Here are some basic rules concerning who will fight. More details are below in the phase descriptions:

  1. Units must be at the very same position (same X,Y) on the map to be able to fight.
  2. Fuel-less ships cannot attack.
  3. Fuel-less ships cannot be attacked (except by planets with friendly code NUK).
  4. You will attack all enemy ships when you have mission Kill. You can choose to attack only one race by selecting them as Primary Enemy (and not using the kill mission); recent PHosts allow you to combine that with a permanent global enemy setting. If you have neither the Kill mission, nor a Primary enemy, you will not attack anyone. You'll still defend yourself when attacked. You cannot attack players whom you have offered a combat level alliance.
  5. Cloaked ships cannot be attacked.
  6. Cloaked ships can attack other ships if so configured (AllowCloakedShipsAttack), but cloaked ships cannot attack planets.
  7. Objects with matching friendly codes do not attack. Remember that special friendly codes never match.
  8. (4.0k) Units will not attack each other if they have no offensive potential against their opponent.

    This rule applies in two cases: (a) Two freighters will never attack each other, nor will ships without ammunition and beams. (b) A ship will not attack an unarmed planet if it has only death rays. Death rays are ineffective against planets.
  9. If a planet takes part in combat, and that planet has a starbase, those will combine their power and fight as one unit. It is not possible to attack (or defend with) just the planet or just the starbase.