- 1). Play through the game normally until the final assault on the Jefferson Memorial. You will have Liberty Prime --- a giant robot with a death ray --- and a troop of Brotherhood of Steel Paladins on your side.
- 2). Follow Prime and the Paladins to the Jefferson Memorial, then enter the Memorial once you reach the entrance.
- 3). Kill the Enclave soldiers --- by this point you should be nigh unbeatable, especially with the Brotherhood backing you up --- then continue straight through the Memorial into the Rotunda area. You will find Colonel Autumn in here waiting for you.
- 4). Kill Colonel Autumn. He will go down easily, especially since you have Sentinel Lyons keeping him busy as well. Use stim packs if needed and just keep hammering on Autumn with your strongest weapons until he bites the dust. Speak to Sentinel Lyons after Autumn dies --- he will be nearby after the fight --- then ascend the stairs in the center of the room and go into the Project Purity control room.
- 5). Enter the code "216" using the control panel, then sit back and watch the ending cinematic roll.
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