From the author of the acclaimed biography of Harry Hopkins comes this first full-scale portrait of Franklin D. Roosevelt's top military advisor, Fleet Admiral William D. Leahy. The president's personal chief of staff and chairman of the newly established Joint Chiefs of Staff, Admiral Leahy was the highest-ranking military officer in the nation and one of the most powerful men in Washington during the war years. Along with Hopkins he enjoyed Roosevelt's complete trust. But unlike his better-known White House counterpart and the prominent military leaders of the day, Leahy quietly performed his valuable services behind the scenes. Consequently, he never received the fame of his more dynamic colleagues and soon after retirement faded into history.   Henry H. Adams takes this forgotten figure out of the shadows and places him beside the president he so brilliantly and devotedly served. He shows how Leahy, as FDR's confidant, his contributions to the war effort were so valuable that Adams credits Leahy, along with Hopkins, as being chiefly responsible for the smooth transfer of power to Truman upon Roosevelt's death.   This biography is equally revealing of Leahy's earlier years of service to the government as chief of naval starting the buildup of what would become a powerful two-ocean navy. It describes his brief but important tenure as governor of Puerto Rico and his later service as ambassador to Vichy France.   Witness to Power ensures that Leahy, because of the central role he played during one of America's most important eras, will assume his rightful place on the historical stage.