“In connection with the matter of command in the field, there is perhaps a popular misconception that the Army and the Navy were intermingled in a standard form of joint operational organization in every theater throughout the world. Actually, the situation was never the same in any two areas. For example, after General of the Army Dwight D. Eisenhower had completed his landing in Normandy, his operation became purely a land campaign. The Navy was responsible for maintaining the line of communications across the ocean and for certain supply operations in the ports of Europe, and small naval groups became part of the land army for certain special purposes, such as the boat groups which helped in the crossing of the Rhine. But the strategy and tactics of the great battles leading up to the surrender of Germany were primarily army affairs and no naval officer had anything directly to do with the command of this land campaign. A different situation existed in the Pacific, where, in the process of capturing small atolls, the fighting was almost entirely within range of naval gunfire; that is to say, the whole operation of capturing an atoll was amphibious in nature, with artillery and air-support primarily naval. This situation called for a mixed Army-Navy organization which was entrusted to the command of Fleet Admiral Nimitz. A still different situation existed in the early days of the war during the Solomon Islands campaign where Army and Navy became, of necessity, so thoroughly intermingled that they were, to all practical purposes, a single service directed by Admiral William F. Halsey, Jr. Under General of the Army Douglas MacArthur, Army, Army Aviation, and the naval components of his command were separate entities tied together only at the top in the person of General MacArthur himself. In the Mediterranean the scheme of command differed somewhat from all the others.”

Third Report, p. 172
U.S. Navy at War, 1941-1945: Official Reports to the Secretary of the Navy (1946)