One of the five admirals controlling one of the five Segmentae fleets.
A sector commander
Admirals local to Terra, often prospective sector admirals awaiting a sector to command. As such openings are rare it is far more common for solar admirals to be dispatched to war zones in command of a reinforcing fleet or kept busy on “special duties” with their own independent flotillas.
An admiral is allocated command of a portion of a sector’s fleet and responsibility for the security of a handful of star systems and vast tracts of wilderness space. It is rare for an admiral to amass his ships in one place, perhaps twice a century for major attacks or defense.
Commanders of the leading division of the fleet, typically commanding a light cruiser.
An honorific rank normally applied to captains in command of vessels on detached duty. A lord-captain can be considered a ruling lord in his own right, which can be an important destinction when dealing with arrogant planetary governors or petty administratum officials that may be inclined to dismiss the words of a “mere” Naval officer. For this reason many Rogue Traders have adopted the title of lord-captain.
While the Emperor may be the Master of Mankind, aboard a ship the Captain’s very word is His law. A Captains typically command the largest vessals that don’t require fleet support.