This quest becomes available immediately after completing the Brotherhood of Steel Quest: Call to Arms. Continue through this brief mission to officially become a member of the Brotherhood of Steel.
Return to Cambridge Police Station
At the end of the Brotherhood of Steel Quest: Call to Arms, Paladin Danse will reward your efforts with his Righteous Authority laser rifle, and an invitation to join the ranks of the Brotherhood of Steel. Accept his offer to join the faction, and then head back to Cambridge Police Station.
Speak with Paladin Danse
When you return to the Cambridge Police Station, Paladin Danse is having a chat with Scribe Haylen and Knight Rhys regarding your membership status. Much to their chagrin, Danse feels you have the potential to aid the Brotherhood with their cause, so he decides to officially induct you into the Brotherhood of Steel. Congratulations!
If at this point you have not yet reached Main Quest: Act II, you will be given the rank Initiate. But, if you’ve already completed the Reunions main quest and have started Act II, you will be inducted with the rank of Knight instead, activating the Brotherhood of Steel Quest: Shadow of Steel.
Support the Brotherhood Recon Team
After speaking with Paladin Danse and his crew, the quest concludes. This also unlocks the Semper Invicta achievement for joining the Brotherhood of Steel faction. Now that you’re an Initiate, it’s time to put in some work for the faction to show your support.
Scribe Haylen and Knight Rhys will now have assignments available for you. Speak with each of them to obtain the Quartermastery and Cleansing the Commonwealth Radiant Quests. These quests can be done repeatedly to earn additional XP. Completing either of these Radiant Quests will also grant access to the Brotherhood of Steel Miscellaneous Quest: The Lost Patrol, which is assigned by Paladin Danse.
Although Radiant Quests are repeatable, keep in mind that completing quests for the Brotherhood of Steel will cause you to lose favor with other factions. In order to proceed with the next quest for this faction, you need to first complete the Main Quest: Reunions. The Brotherhood of Steel Quest: Shadow of Steel will become available at the conclusion of Act I.