Combat and Invasions
Ship combat takes place when a fleet attempts to enter a tile occupied by a fleet owned by a hostile power.
At the start of combat, each ship will target an enemy ship of a type based on their role. If there are multiple enemy ships of the preferred type, the ship will choose one of them at random.
Interceptor, assault, and capital ships will begin moving forward on the battlefield towards their primary target. Support ships will not move unless all of the other types of combat ships in its fleet have been destroyed, at which point the support ships will also start moving towards their primary target. Escorts and guardians will not move unless the ship they are defending has started moving forward as well.
A ship will only stop advancing once it is even with the target ship, and will move further only if the target ship moves out of range.
Whenever a weapon is ready, the ship will fire on its primary target. If its chosen target is out of range, it will attack another nearby ship. All weapons of similar type on the attacking ship will fire as one single attack. Hits on a target that has a correlating defense (point defense for missiles, shields for beams, or armor for mass drivers) will do damage to the defense itself. Damage done to a ship’s defense is displayed in orange on the battle log.
Hits on a target with no remaining defense of the appropriate type will instead do full attack damage to the ship’s hit points. Spacecraft (ships, starbases, and shipyards) that are reduced to zero hit points are permanently destroyed.
Combat continues until all of the ships from one side are destroyed. Retreating once a combat has been initiated is not an option.
There is no retreating from combat for either the attacker or defender. Combat proceeds until one side or the other is annihilated.
The Combat Viewer shows your ships fighting against your enemy. Combat in the game is automated, so once you’ve chosen to engage you can either “auto resolve” the combat or watch it play out. Whichever you choose, it has no effect on the outcome of battle.
Certain military starbases modules give powerful fleet-wide bonuses to any combat that takes place within their area of influence. It may be helpful to try and lure enemy fleets into the range of the Starbase before engaging in combat.
Damaged starships repair at a base rate of 1 hit point per turn, whether they move during the turn or not. Starships that end their turn in orbit around a planet repair at a base rate of 5 hit points per turn. Starships that end their turn in a shipyard repair at a base rate of 4 hit points per turn. Starships that end their turn in a starbase repair at a base rate of 6 hit points per turn.
Certain technologies (for example Healing Hulls and Living Ships) and ship components (like Structural Enhancement Field or Repair Drones) enable tactical repair, which allows a ship to repair itself during battles. This can be quite valuable, as a fleet can take damage during a battle yet emerge from it at full health.
The mix of ships in your fleet is incredibly important to its success in battle. Equipping support ships with appropriate modules, ensuring ship roles are handled well so you don't have vulnerable carriers engaging point-blank with enemy destroyers, and other similar tactics can multiply any force's capabilities.
One strategy that seems to work well is a mix of escorts and capital ships. Design your own ships (and don't forget to manually assign the role if the game defaults to another) such that your escorts have high defenses and low attack, and your capitals have high attack and no defenses. All enemy ships will attack your escorts first, wasting their firepower on their defenses, while your capitals are free to fire at the enemy.
Ground invasions are the usual method of conquering enemy planets. Transport ships equip people from a friendly colony with appropriate gear and carry them across the void to an enemy world that has been cleared of space-based defenses.
How to Invade (pre Crusade expansion)
Invading: Transports bring “Soldiers” to a target planet. “Soldiering” modifies the amount of people you bring. So, a transport with 4 people with a 50% soldiering bonus is the equivalent of 6 Soldiers.
Defending: A planet's defense is determined by 3 things:
Any invading troops that made it through the Planetary defense system land and take out one tile at a time. The casualty rate for both sides is dependent on what invasion methods and tactics are used. For this example, we will say the invader has a casualty rate of 50%, which is pretty high.
Tile 1, 3 Invaders > 1 Defender, Invader wins, but loses 1 soldier Tile 2, 2 Invaders > 1 Defender, Invader wins, but loses 1 soldier Tile 3, 1 Invaders <= 1 Defender, Invader loses, invasion repulsed.
This is a really simple example, but is more or less how it works. The strategy comes in with the invasion types, since these can modify Soldiering, Resistance, and Planetary Defense.
Unlike in GC2, invasions do not kill everyone on a planet. Depending on the invasion type, the casualties can vary from light to genocidal. As each tile falls, a certain amount of defenders will survive. If the invader wins, they will become part of the planet's population after the invasion is over.
Some invasion types are so horrific that they will do damage to the planet or destroy improvements. Sometimes, there are additional long term effects, often leaving the invaded planet with durational modifiers, like low approval for X number of turns.
If you've researched appropriate technology such as Biological Warfare, you can pay credits to enable special tactics during an invasion. Biological Warfare, for example, reduces the enemy's ability to resist your assault while simultaneously reducing the chance for existing improvements to be damaged during the invasion.
The ability to resist a ground invasion depends on planetary defenses, resistance, and soldiering ability.
Resistance determines the percentage of the planet's population that will try to defend the planet from an invasion. The rest of the population will suffer losses from the invading force, but they do not assist in repelling the invaders.
Legions and General Citizens
When you create a general citizen they add five legions to your global pool. These legions can be loaded onto a transport or stationed on individual planets for defense. Once you do this they can't be put back into the global pool.
When you assign a general to a colony they will bring with them 5 defending legions, however these legions are NOT subtracted from the global pool. They will defend the planet the same as if you stationed them as a garrison but are not permanently assigned to that colony. If some die during a failed invasion those will be subtracted from the global pool. If you still have legions remaining then they will be able to defend the colony again without having to use the station garrison project to reinforce the colony. If you place generals on more than one planet, then each planet will get 5 defenders from the global pool, however since it isn't removing any legions from the global pool (unless they are killed), you can have the same 5 legions (or as many as you have if you have less than 5 in the pool) guard more than one planet. General citizens grant you free legions while also letting you defend more planets with fewer legions, allowing you to either have a large reserve for defense, or a bigger supply for invasions.