Shadow of Steel Main Story, Brotherhood of Steel Quest
This quest will be triggered or can be aquired when you complete Semper Invicta quest.
Related points of interest
Stages of "Shadow of Steel" quest
2. Board the Vertibird
Now that the Brotherhood of Steel's reinforcements have arrived, Paladin Danse has ordered me to accompany him up to their flagship, the "Prydwen."
It's on the roof.
5. Attend Elder Maxson's Address
The Prydwen's captain, Lancer-Captain Kells, has ordered me to attend an address being given by Elder Maxson, the supreme commander of the Brotherhood of Steel.
7. Report to Paladin Danse
Elder Maxson has promoted to the rank of Knight and awarded a full suit of Power Armor which I can find on the Prydwen's Main Deck.
8. Quest completed
Paladin Danse has become my sponsor and offered to accompany me as a guide as I travel around the Commonwealth.
From now, Paladin Danse can be your companion.
Next / new quest is Tour of Duty (Main Story, Brotherhood of Steel).