What service did the Air Force separate from?

The United States Air Force was established as a separate branch of the military on September 18, 1947, through the National Security Act of 1947. Prior to this separation, aviation forces were part of the Army, specifically under the Army Air Corps. The creation of the Air Force marked an important transition for the United States military by recognizing the unique operational requirements and strategic importance of air power, necessitating an independent service dedicated specifically to those needs. This separation allowed the Air Force to focus entirely on air warfare and aerospace operations, diverging from the broader responsibilities of the Army.

The other branches—such as the Navy, Marine Corps, and Coast Guard—were not directly involved in this transition. Each of them has its distinct roles within the military structure, but only the Army was the precursor to the formation of the Air Force. Thus, the correct answer highlights the historical context of the Air Force’s origins and its evolution into a standalone service.