Stop the Enclave

Stop the Enclave is an unmarked quest in Fallout 2. To complete it, you must overload the reactor of the Oil Rig, and then kill the final boss.

Quick walkthrough
Reach the Oil Rig, force Tom Murray to blow up, defeat Frank Horrigan and get out alive.

Detailed walkthrough
When you reach the oil rig through the PMV Valdez tanker, you will have to infiltrate the Enclave base.

Into the Oil rig
After entering the oil rig, you must first walk through the southern part to the stairs. You must have advanced power armor, or else the Enclave soldiers will attack you on sight. Even with advanced power armor the presence of any companions will cause the soldiers to attack you. You may simply let them wait at another location to avoid alerting the guards. After walking around the stairs, you will see people in cells. Talk to them, and you will find there are people from your tribe, and people from Vault 13. Speak with your Village Elder, you will learn you must melt down the facilities reactor.

Dick Richardson
Now you must go down the nearby stairs, and have to solve the electric floor puzzle. Soon after passing the puzzle, you will come face to face with Dick Richardson. Who will offer amazing amounts of historical and important information to you, mostly as a stalling tactic. You are allowed to kill him, and this is the only way to obtain the Presidential Keycard.

The following options are available:
 * Use many super stimpaks on him, and then use the Pipboy's wait function for the after effects to kill him (Enclave not alerted).
 * By reverse pickpocketing him with an active explosive and leave to another section, he will either die or be weakened (Enclave not alerted).
 * Just kill him (Enclave alerted).
 * Sneak and shoot him, if he receives a critical hit, he will die (Enclave sometimes alerted, sometimes not).

Blowing the reactors
When you are done, you can go behind his office, and find stairs in the back. Walk down, and keep walking, until you find a reactor. It is recommended to have a plastic explosive. If you have one, you can place it near the reactor. If you do not have one, you may have to overload the reactor manually. There is an alternate process through Speech/Charisma. Though you can perform the process above, if you have a high enough Charisma, and possibly Strength, you can speak directly to Tom Murray (the head of the Atomic Energy Commission of the Enclave) to overload the reactor by taking the stairs down the corridor to the left of Dick Richardson's room.

Tom Murray is wearing a lab coat, and can be found in the only room with red carpet on that level. Tell him that you need to shut down the atomic reactor, and if he doesn't tell you how to do so, you are going to shut him down permanently. At this he will tell you that shutting the atomic reactor down too fast will cause a meltdown. Tell him that if he doesn't do it, you're going to "gut him like a fish". At this, Tom will agree to do it out of fear for his life, next responded with you do not care, and to do it anyway.

Facing the impossible
After you've said this, tell him he did the right thing, and that he better stay in his room and keep quiet. When you are done, retrace your steps to the main entrance. Here, you will face Frank Horrigan.

With a decent speech skill, you can convince the Enclave team in the room next to Horrigan to fight in your corner, proceed through the obvious speech phrases and the one you are looking for is the phrase that ends with you saying 'unless...', this is where the speech check is won or lost, if he laughs it off, try again, if he sounds concerned you're on the right path. If you fail, you can easily re-try through the exact same dialog. These teamed with the presidential keycard will ensure a speedy success.

Using the keycard
The fight is extremly difficult unless you have the Presidential keycard, which allows you to use the turrets to attack Horrigan (they will deal 15-40 damage). If you have the keycard, use the terminal in the SW corner of the boss room and follow these phrases: ,'Help', 'Yes', 'Back to log on', then it is the top phrase about counter insurgency. This will ensure that the turrets are on your side, and with the Enclave troops as well, Horrigan stands very little chance. When he falls, you can talk to him or kill him yourself (after talking to him he dies). Then, escape from the Oil Rig.

Oil rig nuked
After Chosen One escapes, there is a scene where the Oil rig and its inhabitants got destroyed in a big explosion. After this, depending on Chosen One's actions, diffirent endings appear.