From your vantage point, observe the base. You'll see several Omega Force soldiers patrolling. Your primary goal is to disable the alarm system, usually located in a central building or tower, to prevent reinforcements from being called. Use your binoculars (hold Z) to tag enemies, making them visible on your mini-map and through walls. This is crucial for planning your approach.
There are multiple ways to infiltrate. A stealthy approach is often recommended to conserve health and ammo. Look for unguarded entrances, vents, or climbable structures. Prioritize taking out snipers or heavy gunners first if they have a clear line of sight. Once inside the base, locate the alarm panel. It will be marked on your HUD. Interact with it (E) to disable it. Be wary of patrolling guards inside the buildings. After disabling the alarm, prepare for a brief encounter as you make your way out or to the next objective.