Joining this well-armed (and some might say zealous) faction begins whenever you wish, after you (optionally) listen to Military Frequency AF95 and visit Cambridge Police Station, or you observe a giant airship flying overhead and mooring at Boston Airport. You can continue Brotherhood of Steel operations for as long as you wish. However, be aware that your relationships with the other main factions—the Institute, the Railroad, and the Minutemen—may be impacted negatively the more you pursue your career as a Brotherhood soldier. Be warned—you may need to learn some Latin.