The Pacific Ocean posed problems for the Allies during World War II: It was too big for one commander to oversee and the different Allied services were having spitting matches — if the Navy had command of the Pacific, the Army was mad, and vice versa. The Allies, therefore, decided to split responsibility between two commanders, one Army and one Navy.

General Douglas MacArthur commanded the Allied forces within an area that included Australia, New Guinea, the Dutch East Indies, and the Philippines. He was in charge of primary ground and air forces. (The Navy had a hard time letting an army general command a fleet, but eventually it happened.)

Admiral Chester W. Nimitz, commander of the Pacific Fleet, was the Allied commander responsible for the rest of the Pacific, from the west coast of North America to the coasts of China and the Soviet Union. Nimitz had no ground forces outside of the Marines, who were part of the fleet. (Later in the war, Nimitz would have Army forces under his command as well.)