Which branch of the military was the Air Force originally a part of?

The Air Force was originally part of the United States Army. This relationship dates back to the early 20th century when aviation was developing as a military capability. The Army established the Aeronautical Division in 1907, followed by the creation of the Army Air Service during World War I. It wasn't until September 18, 1947, that the Air Force became an independent branch of the military through the National Security Act of 1947, officially separating it from the Army. This historical context underscores the long-standing connection between the Air Force and the Army prior to its establishment as an independent service. Understanding this lineage is crucial for grasping how current military structure and operations have evolved from their origins.