…except the Navy and Marine Corps, which was the original point. A large part of the Second World War was fought by the naval services, despite those services being outside the Department of War. During the war, overall coordination of the military was not carried out by the War Department but rather via the Joint Chiefs of Staff and through ad hoc high level coordination between Army and Naval command. In particular, command in the Pacific theater was split between General Douglas MacArthur Admiral Chester Nimitz (with the ground operations under Nimitz being primarily carried out by Marines). The difficulties caused by this approach were the primary motivation for the reorganization of the American military into a unified Department of Defense.

I am well aware that the Army Air Forces were a very large part of the Army during the Second World War. However, the Navy and Marines also had tens of thousands of airplanes, none of which were under the control of the War Department or the Army Air Forces. It’s a little misleading to claim the War Department controlled the “entire air force” when they only controlled the Army Air Forces and not naval aviation.

The War Department controlled the Army and the Army Air Forces, which were part of the Army at the time, so it’s just as correct and a lot quicker to say that the War Department was only in charge of the Army. It wasn’t in charge of the Navy and Marines, and it wasn’t even in charge of fighting wars because we needed the Navy and Marines to help fight wars and they were under a different department. Which, again, was the reason for forming the Department of Defense in the first place.

When the Air Force became an independent service during the postwar military reorganizations, they actually tried (and failed) to take over naval aviation; to this day the United States Navy has a larger air force than most countries.