Ground armies are used only for defense during an invasion or when you want to conquer an enemy system. You don't have to train them separately like ships. Ground armies are based on the amount of fleet crews and defense forces in systems. The second value can be increased by building certain military structures or by assigning a hero that can increase it. When it comes to ships it all depends on the size and number of special support modules that increase the amount of people in a given ship. Bigger ships have more bonuses for those modules so you can think about making a specific type of a ship with a lot of support modules and with a small amount of weapons. This "invasion" ship will only be used for assaults and conquering planets.
A ground battle happens when a fleet is orbiting a system in which there are no enemy fleets that can interrupt an invasion. First, if you want to initiate a ground attack you must start with a system blockade. If forces on a planet are stronger than yours you can wait with an attack. Because of a siege, a defender's garrison gets smaller with each turn. Some modules can speed up this process. However, it is usually better to start a ground battle because you can avoid a counterattack by enemy's fleet or a situation in which you were close to take over a planet but you were forced to sign a peace treaty.
A ground battle is similar to those that take place in space. After selecting a tactical plan you can see how your forces are doing on a planet. Before that you can add heavy equipment or upgrade your units in Military screen. Some race bonuses can help only when you are attacking or defending a system. Usually, it is an additional attack before a main battle or an increased number of soldiers in a system. As you can see your options, when it comes to helping and supporting your army, are very limited.
When you are attacking you can select one of the three following tactics:
- Preemptive Bombing. You damage enemy's army before an attack but you increase your chances in damaging improvements and/or killing population.
- Infiltration. A round is longer but the attacker has bonuses to resistance at the expense of attack power.
- Blitz. A quick attack that deals a lot of damage but is also deadly for the attacker.
If you are defending you have similar choices:
- Local Resistance. You receive additional units but you must spend one representative of a race. A useful option if you don't have a lot of units in garrison or your reinforcements will take some time to arrive in your system.
- Protect System. A head-on battle. Defender's army has more health points but the loses in civilians and buildings are smaller.
- Surrender. You give up a system without a fight. This option is useful if you want to avoid destruction in a system and you have already sent a fleet to help the defenders.
Your choice of ground army is unlocked with your technology progress which allows you to change your units. You don't have to train or buy new units. You just have to enter the Troop Management menu. Here, you can increase the usefulness of various types of units by paying a certain amount of money. An upgrade is immediate. You can also increase the number of a given type of unit in your army. The army created in this screen will appear in every ground battle, invasion or defense.
- Infantry is the basic type of units, you can enhance them by using better anti-aircraft attacks.
- Armour focuses on receiving damage and crushing infantry but it has problems with fighting aircrafts.
- Air is the best and the most expensive, when it comes to upgrades, type of units that you can have. Deals a lot of damage and has a decent amount of health points. Its goal is to destroy Armour units.
If you plan on having many ground battles you should remember to have a suitable amount of crew in your fleets so your ground armies will have more units. You can build a few ships that have support modules that increases the number of crew. If your enemy uses only Infantry then you must develop Armour units as quickly as possible. If they also use these units then get Air units and upgrade your Infantry. But remember that in this game wars are won not on planets' surfaces, but in space.