The first objective is actually killing those enemies at your base, but that's not necessary to do. Just destroying all the Weapon Caches is enough to complete the level. When there are 2 or more Weapon Caches next to each other, it's enough to destroy one of them since the explosion will automatically destroy the other ones next to it. I'm creating 10 Hoop Throwers to get a bit of extra XP, it's a Secondary Objective :) Not much else to explain about this level, pretty straightforward.