What legislative act led to the establishment of the United States Air Force?

The establishment of the United States Air Force was a significant milestone in military history, directly arising from the National Defense Act of 1947. This act was pivotal as it formalized the separation of the Air Force from the Army, transforming it into an independent branch of the armed forces.

Prior to this act, air power was largely part of the Army, but post-World War II recognized the need for a distinct air service that could independently operate and strategize for modern warfare. The National Defense Act of 1947 not only established the Air Force as a separate entity but also provided a framework for the reorganization and modernization of U.S. military forces to address new global threats, emphasizing the importance of air power in achieving national defense objectives.

In contrast, while the other options mention various defense acts from around that time, they do not specifically lead to the creation of the separate Air Force. Instead, they either pertain to broader military organization changes or occurred before the Air Force was officially established. Thus, the National Defense Act of 1947 is correctly identified as the transformative legislation that fulfilled the necessity for an independent air service.