High Admiral was the title borne 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.
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.
Behind the scenes
The title of High Admiral was introduced in the Imperial Sourcebook; the same publication shows a rank plaque for a Priority Sector High Commander which corresponds to the badge worn by Grand Moff Wilhuff Tarkin in A New Hope, although code cylinders are not shown in this illustration: this may indicate the insignia of the High Admiral/Surface Marshal of an Oversector.
A number of fanon sources—some perhaps unaware of the implicit connection between the roles of High Admiral and sector governor—have identified High Admiral and Moffs as distinct ranks, separate within the hierarchy, and have suggested alternative rank insignia for the position of High Admiral. Probably the most influential of these has been the Star Wars Technical Commentaries website (see here) but these fanon systems remain entirely unofficial.
- Star Wars: Empire at War (Mentioned only)
- X-Wing: The Bacta War (Mentioned only)
- Children of the Jedi (First mentioned)
- Darksaber (First appearance)
- Imperial Sourcebook (First mentioned)
- Pirates & Privateers
- Cynabar's Fantastic Technology: Droids
- The Complete Star Wars Encyclopedia
- The Essential Guide to Warfare