Master of ships
From A Wiki of Ice and Fire
The Master of Ships is the king's advisor charged with running the navy. Duties of the Master of Ships include arranging for the building and maitaince of warships and obtaining crew for the warship and commanding navel operations. The Master of Coin also sits on the small council.
History
After the death of Tywin Lannister, Queen Regent Cersei renamed the office Grand Admiral.
List of Known Masters of Ships
Stannis Baratheon Mace Tyrell Aurane Waters