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While the Mid-western Brotherhood defends you but wants something in exchange (new bodies, ability to trade, etc) the Fallout 3's Brotherhood just defends you. Although it is done rather stupidly take for example how the two defend the locals. However if all cards aren't collected, access may be denied. Fallout 3's Brotherhood is a direct copy of this. If Cassidy is your follower then she will talk to the girl in the room, when she is distracted you can swipe his card. For Taggart, you may need a Stealth Boy as the only time you can steal his card is when the girls view is blocked by the tower in the middle of the room. At the end is the self destruction room, where you will also find Taggart. Go back towards the door to L1 and go all the way up the left hallway this time.
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Crouch, wait until you are hidden and then steal his key card. He will be in the room sleeping, standing, or on his computer. Hardin can be found to the left of this room in one of the three bedrooms. Head right, where you can find McNamara, who is the easiest to steal from and can be stolen as he is sitting in his chair. You need to go level L2 of the bunker, where you can find Elder McNamara, Head Paladin Hardin (Or Head Paladin Ramos based on your choices) and Head Scribe Taggart.
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It is suggested that you save before stealing from each character in order to avoid killing for the keycard if they catch you stealing. Once you have access to the bunker, you need to steal 3 keycards from 3 main personnel in order to get the password for the self-destruct sequence or have a Science skill of 100, at the same time you can look for a bunker key for your escape later on. After you have gained the Brotherhood's trust, you can enter their bunker.
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