Rank
Ranks are unlocked while progressing through the game (?). Appointing a companion to a specific rank provides some benefits, but costs [Influence] and increases their [Wages]. Each troop can have one Captain and multiple Lieutenants.
Captain
Promoting a companion to Captain automatically teaches them the skill [Galvanize] and allows them to be assigned to the [Strategy Table].
Lieutenant
Promoting a companion to Lieutenant automatically teaches them the skill [Galvanize].