What legislation established a separate and independent Department of the Air Force?

The National Security Act of 1947 is the legislation that established the United States Air Force as a separate and independent branch of the armed forces. This act reorganized the military and created the National Military Establishment, which included the Department of the Air Force, along with the Department of the Army and the Department of the Navy. It marked a significant change in the U.S. military structure by emphasizing the importance of air power as a distinct component of national defense and allowed for more streamlined command and control over air forces. This foundational change laid the groundwork for the evolution of the U.S. Air Force and its role in modern military operations. Other options do not hold the same historical significance in the context of establishing the Air Force as a separate entity.