With good cause, historians have long lauded General George Marshall as the central military figure in Franklin D. Roosevelt’s prosecution of World War II. As “the Organizer of Victory” Marshall swiftly morphed the tiny U.S. Army (16^th largest in the world in 1936) in the second largest and best-equipped in the world by war’s end. However, in “The Second Most Powerful Man in the World,” Phillips O’Brien, an American and professor of strategic studies at the University of St. Andrews in Scotland, makes a detailed and persuasive case, that the most important American military figure in the American war effort was not Marshall or Generals Eisenhower or MacArthur or Admirals King, Nimitz or Halsey, but the lesser-known Admiral William D. Leahy. The influence of Leahy on the conduct of the war was generally known at the time. Perhaps because he did not seek publicity, his primacy seems to have been lost to history in the face of countless worshipful biographies of Marshall, MacArthur and Eisenhower.

Leahy was first thrown together with the young Assistant Secretary of the Navy Franklin Roosevelt. Lt. Commander Leahy was acting head of Naval Personnel, a position usually held by an Admiral. The two men had a similar outlook on the Navy and life in general. They became social as well as professional friends. FDR saw to it that no Admiral was appointed to replace Acting Chief Leahy. Over the years Leahy kept in touch with FDR visiting him at his home at Hyde Park, NY. When Roosevelt became President, he appointed his old friend, by then Admiral Leahy, as Chief of Naval Operations (CNO). Although under the Navy’s old “bureau” system, the CNO was just one of several Admirals heading bureaus reporting to the Secretary of the Navy, the CNO was the one with the most contact with the President. Due to the illness of Secretary of the Navy Swanson and the political incompetence of the Assistant Secretary Edison, Leahy represented the Navy at cabinet meetings and other sensitive political functions. Leahy also resumed his status as personal and social friend to FDR.

In 1939 Leahy reached the Navy’s mandatory retirement age of 64 and was obliged to retire. On a Caribbean fishing trip FDR had casually told Leahy he wanted Leahy to accept appointment as Governor of Puerto Rico to build up naval defenses in the Caribbean in light of the prospects of war. As Governor, he also promoted New Deal policies and employed many impoverished Puerto Ricans in the construction of a major naval base at Vieques and what became known as Roosevelt Roads Naval Air Station. Roosevelt had promised Leahy that, in the event of war, he would recall Leahy to duty at the White House.

When war came to Europe, however, FDR first appointed Leahy as Ambassador to Vichy France. Leahy not only gathered familiarity with the European political scene but knowledge of French political and military personalities and, significantly, the situation in French North Africa. After Pearl Harbor Leahy was recalled to the White House.

Leahy provided shrewd and disinterested advice on war and international politics. The author notes another essential quality of Leahy’s that fueled his rise in the Navy as well as his skill influencing two very different Presidents, Roosevelt and Truman – his talent for “kissing ass.” Leahy made it a point to express disagreement occasionally with the President, occasionally persuading him, but always carrying out Presidential orders, keeping any disagreement private.

FDR’s principal civilian advisors on foreign policy and the looming war had been Sumner Welles of the State Department and White House advisor and Lend-Lease head Harry Hopkins. At first leery of Leahy’s influence, Hopkins soon partnered with him. Hopkins was sidelined by illness and Welles by personal scandal. Leahy soon eclipsed both.

By the end of the war nearly all communications to or from FDR and the service chiefs and the State Department went through Leahy.  The Chiefs’ requests were always accompanied by Leahy’s advice at his daily morning meetings with the President. FDR’s orders were transmitted to the Chiefs by Leahy, although they had no way of telling which orders were his own.

The Joint Chiefs structure created by FDR by executive order designated his own military Chief of Staff as Chairman was replaced by a statutory one after the war, including a Chairman reporting to the Secretary of Defense. Leahy himself supported this change even at the expense of his own authority as he regarded the position as too powerful to be permanent in a democracy.

During the war, the chiefs were in great disagreement about many major issues of strategy. Time and again, Leahy’s views prevailed. The grand strategy agreed to by Roosevelt and British Prime Minister Churchill, over the objections of CNO Ernest King and General MacArthur, was “Germany first.” The Allies would fight a holding action in the Pacific, while focusing their efforts on the defeat of Germany, then turn their full efforts to defeating Japan. That policy was never officially revisited. By 1943, however, Leahy had seen to it that about 50% of American military assets were in the Pacific.

General Marshall, in particular, had urged a quick buildup of forces in Europe and a cross-channel invasion of France in 1942, while the CNO, Admiral Ernest King favored more action in the Pacific. With his insights on the French and knowledge of German weakness in French North Africa, Leahy successfully argued for the 1942 invasion there. Historians generally agree that a 1942 cross-channel attack with inexperienced troops would have been a disaster.

When the 5-star ranks of General of the Armies and Fleet Admiral were created in December 1944, FDR made sure that Leahy’s promotion was effective a day before those of Marshall, King, MacArthur, Eisenhower, Nimitz, Halsey and Arnold, so that Leahy would be senior in rank. Leahy remains the senior US military officer ever, with the exception of George Washington.

Leahy’s influence continued under Truman with whom Leahy became a poker and Florida fishing buddy. His foreign policy influenced waned, however, in the face of Truman’s hero worship of General Marshall who ultimately became his Secretary of State.

Alone among top presidential military advisors, Leahy had a horror of the Atomic Bomb. He originally opposed an invasion of Japan, as he believed that U.S. naval and air superiority would doom Japan, although a blockade would take longer. He could not prevent Truman’s use of the bomb for a quicker victory while still avoiding the casualties of an invasion.

After the war Marshall, as a special envoy to China and then as Secretary of State, halted military aid to the Nationalist regime of General Chiang Kai-shek to persuade Chiang to follow U.S. policy.. Leahy unsuccessfully tried to get Truman to overrule Marshall and provide military assistance. Without that aid to the Nationalists, the Communist forces were able to overrun China and drive Chiang to Formosa.

The book is an enjoyable read and makes a persuasive case on a new historical insight into America’s conduct of the war.