Fleet Admiral William Daniel Leahy (May 6, 1875 – July 20, 1959) was an American naval officer who served as the senior-most United States military officer on active duty during the Second World War. As Chief of Naval Operations from 1937 to 1939, he was the senior officer in Navy, overseeing the preparations for war. After retiring from the Navy, he was appointed in 1939 by his close friend President Franklin D. Roosevelt as Governor of Puerto Rico. In his most controversial role, he was appointed as Ambassador to Vichy France, which was an ally of Nazi Germany, 1940-42.