oh wait are you talking about the bases at the end of the level??? or like what looks like a base during the level where there is a few things moving back and forth amd flashing that you get 1000 points each for killing them?

the latter, the places with all the moving things. You destroy all the moving things or flashy red parts and the hatch to free the dudes. I should have been more specific and said The bases with dudes in them. Usually 2-3 per level before the end base.

ahh yes, i think you are right about this. yeah that is what i did to get the screen to change. this really is a cool game!!!