Fallout 3

Story Related and Unmissable

After you've handed over the Tesla Coil to Tristan he will tell you to go to Adams Air Force Base, locate the Enclave's main base and destroy it. To get to the base you need to gain access to the Presidential Metro, the entrance to which can be reached by going down the Manhole guarded by a Brotherhood of Steel soldier outside the White House ruins.

Once inside find the door to the Metro and go through it. Inside there will be lots of Sentry Bots so make sure you've brought some Pulse Grenades/Mines. The Metro is littered with skeletons so take all the items lying next to them, one of which will be in a wrecked train and holding a Senator's Pass Card. You must take this as you may need it later.

Eventually you will enter a small room with a computer called M.A.R.Go.T, who will want to know who you are and what you're doing there. You can try persuading her you are friendly by:

1. Convincing her you're the President of the USA.
2. Using Science to give yourself maximum security clearance.
3. Using the Senator's ID Card.

After a long conversation she will tell you that the main fuse for the Adams Air Force Base train line has been forcibly removed but can't be replaced due to a security breach in the South East Tunnel.

This is where things get tricky as the "breach" has been caused by a load of Feral Ghouls so make sure your weapons and armour are in a good state of repair. When all those Ghouls are dead, move on to the Adams Air Force Base train line and kill all the Ghouls there. The Presidential Sentinel Unit will then replace the Fuse and the Emergency Lights will go Green so you will be able to take the train to the Air Force Base.

WARNING: Sometimes the Presidential Sentinel Unit will get stuck by the lockers in the narrow corridor. To unstick it just push it towards the Fuse Box.

On arriving at the Metro Station you will have to fight several Enclave soldiers and a Ceiling Turret (which can be hacked via a nearby terminal) before you can safely enter the base. After exiting the Station, head up the stairs and go left to see the Supply Crate which Tristan told you about earlier. Open it and take everything inside. One of the items is a Holodisk containing your orders so listen to them, then enter the little structure to your right and use the terminal to disable some of the nearby Turrets. There are several buildings in the area with Turrets on them so you will have to go the roof of each building to find the appropriate terminal in order to disable them.

WARNING: The area between the Hangers and the Air Traffic Control Tower suffers from major Frame-Rate and freezing problems so save, exit, reload the game and clear the cache on a frequent basis (see the Advice thread linked to in the Road Map for details).

You will find a switch on two of the rooftops, use them to trigger artillery bombardments on the respective areas to kill all the Enclave soldiers and save yourself some bother. Press the switches too often and they will break thus forcing you repair them before they can be used again.

On reaching the Air Traffic Control Tower, make your way inside and use the terminal up in the Tower itself to lower the Gang Way that's on the side of the Crawler. Before you enter the Crawler, go to the Storage building to the Northwest and clean it out but watch out for the Turret that’s inside above the staircase. After exiting the Storage Building, enter the Crawler and fight your way upstairs towards the Satellite Tower. There will be keys on the bodies of the Enclave Officers which allow access to the Mainframe, take them and make your way there. Use the terminals to unlock all the doors and disable all the Security measures.

Because the Level design of this section is so complicated, here's a video showing how to get from the Mainframe to the Uplink:

(Credit to Mahalo.com for the video. Although this is for the Xbox 360 version, the info is still valid).

At the Uplink terminal, you will have 5 options as to where to target the missiles:

1. The Citadel
2. Project Purity
3. Megaton
4. Rivet City Carrier
5. Adams AFB Platform

Option 5 is the one you want as nuking anywhere else will cause virtually everyone in the Capital Wasteland to hate you, which will make life harder in the long run. Exit the Crawler after deploying the missiles, watch all the cutscenes then you will be returned to the Citadel to be congratulated by Elder Lyons.

The trophy will pop after you have finished talking to Elder Lyons.

See here for a list of potential bugs and how to fix them: LINK (credit to the Fallout Wiki for the link).