What did the National Security Act of 1947 establish on September 18, 1947?

The National Security Act of 1947 was a significant legislative milestone in the history of the United States military. One of its primary achievements was the establishment of the Air Force as an independent branch of the armed services. Prior to this act, the Air Force was part of the Army and referred to as the Army Air Forces. The law recognized the importance of air power and the necessity for a dedicated branch to focus solely on aerial warfare and operations.

This separation allowed the newly created Air Force to develop its own identity, leadership structure, and strategic vision, which was crucial during a time when air power was increasingly seen as vital to national defense. The act also set the stage for a more unified command structure and better coordination among the different military services through agencies like the National Security Council.

The other options, while they pertain to military reorganization, do not accurately reflect the primary outcome of the National Security Act of 1947. The Army and Navy were well-established prior to this act, and the legislation did not involve the creation or formation of these branches in the sense suggested by the other choices.