Air Force Day is a celebration of airpower in the aftermath of World War Two. This observance is slightly complicated due to the nature of American air power at the time, but the designation of Air Force Day was an important step toward the recognition of United States air superiority in both Europe and Asia at the time.
Air Force Day was last observed on August 1, 1949. The Air Force Birthday is celebrated on September 18th each year.
It also likely brought the Department of Defense a step or two closer to establishing what we now know as the United States Air Force, thanks to the increased awareness of air power as an effective tool in modern warfare.