The Imperial Assault ability is currently only available on the Super Star Destroyer (Evil Empire). To perform this attack, an undamaged Super Star Destroyer needs to drop at least ten clans on an enemy planet in a single turn. Once this is performed, the planet will be captured. This will work against all planets and there is no effective defense once the Super Star Destroyer is in orbit. The assault will immediately destroy all defense posts and enemy clans.
An Imperial Assault will only take place if the Super Star Destroyer is undamaged at the moment of planetary assault. If the vessel is damaged at that time, the troops will still drop, but it will be as a standard Ground Attack. (For timing purposes, Imperial Assaults take place during the normal sequence in the Ground Attack phase.)
This mission is automatically activated when the Super Star Destroyer transfers ten or more clans to a planet not controlled by the owner of the ship. In order for this mission to function properly, all the requirements of a Foreign Cargo Transfer must be met.
The Super Star Destroyer also has the Planet Immunity ability.