When & How Did The US Air Force Start?

The United States Air Force officially came into existence on July 26, 1947 when it was split off from the Army. Still, the Army didn’t give up on aviation, and it currently operates the world’s largest (mostly) helicopter air force in the world. Even though the US Air Force didn’t exist in WW2 (as an independent service branch), its United States Army Air Force forebears obviously did. So, just when did the Air Force start?