From 1954 to 1959, Mountbatten was First Sea Lord, a position that had been held by his father, Prince Louis of Battenberg, some forty years earlier. Thereafter he served as Chief of the Defence Staff until 1965, making him the longest-serving professional head of the British Armed Forces to date.
https://en.wikipedia.org/wiki/Louis_Mountbatten,_1st_Earl_Mountbatten_of_Burma