A battle occurs when an attacking fleet reaches a defending planet.
A battle consists of 1 to 6 rounds in which both sides perform attacks. The battle ends once at least one side has lost all their ships and defenses or at the end of the 6th round, in which case the battle is declared a draw.
The attacking fleet will only be able to plunder resources if they win (by destroying all opposing ships and defenses). Information on a planet's technology, defences and resources can be obtained before battle through espionage.
While the precise method of calculating each round is not completely known it is currently suspected that it is close to the following (from another game with similar combat mechanics):
"In the beginning of each round, every unit starts with its Weaponry (with value W) and Shielding (with value S) at its initial value (specific of each ship plus technology upgrades). The Hull Plating (with value H) has the value of previous round (initial value of the ship if it is the first round).
In each round, all participating units(defenses+ships) randomly choose a target enemy unit.
For each shooting unit:
For every unit that ends the fight with H <= 0, it is destroyed and thus does not appear in the next round. If every unit of a side (attacker or defender) is destroyed at the end of the round, the battle ends with the opposite side winning.
After the combat, each defensive structure of the defender has a 70% chance of being immediately rebuilt without additional costs."
It seems likely that the 70% value for rebuilt defenses is currently closer to 30%. Also, a March 2014 update to the battle mechanics (an optimization to decrease server load) might mean that the bracketed comments of point 4 are no longer true.  After battle all destroyed ships will contribute to debris floating around the planet.
If an attacking player destroys all defensive ships and structures by the end of the 6th round, they will have won and will be able to plunder (steal) resources from the planet they attacked.
The number of resources they plunder will be some percentage of the total resources held by the planet (determined by the level of the planet's underground bunker, as well as the glory score of the player whose planet it is), but they cannot take more than the total capacity of all the cargo ships that remain in their fleet.
Also known as Calculators.
Simulators are tools that estimate the result of a battle. One such simulator designed for Galaxy at War Online can be found here. This simulator might provide insight into combat mechanics.
Simulators for another game with similar combat mechanics and ship types. One example can be found here, note the following:
- Recycler = Recovery Vessel
- Espionage Probe = Spy Probe
- Solar Satellite doesn't exist in GaW Online.
- Battlecruiser = Dreadnought
- Blueprint Ships don't exist and can not be calculated yet.
- Deuterium = Gas
Since this is for a different game and GAW game mechanics aren't currently fully understood, one should be careful in putting too much trust into the results of current simulators. Also remember that there is a random element to battles (the targets chosen and hull explosions) which could affect results.
The first simulator designed for Galaxy at War Online is now available at . This simulator is free, and might provide more insight into battles than alternative simulators made for other games.