Rear Admiral
From One Piece Encyclopedia
"Rear admiral" is a naval commissioned officer rank that is usually two-star rank ranking below Vice Admiral.
Each Naval Squadron would be assigned an admiral as its head, who would command from the centre vessel and direct the activities of the squadron. The admiral would in turn be assisted by a vice, or vice admiral, who commanded the lead ships which would bear the brunt of a naval assault.
In the rear of the Naval Squadron, a third admiral would command the remaining ships and, as this section of the squadron was considered the least dangerous, the admiral in command of the rear would typically be the most junior of the squadron admirals. This has survived into the modern age, with the rank of rear admiral the first and junior-most of the admiralty ranks of most navies.
So far the only person seen in One Piece to have held the rank of Rear Admiral is former marine and current pirate X. Drake and an unknown Rear Admiral who was in command of the battleships of Impel Down when they were after the Jailbreak League's battleship. The highest seen currently used rank seen, below Vice-Admiral, is currently that of Commodore.
