Rear Admiral Bradley A. Fiske was at the vanguard of new technology in naval guns and gunnery, thanks to his innovations in fire control 1890–1910. He immediately grasped the potential for air power, and called for the development of a torpedo plane. Fiske, as aide for operations in 1913–15 to Assistant Secretary Franklin D. Roosevelt, proposed a radical reorganization of the Navy to make it a war-fighting instrument. Fiske wanted to centralize authority in a chief of naval operations and an expert staff that would develop new strategies, oversee the construction of a larger fleet, coordinate war planning including force structure, mobilization plans, and industrial base, and ensure that the US Navy possessed the best possible war machines. Eventually, the Navy adopted his reforms and by 1915 started to reorganize for possible involvement in the World War then underway.

Answer this question, if possible (if impossible, reply "unanswerable"):  What assistant naval secretary did Fiske serve over?
unanswerable