Mountbatten was fourth sea lord in 1950–52, commander in chief of the Mediterranean fleet in 1952–54, and first sea lord in 1955–59. He became an admiral of the fleet in 1956 and served as chief of the United Kingdom Defense Staff and chairman of the Chiefs of Staff Committee in 1959–65.
https://www.britannica.com/biography/Louis-Mountbatten-1st-Earl-Mountbatten

