High Admiral was the title born by the commander of Navy forces within an Imperial Sector Group. Along with the Army title of Surface Marshal, this title was typically borne by the Moff or Grand Moff, though in some Sectors, it was delegated to a senior subordinate.
The High Admiral Insignia
While all Moffs and Grand Moffs had viceregal authority over the Imperial military forces within their Sectors, there is no evidence that they held any specifically military commission additional to the titles of High Admiral and/or Surface Marshal; it seems likely, therefore, that the rank insignia worn by Imperial governors were in fact indicative of these military ranks. It is not clear, however, how much "High Admiral" was a formal grade in the Navy chain of command, and how much it was in itself a form of state dignity.