Comment by dragonwriter

> All you are describing is a restructuring of which the Department of War had gone through repeatedly throughout its history

No, from 1789 to 1947 there were two separate cabinet-level departments, War and Navy.

> It's not like it had the same structure, or anything remotely like it, in 1942 as in 1789

Internal to the two cabinet-level departments? Probably not.

At the cabinet level? There was exactly the same structure: the Department of War with the Army underneath it and the Department of the Navy with the Navy and Marine Corps.

The War Department did not become the Defense Department. In 1947 War was split into Army and Air Force, and a fourth cabinet secretary, the Secretary of Defense was added, heading the combined National Military Establishment that was created over both what had been the War Department and what still was the Navy Department (all still cabinet level departments). In 1949, the three service secretaries (two of which headed parts of what had been the War Department) were formally subordinated to the Secretary of Defense and the NME was renamed the Department of Defense. The Department of War was direct predecessor to the Departments of the Army and Air Force, not the Department of Defense, which was a new level of coordination interposed between the President and the formerly organizationally-separated services.