weapon as well. Tracking will cancel out enemy evasion, and the real chance to hit is determined by weapon accuracy and remaining evasion. Smaler weaponsizes usually have significantly higher tracking, but in particular missiles and the Destroyer have noticeably high tracking.
The evasion is primarily based on the hull type and is a defining feature of the Corvette, Destroyer, Transports and similar smaler ship sizes. However it can be increased by having surplus power in the ship design, having the best available thrusters, the combat computer for some hullsizes and adding Auxiliary modules like the Enigmatic Encoder. The evasion rate is capped at 90%.
Remaining evasion (Evasion minus tracking) effectively acts as a cap on accuracy and a weapon incapable of countering Evasion will miss as if it had a much lower accuracy. The chance to hit is 100%-Remaining Evasion or the Accuracy of the weapon, wichever is worse for the attacker. The game considers remaining evasion and accuracy for target selection of ships and every specific weapon.
The formula to calculate the chance of a specific attack to hit the target is:
Generally the goal is to pick a weapon that has just enough tracking to at least maintain the weapon baseline accuracy. Thrusters and Sensor mostly cancel each other out when on the same level, so without a serious tech disadvantage the hullsize and weapon sizes matter the most.
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 jump to light speed 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.
There are some tradeoffs, however:
- Warships require 30 days before they can retreat. Civilian ships require only 7.5 days.
- The shock of the emergency retreat will cause damage 20% hull damage. Ships with less than 20% HP have a 50% chance of being destroyed, otherwise will arrive in friendly space with 1 HP.
- The fleet will go "missing in action" upon a retreat for a number of months, depending on how far the ship was from friendly space. As such it can be neither controlled nor attacked while moving back to friendly space.
- There is a 1% chance for each ship to be forever lost when retreating.