To capture an enemy colony, send ships with troop capacity to their system and initiate a planetary invasion. You must first destroy all orbital defenses before troops can land. Raider-occupied planets can also be invaded directly once the garrison fleet is defeated or bypassed.
Troop Transports
Different transport types carry different numbers of troops. Military technology also increases the troop capacity of all transports.
- Troop Transport: 2 troops per ship. Unlocked by Combat Training. Cheap but fragile.
- Armored Transport: 3 troops per ship, with point defense. Unlocked by Composite Armor.
- Assault Transport: 5 troops per ship, with weapons and PD. Unlocked by Fortress Worlds.
Defenders: Militia & Garrison
A colony's defense force consists of militia (1 per 2 population, rounded up) plus garrison troops from military buildings. A planet with 8 population and a Barracks fields 4 militia + 2 garrison = 6 defenders.
- Barracks: +2 garrison, +15% ground defense, +3 system defense.
- Military Academy: +1 garrison, +15% empire invasion bonus, +10% defense.
- Command Bunker: +3 garrison, +25% ground defense, +5 system defense.
- Atmospheric Fighter Base: +1 garrison, +10% defense, +8 system defense, destroys 15% of attacking troops on landing.
- Defense Grid: +2 garrison, +50% shield defense, +30 system defense.
Combat Modifiers
Multiple factors multiply the strength of each side beyond raw troop count.
- Faction bonus: Some species are naturally stronger or weaker in ground combat.
- Technology: Military techs like Combat Training, Reinforced Armor, and Composite Armor boost ground combat and defense.
- Buildings: Defender buildings add percentage defense bonuses. Military Academies across your empire boost invasion strength.
- Orbital Bombardment tech reduces defender building bonuses before the assault.
- Atmospheric Fighter Bases destroy a percentage of invading troops before combat rounds begin.
Raider Invasions
Planets occupied by raiders can be invaded with troop transports just like enemy colonies. Raider planets have no orbital defenses once their garrison fleet is destroyed. Successfully capturing a raider planet reclaims it with 30% of its population as your colonists.
After Conquest
Captured colonies join your empire but suffer unrest equal to their population. Some native population survives. Fortify captured systems with Barracks and defense buildings to prevent counter-attacks.