The act created the National Military Establishment (renamed Department of Defense in 1949), which was composed of three subordinate Military Departments, namely the Department of the Army, the Department of the Navy, and the newly created Department of the Air Force. Prior to 1947, the responsibility for military aviation was shared between the Army (for land-based operations), the Navy (for sea-based operations from aircraft carriers and amphibious aircraft), and the Marine Corps (for close air support of infantry operations). The 1940s proved to be important in other ways as well. In 1947, Captain Chuck Yeager broke the sound barrier in his X-1 rocket-powered aircraft, beginning a new era of aeronautics in America.

What was the National Military Establishment renamed in 1949?