0 an officer of the highest rank in the US Navy: --
[ as form of address ] Yes, Fleet Admiral.
Fleet Admiral Nimitz/Chester Nimitz
High admirals use the same rank badge, but only wear one code cylinder while fleet admirals wear two.
As such, most fleet admirals answer to a high admiral who in turn answers to a moff, grand moff, or supreme moff.
Retired marshals, chief marshals, army generals, and fleet admirals, however, were allowed to retain their former ranks and their corresponding stars.
This rank is similar to fleet admiral.
Usually it is the most senior peacetime rank, with more senior ranks (for example, field marshal, air chief marshal, fleet admiral) being used only in wartime, or as honorary titles.
The rank usually refers to the position of full admiral (equivalent to full general) and above vice admiral and below admiral of the fleet (or fleet admiral).
At one point the captain made preparations to abandon ship, but was then overruled by the fleet admiral who believed the ship could be saved.
It ranks above vice admiral ("three-star admiral") and below fleet admiral ("five-star admiral").