They needed a separate service to hide all the black projects and funding for paperclip research and development of secret space programs and off world activities.
The AF used to get half the pentagon budget on the surface and there were a thousand other diversionary programs in other departments and agencies and that wound up in black projects.
Remember the $600 hammers? Hammer $5 … black budget diversionary funding $595.
Them space ships and DUMBs ain't gonna build themselves.
They gotta have a boogie man and wars or the machine slows down. Humans are just slave labor. Always been.
The Air Force is a device, just like the rest of the charade.