AI War:Ion Cannons
What Do I Do About Ion Cannons?
A: To destroy an ion cannon, you'll need to have ships equal to or greater than the level of the ion cannon, or you'll need to have a LOT of lower-level ships. Ion cannons insta-kill any ships with a equal to or lower level than themselves, but they can only one-shot about one ship per 1 to 4 seconds (depending on ship cap level). So if you bring a few hundred ships, this gives you time to work (but it will be killing your higher mark ships first). You can use this tactic to get yourself closer to the ion cannon and destroy it, or you can use it to slip scouts or other ships past the planet, avoiding it.
Do note that it isn't always a given that you want to destroy ion cannons. If you can capture the planet without destroying them, the ion cannons will become yours, helping you to defend that planet against future enemy waves. You might take more losses in the short term, but the longer-term payoff is sometimes worth it. Do note that Mark III and higher Ion Cannons have an AI Wave Multiplier that can be quite nasty. These structures in particularly are viewed by many players as high value scrap (even 10% of 5,400,000 resources will nearly cap you out).
Ships That Are "Immune To Being Insta-Killed"
Ships that have the ability "Immune To Being Insta-Killed" cannot be hit by ion cannons at all. This includes golems, starships, bulletproof fighters, armored warheads, and various other specialized ships.