Admiral of the Fleet James Gambier, 1st Baron Gambier, was a Royal Navy officer. After seeing action at the capture of Charleston during the American Revolutionary War, he saw action again, as captain of the third-rate HMS Defence, at the battle of the Glorious First of June in 1794, during the French Revolutionary Wars, gaining the distinction of commanding the first ship to break through the enemy line.

Admiral of the Fleet is a five-star naval officer rank and the highest rank of the Royal Navy, formally established in 1688. The five-star NATO rank code is OF-10, equivalent to a field marshal in the British Army or a Marshal of the Royal Air Force. Apart from honorary appointments, no new admirals of the fleet have been named since 1995, and no honorary appointments have been made since 2014.