Admirals don't command starships. They command captains to take them where they need to go.
Any rank above Lt Cmdr. First Officer ranks don't matter that much, as long as they have seniority over the rest of the crew.
An admiral in command of a starship would most likely be an exceptional, temporary situation. In that case, it's likely that the ship's appointed captain--regardless of his or her rank--would serve as executive officer for the duration ProfessorTrek 01:06, August 8, 2011 (UTC)