Small addition to good Apocalypse strategy. Place Ion Cannons and Bunkers on the first row: IBIBIBIBI. It will save 50B cash, give double population protection to 3 middle Ion Cannons which should be upgraded first. When you have enough cash build Bunkers in the second row behind Ion Cannons, and sell the ones in the first row. Replace them with defences.
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 "PlanetDefender"){kind=icon}