In the quest Where you get the remenants power armor and the gannon family tesla armor (power armor) which are the best armor types in the game. the enclave remnants, in the remnants bunker (near jacobstown) Can offer you power armor training.
have arcade gannons tally system positive (visit silver rush, crashed vertibird etc.)
follow either yesman, mr house or ncr. leigon are excludedfrom this oppotunity.
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This is the quest to get this. it can be easily and permenantly blocked through wrong actions in the game, so make constant saves.