Deus Ex/Area 51

Ground Zero
The missile strike damaged the area outside, but there are a few soldiers in hiding.

The immediate threat is the sniper in the tower directly ahead. Hug the wall around the helipad, or take out the sniper from your current position. You will need to enter the tower to open the blast doors leading to Area 51, however, there are live LAMs at the first ladder from ground level.

When you approach the blast doors, Walton Simmons will approach from the Comm Building (if you haven't defeated him already). As with the last encounter, he will use a plasma rifle.

The hangar contains a few MJ12 troops, and an alternate route into the base though the vent.

If you enter by the front door, the camera in front will first try to trigger the alarm. There will also be two medium security robots on patrol. You would first need to activate power to the elevator past the right passage, then turning on the generator. The elevator can then be used to reach the inner facility.

If you want to enter by the vent, the cheapest way is to jump on top, and destroy the fan. When you jump down, you should land in water. If desired, you can swim deeper to reach a laser mod. Head down the side corridor to reach the elevator area, and the entrance to Area 51.

Entrance
The first room has a camera-triggered turret, and a blue laser grid. Jump over or disrupt the grid to avoid releasing mini-spider bots. However, the first generator will begin to signal an alarm as you approach - it will explode after a few seconds.

Morgan Everett will try to speak with you through the comm station. He will relay the code for the local crew area, 8946, and warn you about Tracer Tong. This code allows you to reach the barracks, and recreation. You can find a code here, 0169, that opens one of the beds in the barracks, where you can retrieve the Sector 3 key.

Proceeding further south leads to a group of soldiers, including a sniper. It also is the entrance to Sector 3. Use either the key, or use enough picks to clear the 90% door strength.

The first room in Sector 3 is an elevator leading down. However, an MJ12 soldiers and a MIB will come out of the elevator and prevent you from passing. Page will comment on your performance, based on how much damage you receive.