Walkthrough: This is a very short mission during which you won't encounter any hostile units. You should end up inside the Sparta base after watching several cut-scenes. Make a few steps forward and talk to a merchant #1. Notice that you'll be allowed to take whatever you need FOR FREE, including better guns. Make sure to take a look in the ammo case #2, collecting dynamite sticks, standard ammunition and 30 rounds of gold ammunition. Finish off by checking the area to your right - you can pick up a gas mask, filters and nightvision goggles.
You may now proceed to your left, choosing a narrow passageway located near a parked vehicle #1. Get to the upper level where you'll have to talk to the commanding officer #2. This mission will end after a short debriefing (and after you've pressed the left mouse button).